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AN ELEMENTARY ASTRONOMY FIRST EDITION by H. MATTISON Classic Literature Collection World Public Library.org Title: AN ELEMENTARY ASTRONOMY, FIRST EDITION Author: H. MATTISON Language: English Subject: Fiction, Literature 'LJLWDOPublisher: World Public Library Association Copyright © 20, All Rights Reserved Worldwide by World Public Library, www.WorldLibrary.net World Public Library The World Public Library, www.WorldLibrary.net is an effort to preserve and disseminate classic works of literature, serials, bibliographies, dictionaries, encyclopedias, and other reference works in a number of languages and countries around the world. Our mission is to serve the public, aid students and educators by providing public access to the world's most complete collection of electronic books on-line as well as offer a variety of services and resources that support and strengthen the instructional programs of education, elementary through post baccalaureate studies. This file was produced as part of the "eBook Campaign" to promote literacy, accessibility, and enhanced reading. Authors, publishers, librariDQV and technologists uniteG to expand reading with eBooks. Support online literacy by becoming a member of the World Public Library, http://www.WorldLibrary.net/Join.htm. Copyright © 20, All Rights Reserved Worldwide by World Public Library, www.WorldLibrary.net www.worldlibrary.net *This eBook has certain copyright implications you should read.* This book is copyrighted by the World Public Library. With permission copies may be distributed so long as such copies (1) are for your or others personal use only, and (2) are not distributed or used commercially. Prohibited distribution includes any service that offers this file for download or commercial distribution in any form, (See complete disclaimer http://WorldLibrary.net/Copyrights.html). World Public Library Association P.O. Box 22687 Honolulu, Hawaii 96823 [email protected] Copyright © 20, All Rights Reserved Worldwide by World Public Library, www.WorldLibrary.net i .. AN • :/~ r ~. ~. ELEMENTARY ASTRONOMY, • . I'OK ACADEMIES AND SCHO.OLS • • ILLUBTllATED BY NUllEB.OUB OlllGINAL DIAGRAMS, AND ADArI'EC ro USE EITHER WITH Oil WITHOUT THE AUTHOR'S LARGE MAPS. BY H. MATTISON. ~ i I'IPTB BDITIO.-TWBLI'TK ...OUI.A..D. , - NEW YORK: PUBLISHED BY HUNTINOTON AND SAV AGB, 216 PEARL STREET. CINCINNA.TI :-H. W. DBRBY 1849. &, CO PREF ACE. , . Tu P~Dt ie, emphatically, an ap of _tili". Bowe.er profollDd and accurate a book. may be, its career will be brief and ita circulation limited, unle. it .. eminently prGctieGI, and wi_lyadapted to its purpose. Heoce it often happeD8, that pel'8OD. of andoubted abiliti. as men of learning, have utterly failed in their attemPts to produce avail .. able ten ..boob in their feapective departmentl of lItudy. Exper~ence • .. a teacher, and tac~ as a compiler, are .. important to the author of a IChool-book, 88 a koowledge of the subject upon which he writes. And even with aU ,theae endowments, few writers • • of elementary worb are satisfied with their own production. till actual use in the school..room hu shOWD whereio they are defective, or waDtitJg in adaptation, and of what improvemenu they are capable. Hence almost every new school-book is "reviled and improved," before it passes to a second edition. The ELEIIBHT...Y AII'BONOXY and AaTaoNOliloAL MAN han now been before the public about eighteen mont,ba, during which time about 0fI6 tloU8tJftd .et. of mil", and tt'll tAouGnd oopl. of the book have been BOld. These have gone into Ule in ..Imost every state of the U mon, and every grade of sChools, from the -Common School to thea University. One set of maps, and a supply 'Of book., were ordefed by a Scotch lady, who had WJed the work iD her own eeminary in thla country, to be used in a mOdel school in EdiBburgh, ScotJaDd. During the put year both the author and publilhe.. have taken .pecial pain. to aaeertain the views of "."ctieG~ t,GcA.,._, w~..ere tJCtfMJlly wing the worltt aDd to obt~n any auggeitioDB which might be of .nice in renderiDg fRture edido_ more perfect and complete ; and the unanimity and cordiality with, which all wch have commended the WQIK, ia truly gratifying and encouraging. A few alterati0D8 and improvements have beeD IUI'~, 80me of which we have endeavored to profit. SooB after the Second Edition was publilbed, we weM requested by teacben in Philadelphia and eiliewben, to ~paip a IIIlit of appropriate Qu._tiou on Uhe LeMa. A.ccordiDglyJ t.heee appeal in the b, ( PUI-A.OJl. Third Edition, in the form of an Appendix, and are lItiU continoed They can, therefore, be uaed or not, at tbe di8cretion of the teacher. . To adapt the work to private leamen, and to school. that c&llDOt parchue the large maps, it is DOW _eel with the large maps in miniature, intel'8pemed among the le8IOIUL Theee beiDg exact copies of the Originals, though upon a .maller leale, we have not only a magnidcent let of charts for lectu1'e8 and illWltratioos in the school-room, bot each learner has a set of tA, . . . flllJfM in hie text-book, and can, ther. fore, pursue biB .tueliea either with or without the large maps, acCOl'Ging to circumstance& Tb"e text, however, bu not been altered; .. that the book is still perfectly adapted to the large mapa, and CaD be uaed with former editiooa, as if it had not been illWltrated. 10 a few instances the language of the book nec8l8arily sup.,.. the large maps to be in view, all OD pages 32 and 201; but these 08881 are rare. AJJ the large and lIIDall maps are the llaJDe, if the test • adapted toJo one, it ml18t be to both. The diagrams are in.ned where they are first referred to, and are made to face the right, 80 U to be e..ily kept in view while Itudymc the leIBoD8 that follow. It is confidently belieYed that the peculiariti. of thi. work are I1lOh as will oommend it to geDeral favor, and laoure for it mcreuing popularity, and an en viable and luting reputatioD. 1. In the first place, the fMtAod or plcn of the work is eminently original. "One thieg at a time," and" eyery thing in its place," baft been the author's mottoee. It begins at hom«>, or with the Solar Sya&em, and ends in the more distant or Sidereal Heavens. The Earth is treated of astronomically, or as a/ planet; and iD8tead of digre.in, wben we come to her, to coDiider her MOOD, aDd the phenomena of Eclip881 and Tidea, theee subjects, and all othen pertaining to the lteCoDdary planets, are reeerveel for their appropriate place&. Tide. and Eelipee8 ue by no means peculiar to our clobe ; why, then, should we aacrifice a philoeophical cl...moatioD, and foist in the MOOD, with the lubjects of Tid. and Eolipeee, before we have done with the pri-- .. marl.? Another prominent feature in the arranpmeDt, anel one tbai will please every practical Le~oher, is, that tbe !GCu of tl~ .eN,are cl.8,ified. Instead of naming a planet at the bead of a leMOD or chapter, and then giving its diltaoce, magnitRde, deDBity, veloeily, periQd, &c., all miDIleel together upon the llCUDe page, violatiDa &be lairs of ~ia1ioD. aDd .tting at defiaDce the eftOrta ~ mem- I .. PBZI'ACJI. ory, all fact. 01 the _me kiDd are here cl&lled together; • 6 that the whole lICience is reduced to' 8)'8tem aDd order. For iDBtaDce, wb_ the Primary Planet. are taken ap, the fiI'8t le.on following is deyoteci to their fttlfR4!. and _'roftf1fRic.1 ~. Il80000 to their tl~. ttJace., &0., 10 that their temperature, mapituct., deaaiti_, perioda, 8e880D8, &e., constitute 10 many dilttiDct le.o... ; cODIeClReDtly, th. facts can not only be read, but let.mletl and r",...6.,fL 2. A secoDd characteristic of the work is, that it .. more lully mu.ttated than lUly other work, of the IllUDe fonn, thai bu ev~r beeD publiBbed in tb. country. ADd yet it iI Dot a mere picture-book, in wbich a noble lCience hu been trifled with, aDd 8&Cli6ced to a deeire to catch the eye, aDd eell the book. The ide. 01 devoug fJ'fery other page of a scientific work excluaively to iIlO8tratio., and at the I8IDe time doiDIJ any kind" of justice to the .object on the iDtermediate pagel, is altogether chimerical. It would be too mucb like a farm, one.half of which W&8 devoted to a 8ower.prden; or like IIOID8 of our ill... trated holiday-papel8. 3. The leading desiga beiDr to furailb aD avaiJabie text.book ". Aatronomy for Common Schools and Academiea, 18 well 88 for pri"Yate students, tbe author baa confined hi~lf mainly to what may be caUed the fact. of the aaience, or in other words, to the r,,,,lt. wbi~b have been arrived at by the labore of the ob8ervatory IUld tbe 1'8aearchea of the mathematician. The atructare aDd Wte of inl&rumeDte, and the calcu~tjona and p~ by which the faots of the ecieoce are arrived at, are deeignedly omiUecl. ' Theee may be neC8ll&l")' in text-boob for our higber, iD.titutiou of learning, but they caD neyer become legitimate lubjects of primary iustruction For similar reaIOn., the mythological history of the lOieDce hal been dilcarded. 4. We have adapted the work to the present ltate of the ecieuce by embodying the etatistice of eeveral ..., plGuu, recently ciUIcoveJ'tid, the recent observatioD' of Lord Ro.t upon the MOOD and the diatlWt N ebul." and the IUbliGle and almost overwhelmm, anDOUDcement of Midler in iegard to ille " Central Sun." 5. When used in connection with the large maps, the work combiDes all the advantagee of blaokboard iUustratioDl, with tbe mOBt pa.. tieDt study of a text ..book. . All the diagrams in the book are found in the corresponding maps, upon a very large .cale, 80 that every explanatiou from the mapa, by the teacher, aerves t.o render the diagrams in tbe book more interestiDI and intelligible. Another strikillg ad- l'utage of this method of teaching Aatronomy la, that whatever ilh.· .,..z.; 8· PBBJ-AOB. tratiOIUJ are given by the toaeber, beneftt the whole ell. alib, • without the labor repetition to each echolar, over a diagram iD the book. Thia ..viDI of time aDd repeated explanations to difFereot pupils, wiD be read,ily appreciated by every practical jnatructor~ Again, many of theee draWiDP are ""irel, origiul, and in the opiaion of competeDt jl1da-, better calculated to conyey a correct and permanent idea to the miDd, than aDY that baye heretofore appeared. 6. Though adapted to QII8 with the .riea of large maps, it is, at the laDle time, complete in iteelf, and can be used 88 well independently of them 88 if it had DO connection with them whatever. Thi8 i. an important advantage. 7. To all tbeee we mJly add that, all thinp considered, it ill ~ "lNape.' text·book of Astronomy that has ever been publi8hed ill America. A cl. . of thirty 8Chol&rl can be supplied at retail with a . . of the large map', and a book for each for 130. A school of 100 can procure a Bet of map' and a book for each pupil for 165. ' If procured at wholesale prices, a eet of mapa Cor the 8Chool-room, aDd • hook for each pupil, would cost Ita than ftfty ceil" per echolar; and the IDOre scholaJ'l, the Ita the expen8e to each. Where, then, we uk, can tbe same facilitiea for aoquiring a knowledge of Astronomy be procured for the ..me money 1 We commeDd this cOnAideration eepecially to thOle having charge of large echool8 in our citiee and allewhere. Such are aome of the peculiaritiea of the ELBlllurr.IlY ABTaONOIIY; aDd upon theee we can lafely I'fJIIt oar claiml to public patronage, in lending it forth to the world. ID ita preparation for the Prell, the aGthor has availed himaelf of all the hel.. within his reach. He h. OOD8Ulted all the boob UPOD the wbject that were available in th. COIIDtry t U well .. many practical teacheJ'll, and gentlemen of acknowledged ecientific abilitieL But while on the one hand he has used boob as writen generally uae them, namely, &8 IOUlCe8 of knowledge, aDd haa advised with meD of learniDg and experience i~ regald to many particulars, the author feels bound, in jU8tice to himaelf, to claim for hie work a good degree of originality; and to .y, that whether good or bad, it is, iD the main, his own, and not the work of another. It ill only D8CeII&I'J to add, that the ltatiatica in the ttlble& are generally giveo in round DumbelB, and aceonliDg to what. were considered the highest authoritiee. or !law Yoalt, Ja. I, IMg. "1 - . TO TEAOHERS. - Tn"R are .veral way. in which thiI work may be used to .d- yutage. 1. It may be Itudied prec_ly like aoy other text-book, and the pupil examined by the printed, or by extemporaDeoUIJ question&. Thill ia the usual method in tbose lCbools whicb have not the large maps. and in academies and eeminaries where the pupil. Itudy in tbeir rooms, and aee the large mapa ooly in the recitation-room. 2. Wherever the large maps can be obtained, and the pupils aU lItudy iu tho lame room, and only during ecbool bours, Astronomy lhouJd be made a K,ner.l I~trciH two or three timea every week. The mapa to which the leaaoDI refer, should be 8uspended on the BOuth side of the room, if practicable, (to answer to the natuml position 01 many of the obje~" in the heavens,) and the lelllOD studied with cooittant reference to the maps. Tbey are 10 much more attractive and imposing, and tbe figures 80 mtlch more distinct and prominent thaD the cuts in the book, 88 to give them a decided advantage over all ordinary illustrations. They should, tberefore, be procured wherever practicable, and used in connection with this work. 3. A third method of ueinr the work, is to 1IIe it a•• rIdding-boot two or three dmee a week, either with or without the Jarge eharts. II these are ill the school, theyebould be It18peDd~d before the cia. during the exercise. By tbil method the pupil wil1leam to pronounee acientific terDll correctly, to read figuJ:ee with facility, to read with atteDtion, and to remember what he read-. Beeidee, DO extra tjme will be required. The pupil is leaming to read, and at the same time studying a science. By tbe 1188 of the mapa the teacher can illustrate the leMolKI as he goel along, and a wholesome interest wUl be 8U8tained throughout. The questioos in the Appendix will be found convenient in reYiewing tbe J88IOD& Teachers will find tbis aD efficient and delightful method of teaching Astronomy. 4. Several of the tables in the first part of the work should be committeod to memory; lucb as the names, dialances, magnitudes, &c., of tbe primary planetS. If Uie teacher prefer, they may be learned by concel1 recitatloo&' .... 8 TO TEACHBRS. 5. Tbe UUonomicalligoa in Leaaon 7th should be draWD upon the blackboard by th'e leamer, and explained. It would aJ~ be useful for him OCCasioDalIy to draw map' of di1FereDt celestial qbjects, from memory. &. In lOIDe CUEI8, the whole IQbject may be preeented orally by the teacher, in • aeries of evening lectoree, following the C01l1'8e 9f the book; but this .bowd rather be in tJddititm to the replar .ady dorin. IChool hoUl'l, than a mbetitute for it. 7. After aU, much win depeod upon the judgment and ingeouity of the teacher, aod the intereet he takes in the subject. Bound leaminr caD never be acquired, by any mode of teaching, without thought and attention. N eitber can any particular oouree be struck out that wiD be adapted to all kincts of echooll, and to every part of the country. 8. To lucb teachel'l 88 have never studied tbis acien08, (and there are .,me of this 01. .,) we would say that the work iI lpecially adapted to your circulD8taooee. It is strictly elementary, DO extraneoll8 and abstrule matters darkeD ita pages, and it is not 10 voluminous .. to require a year to through it. Y oq will fiDd DO dimculty whatever iJl teachiol the lCienoe witb thil work, even though you have Dot previou~ly taught it; and a cia. iD thil deligHtful IUld sublime lCience will be the surest means of adding to your pl'ellent intellectual &torel, a knowledge of this ,important branch of study. If auy new motive be neceasary, let it be remembered that no Dew audy is 10 rapidly goill, into the primary echooJa of the country, 88 that of De-· ecriptive A.8tronomy; and the time ,is .DOt far diataDt when it will be required to be taught in every achool-house in the land. Be encouraged, then, to enter upon this Itudy. Organize your clUB at ODce, and launch oot tI01D for a knowledge 01 those fl• • of 'worlda that ail the upper deep. U entered upon in the Ipirit of a teGel", your PlOIreal will be rapid, your voyage delightful, IIl1d IUOCe18 certain. With these luggeitioDB. the work is now comlJlitteci to your hlUld& Baving been formerly identified with you 88 a practical teacher, the .athor expects the co-operation of hiB profeaaiooal friends, in leDderiD, the work usefol to the riaing generatioB, and in promot.iDc the interests of that Doble lCien08 to which it is devoted. ro I[7For a de8erlptloll of the Large Kapil, pr1cea. ealar at the end of tile Book. .~, 11M CIr- CONTENTS. INTRODUCTION. ~ I. . I. I. 'I 0.. •..•...•..••.• •••••••• ... ABtrooomy-ite Nature .. a ~ieDC8" •• Ancient li~ of Aetrouomy-the Ptolemaio 111..,........... DirHcult ies of Uie Ptolemaic Theory. •••••••••••••••••••••••••••• The (;ol1em icao S)'IItem..,. . • . . . . • . . . • . • • • . • •• • • • • •• • • • • • • • • • • • • • • FirBt Gnaad Div.oDS 01 the U DiveI'll8,. • • •• • • • •• • •• •• • • •• • • •• • • • • 11 11 I' II 11 PART I. OP THE SOLAR SYSTBM. CHAPTER I. CLAMlPJa.TION 0,. THB lOLl. mDta .. '!be Sun. Plue&a. PriIoariee. SecondariM, &0., ••••••••••••••••• II CHAPTER II. ow THK PIlIMAa, I'LlJIr8"N. ,. Names and 8.1«" of the Primary Planeta, .•••••••••••••••••••••• 8. Distances of the Planets from the 8UII, •••••••••••••••••••••••••• 10 DeKfet-lil. MinutN, and ~ecolld. explained, •••••••••••••••••••••• 10. A nt{U11&l' Distances, Ma«Ditudta.8, &c., •..•••••••••••••••••••••••• 11. The ~UII . . Been from the different Plaoeta. ••••••••••••• Ii. PhilO8Oph.J of the Diffusion of Li"ht, .••••••••••••••••••••••••••• 13. I~il(h t and Heat of the leveral Planets, ••••••••••••.•••.• 14. M ~n i I ude of the Planeta, •••••.•...••••.•••••••••••••••••••••••• 15. Relative M~Ditude of the Sun and Planets, •••••••••••.•••••••• Je. Comparative DeD8ity of Ule Plauete, ••••••••••••••• : ••••• 17. A ltrllctioll of the Plaoe~"" ••••..•••••.••.••••••••••••••••••••• 18. Periodic RevolutioDll of me Planets, ............................. . I Hourly Motion of the Planets in their Orbita, .••••••••••••••••••• 10. L"".entripelaland Centriful{al Forces, .•••••••••.•••••••••••••••••• 'II. Diurnal RevolutiODl of the PJaoets, .•••.•••••••••••••••••••••••• ti. 'rru~ FiJ{ure or tile Planeta, .••••.•••••••••••••••••••.••••••••••. o ••••••• 0 •••••••• 0 •••••• ~. The I!:cliptiC!t o. II • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • , •••• t4 Th(ll Poles the Ecliptic, •••••.••••••••••••• 15. Oblic\uity of the ~liptic, ••••..•...•••••.•••••••••••••••••.•••••• 18 1~he Zodiac ••••••••••••••••••••••••••••••••••••••••••••••••••••• n. 1'i~nl 0 ••••••••••••••••••• of ttle Zodiac••.••.•••.•••..••••••••••••••••••••.••••••••• 18. Not.lee-- Ascendin, a..cl l)eacendiu". 0 ••••••••••••••••••••••••••• II. Tra,nBiw......................................................... . •• • . IT 18 30 31 • 31 D JI •• 37 31 31 •41 48 41 •a 30. Trull.ita of Mercury, •••.••••••••••••••••.•••••••••••••••••.••••• 44 11. Transits of VflnU8~ •••••••••••••••••••••••••••••••••••••••.•.••• a a. Incl i nation of the urbita of the Planeta to th" Plue of the Ecliptic, 41 13. Ct-1t>8f illl Latitudea .•.• 34. C..elf'8lial IAlll{itud(II, • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4'7 .- 0 ••••••••••••••••••••••••••••••• : •••• 0 •••• 35. l..onl(itude of the AacencljnJ( Nod. of the Planetll, .•••••••••.•••• ... 38. C.onBtella t ione of the Zodiac, ............•.•••••••.•••••••••.•••• 10 01 17. The ~uuttl Apptlrcnt Motion in tbe Ecliptic, ••.•• ·••••••• 0 •••••••• .. 10 CONTBNTS. t-oa . ..... 38. SucceMive Appearance of the C9ostellatioDi in the Nocturnal fleav8D1, •••••.•••••••••••••.•••••••••••••••••••••••••••••••• II •• VisaKreement between the Months and SigDB,. • •• • • •• • • • • • • • • • • 40. The ~uiDoxest.. . • • • . . . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 41. Prece8Bion of the !:quinoxee...... • • • . •• • • • • • • • • • • • • • • •• • • • • • • • • a. The ~l8tiCM,.. • • • • • • • • • • • • • • • • • •• . •• • • • • • • • • • • • • • • • • • • • • • • •• • • 43. Tile ColurtllJ ••• • •• • • • • • • • • • • • •• ••• • ••• • •• ••• • ••••• ••••••• .• •••• ". Ellip.tic~ty 01 the P1~ets' Orbita........ •••••• •••••••••••• •••••• 45. P~rlhellon and Aphelion, ...••.•.••.•••.••••••••••••••' • • • • • • • • • • 46. Eccentricity of the Planets' Orbitl........ ..•. •••••••••••••••••• 41. Phil.-ophy of the Sea.aona, •••••••••••••••••••••••••••••••••••• ~ 48. The tsun'a I>eclination, • • • • •• • • •• •• • • • • • • ••• • •• •• ••••• • •• •• •••• 49. Right Aacension, •••••.••.. '. . • • • . • • •• • . • • • • •• •• • • •••• •• ••• • •••• 10. Inclination of the Axes of the Planet. to the Plane of their . . 8Jlective ()rbits.1: ........•..•••••••••.•••••••••••••••••••••••• It. Seasons of the dinerent Planets,.,. ••.•.••••••••••••••••••••••••• B. ~n. of Veo1J8,•.••••••••••••.••••••••••••••••••••••••••••••• 1.1. SeIlMlD8 o( Mam, ...••••..•••.•••.•••••••••••••••••••••••••••••• 14. Se..,ns of Jupiter, •.•.••..•.•••.•••••••••••••••••••••.••••••••• u. Se88C)D8 of Saturn, .. 16. CopjunctioD8 and OPP!l8ition of Planets. ..•••••••••••••••••••••• II • 11. IS. H. 10. II. .. 83. • • ... • • • • • • • • • • • • • • • • • • •• • • • • • •••••••••••• Sidereal and Synodic Revolutions, •••••.••••••••••••••••••••••• Elonl{8.tioD8 of a Planet, .........•..••••••••.••.••••••••••••••• When PlanetB are said to be Stationary, •••••••••••••••••• " •••• Direct and Retrograde MolioIlS, ..••••.••.•••••••••••••••••••••• Relrolrade MotioDa of the Exterior Planets••.••.••••••••••••••• Venos as Morning and Evening Star, •••••••.•••.•••••••••••••• Phases of Mercury and Venu8, ..•••••••••.••••••••••••••••••••• .Teleaoopic Views of the Planets, .••••.•••••••.••••••••••••••••• Telescopic Views of Satun), .......••...•••••.••••••••••••••••• 51 M 14 10 17 18 51 :II 60 81 • . II 15 15 trr 87 61 10 'i'I 7t 73 14 71 71 M. 11 85. 81 II. DimeD8Jons, ~tructure. and U&e8 of Saturn'. RiD.., •••••••••••• 81. or the Di8cOvery of the several Planet&, •••••••••••••••••••••••• CHAPTER III. 01' TIm "OOND~ILY •• I'LlJIr8"N. •• Character aDd Number of the Secondary Planeta,.......... •••• •• Supooeed Satellite of VeDl1!l' • • • • . •• •• . • • • • • • • • • • • • • • • • • • • • • • • • .10. Of the Earth's SateUite or moon,.......... .••••• •••••• ••••••••• '1. Chan~ or Phaaes of the MOOD, •••••••••••• • • • • • • • • • • • • • • • • • • • ft. The Moon'. Path around the Sun, .•••..• .••.• . •••••••••• ...... '71. Revolution of the MOOD'8 Nodes around the Ecliptic,. • • • • • • • • • • ,... Sidereal and Synodic Revolution of the Moon, ••••••••••••••••• ~ 11. Revolution of the Moon upon her Axi.,...... . . . . . .. ... . .. . . . . •. .,.. The Moon'. Librations.. . . . • • . . . . . . . . • • . • • . • • • • • • • • .• ••• . •• • • • • 'IT. 8eamDi {)( the Moon, . • • . . . .. . • • • • • • . • . . • • • • • • • • • • • • • • •• • • • • • • •. • 14 14 98 ., 98 98 89 II 100 100 18. TeleecoVio Viewa of the Moon,. . •• •. • . . •. . • • •• • • • . • • •• • .• . . . • •• ft. Phyaical Constitution ot the Moon-Mountains, Volcanoes. At,. mc.pheJ'e, &c.,.. . . . . . . . . . . . . . .............•......•...... ~ . .• J01 •• ~hJ of the Moon, or Selenography, •••••••••••••••••••••• 103 81. MOODS or Satellites of Jupi~,........ . .......••• ....••. ..•....• 104 B. Satellitel of &tum,.. . . • . • . • • • • • • • • • • • • • • • • •• • • • •• •• • • • • • •• •• •• 105 83. Satellites of Hel8Chel ............. ~ .•••••••••••••.••••••••••••• -101 M. Suppoaed Satellite of Le Verrier'. rlaoet., •.•••••••••••••••••••••. lOT CHAPTER IV. f'IIILOIOPBY or o. SOLJIIIIBI. D. Nature and Call1e8 F.cli............. • ••••••••••••••••••••• a 101 M. Character Extent, and Duration of Solar Eclipaee, •••••.••••••• 110 11. EcliIJeel 0 1the Mooo, .••••••••••••••••••••••••••••••••••••••••• 114 j : CONTBNTS. LI...or . the Time aod F!equency tI Eel....... . . . . . . .. . . . . •. • . . • . . .. , at. &.Ii.... or ()ccaltalioDi of the S&aiW, ••••• • •• • •• • •• • • • • •• • • •• •• 10. F.clipaee of Jupiter'. Moona........ . .......... ....•... •....•.••• II. &li.- of Salorn and Herlchel, ••••••.•••••••••••••••••••••••• 88. 11 .... J11 111 118 111 CHA.PTER V. PJIILOIOPBY ow ".. TID. . B. Nature and Call1f!J8 of Tides, •• 13. ~«iD« of the Tide-ExcW'lione in Latitude.............. • . • •• SM. ~~g and Neap Tidee-Prof. Daviee' Th.eoI'J, •••..••••••..•••• 15. Other ine.qualitiea or the Tid4t"J .••.••••.• • • • • • • • . . •• • • • • • • • • • •• II. Kobon of the Apeidee of the moon'. Orbit, •• • • • • • • • • • • • . • • . . • •• II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I_ 1. 1. 111 lIT CHAPTER VI. ow COIIBTL' 1'1. 18. II. 100. General Delcriptfon of Cometary BodiM•••••••••••••••••••• : • •• Mapitudel, Veloci~ and Temperature of Cameta,. •• ••• • •••• Penods, Distances, N umber of Comets, • • • • • • •• • • • • • • • • • • •• Direction, Orbits, Bncl Nature of Cometa.. • • • • • • • . • • . . •• • • • • • • •• 1_ 1. 1M 1_ CHAPTER VII. ow m8 IUN. 101. General Remarks ~ing the Sua-ita Magnitude, &c., .•••• 138 101. Spots on the Sun-their Number, ...••••••••••.•.•••••.•....••• 1. 103. Nature of the Solar S~,.. .... ..... . ............. . ........ .... 140 104. M agnjtude of the Solar Spots,. . • • . . • • . • •• • • • . • • • • • • • • • • • . • • . . •• 105. Revolution of the Sun uwn hIS Axis,... . . • . • . •• .• • • •• •• • . •• • • •• 101•.. ~tioDJ...Mot!0Dl!. and Phases of the Sol ... Spoil••••••••••..••• .. 187. 'PbJBICallA)D8titutIOD of the Sun,.............. • •••• ••••••.• •••• 1118. The Zc:K:liacal Lilht,..... .. .• ..•• .•• . ..... • •.••. • •••••• •••• .••• 101. MotiOD of tile Sun in SJ-ce,.. . . . . . . . . . . . . . . . . . . . . .. . . . . •. •. . . •. 1. 141 141 144 I_ .., CHAPTER VIII. 1II1C.LJ...\N.OUl aBMAILK8 UPON THE 80ua IUTUL IlO. Nebular Theory of the Origin of the Solar System, .• • • ••• • ••• •. 111. I..awa of Planetary Motion, .. . . . . . . .. . . . . . . . . ••• . .••• ..... • • • •• IIi. MiDiature Representation of the ~Iar System, •• • • • • • • • • • • • •• •• 113. Were the Asteroid8 orhdnally 0116 Planet' . . • • •• . •••• • • •••• •• •• 114. Are the Planets inhabited by RatioDal Hemp '0. .... .... ........ I. I. III 111 U8 PART 11. THE SIDEREAL BRA VENS. CHAPTER I. OJ' OONITELUTlONB OJ' ITA... J15. 116. 117. 118. 119. 110. 111. J)iatiDguishinR Characteristice of the Fixed Stars, •••••••••• •• •• Jet ~'888ification of the Stam,.. • • • • • . •• • • • • • • • • • . • • • • • • • • • • • • • • • • • • Number of the Fixed Stars........................... ~ ••••••.•• Distallces of the Stars, . • • . • • • • • • • • • • • • • • •• • • • • • • • • • • • • • • • • • • • •• Magnitude of the ~tars,.. .•. • ..•.. . .••.• . .•• . ••.•• ••••• •••.• . •• List of the Constellatiollfl. . . . •. . .• . • . • • • • • •• . . . . • •• . •• •• • . . • . . .• Description of lOme of the Prinoipal ConatellatioD8-Zodiacal 181 J83 164 . J.8I 1M Constellations... . • . . . . . . • . • . . . • . .. . . . . . . . . • . . •• • •• • • •• . . . . . . .. 170 J•• Nortllem ColJ8t~llatioD8. • •• ••• . •• ••• . •• • • • • •• ••• • •••••• ••• • •• •. 17t la. Southern CoD8t.ellatiollll, . • • • • • • • • • • • • • • • • •• • • • • • • • • • • • • • • •• • ••• 17-' 12 CONTENTS. CHAPTER II. OP DOtJ'IlU, 'YOU....,.6JfD 'l'aIlPORARY ..rAd, BlNARyanrrt:MI, ETa. LIIIon '- 114. Of Double, Triple, and Multiple Stare, .•••••••••••.••••• . •.••.. 115. Of ~jn8l'Y and ~th~r AystelJJ8, ••••••••••••••••••••••••••••••••• 121. Vantlblt' or Penodical ~tan, . . . . . . •. . . . . . . . . • . .. . . .• . • . . . . . . . .. 111. Tp.mflOrarf ~tan, ..•...•..•.....•••.....••••••••.•.••.....••..• 118. Falling or Shooting StaIB, •• , • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• •• 180 1st 188 191 lUI CHAPTER III. 01' OUJ'I'l'KU 01' 8TAJUI, AND DBt1L&. III. or CluBterw 0( Sta.m, ••••••••••••••••••••••••••••••••••••• .,... •• 114 1111. Of' Nebllle.. • • • • • • •• • • . • . •• • • . . . • . . . • . . • • •• • • • . . • • • • • • . . . •• • • •• 111 APPENDIX. 8'xplaaatioD 01 .&.troDaIDicai Tel1D8. ••• ••••• • . •• • • • •• • • •• • •• • • •• •• . . INDEX TO THE ILLUSTRATIONS. Gmat Refractiq Teleecope at Cincinnati, ~hio-troDtinl the Title; liz-inch RefractiDI Te1eecope, at Mr. Rutherford'. <>beeryatory. New York-frontiq the Preface. ftolemaic Theory or the Structue of the UDi'YeJ'B8 •••••••••••••••••• Q)pemican Theory of the Solar SJ'IIlem ..• ADpJar Meuarement- Li.ht aod Heat of the Plan... • • . • • . . • .• • • Relative Magnitude of the Sun and Planets ...••.•.•. '!be Ecliptic, Zodiac. SiPI, Nodes, Transits, &c•.•••••••• _. • • • • • • • • Zodiac, EquinOXM, SolBtices, Lo~gitude, Aecendinl Nodee, &c. •••• . '!be Earth'. Orbit. SUn'. Declination, SeaaoD8, mclination ofAxM to Orbits; and SeUOI18 of the Phmet8....... •. • . <»l\iunction, Opposition, Traasita, Phuee of VenDI, &c. •••••• • • • • • • Teieecopic Vie. . of Primary PIanef.8o. • • •• • • •• •• • • • •• ••• • • ••• •• • Batom in hi8 Orbit, Pbuea, Telescopic Vie. ., &0... •••• .••• •• • • . • • • Ph.... and Teleacopic Vie. . of the Moon...... . • • • •• . . • • • • • • • • . . • . • 0 ••••••••••••••••••• 0 0 • • •• • • • • 0 •• • • • • • • • • &c.................. the Solar and Lunar Eclipeea •• ••• • •• ••• • •• ••• • • •• • • • • • • •• ••• • •• •• • • •• •• 1'I1e PhilOlOphy or TidM. • • • • • • • • • • • • • • • • • • • • •• • • • • • • • • • • • • • • • • • • • •• Vie. . of Remarkable CoIII8IB.. • • • • ••• •• • • •• • • •• • • •• •• •• •• •• ••• • • • •• Sir Hemchel'a forty-foot Clusters of Stars, Binary ~yt4eln8, auu r'~lJule ••••••••••• Lord Rosse'lgreat Reflecting Teleecope .. William 11 1'7 33 38 49 at a • '1'1 83 ., 101 III l31 Reftector.................... ...... III 0 •• 0 ••••••• 0 ••••••••••••••••••••••••• 1~ II 181 1ft • - - - -.o;r-- - INTRODUCTION. Le880n I. IJIftOKOJIT-ITS !fANKB AS .6. ICIBIfCa. is knowledge systematically arranged, 10 . . 10 be • conveniently taught, easily learned, and readil1 applied. . .. ASTBOKolIY Is that science which treats or the names, distanoes, magnitudes, and motions the heavenly bodies -the Sun, Moon, Planets, Comett, and Fixed Stal'8 and the laws by which tbey are governed . .All who are not deprived of the ble88ing or sight have seen tae 8un, moon, and stars. Indeed they are 'Yery familiar objec».t. Now,. by carerully observing their appearance., and watohing their movements for a ahort time, every learner may discover or establish the following raot. for himself; viz. 1. The SUD and Moon appeir nearly or a size, and much lar8" than any other bodies that we see in the heavens. 2. The SUD sheds a strong and brilliant light upon the earth, while the light of the moon ia pale and Ceeble_' . 3~ The Sun and MOOD are sometimes near each other, .... when the Dew mopn is first seen in the west, wbile at other times, the moon rises hi the east just as the aUD goel down. . 4. When the Moon is first seen , east or the SUD, she i .. very alender; but as she behind and separates from the SUD, she grows larger and ]arger till ahe becomes a "full moon i" after which she grows amaller 8cIUCB or :+ ralls 2 14 ASTRONOMY-ITS NATURE AS A SCIENCE. and smaller till new moon again. The horns of the new moon point to the east, while those of the old moon point to the west. 5. It is easy to 8ee, by watching the moon tor only Qoe or two nights, that she is actually moving eastward 8S respects the stan; and she sometimes runs over, OJ' seems to cover up one, and" put it out for a.time as she , goes along. 6. Everybody has notioed the dark linea and spots upon the surtaoe of the Moon, as if some one had at. tempted to draw an outline map of some new country upon her face, showiDg its various islands, continents, and seas. . 7. Moat people have seen what is called an ~clip8e ; or in other words the "partial or total darkening of the lun or moon, as if some large" objeot was covering . them up. " 8. The stars difFer very much in their p.pparent sizesome appearing large and bright, while others are 80 small and taint as to be 8carcely' perceptible. 9. Most of the stars seem to" keep the sam~ ,distanoe from each other, and to ocoupy the same positions with reference to each other from age to age. But there are a few that are constantly wandering along eastward, as it were trom star to star,. till, like the MQOD, they traverse the whole circuit of the heavens. Dl&ring this journey, they sometimes stop for a while, and even fall back west.ard, but they soon resume their ..route again with an accelerated motion, and hasten eastward over the celestial concave. 10. One star at least is west of tbe sun Cor a time, and rises beCore him, «;>n which account it is called the Morning -Star. But this same star, may at other times, be seen east of the SUD. At this time sne may be sp-en in the west after the SUD goes down, and is then called the Evening Star. 11. The .stars in the northern portions of the heavens aeoer Bet, but seem to revolve around what is called the North Pole star, from night to night, and from year to year. By ranging by a stake or some other permanent ,. " ~ '-~ .ANCIENT HISTOB.Y 0., AITKO.OIIY. 15 object, on a clear evening, it will be seen in a sbort time. that all the stars below the North Pole star Beem to be moving euttDard. 12. During the winter, the sun is quite low down in the south; but in June and July, he is almost directly overhead at twel ve o'clock, even as fa r north 88 the United States. These, and maDY otber curious things respecting the heavenly bodies, may be observed with the naked eye, or without the aid of telescopes. It was in this way that the ancients studied astronomy. By oarefully watching the heavens, they learned ODe fact after anQther, respecting the SUD, mOOD, and stars, and when these facts were put together and arranged in systematic order, they constituted the Science oj .A6~ Lesson ~. ANCIENT HISTORY OF ASTRONOMY-TBE PTOLEMAIC THEORY. (Map 1.) The oldest records of astronomicai science are found in the Holy Scriptures. We there read of the creation the sun, moon, and stars, and thf' commencement their revolutions. In the Book Job, which was written fifteen hundred years before Christ, we read of "Arct,,nu, Orion, and Pleiades, "-stars or cl usters of stars that bear the same name ~t the present 'day. Weare here taught, also, that our world does not rest upon some vast and strong foundations, but that the Almighty " hangeth the earth upon nothing." The prophet Amos speaks of the "seven stars and' Orion." 8ev~n hundred and thirty-three years before · Christ, and of the phenomena of day and night. The Greek philosopher, Pythagoraa, taught astronomy about five hundred years before Ch rist, and the Egyptian philosopher, Ptolemy, in the second century of the Christian era. Ptolemy constructed a regular system or theory of Ifstronomy, by which he proposed to account 'for all the appealrari~. and motions of the heavenly bodies. ' or or or "f • , '1 16 I TIm l'TOLBIU.IC TBBOllY. The PTOLBIIAIC SYSTDI, 80 called from Ptolemy, its author, is the subject of Map No.1. It represents the earth as located in the centre of the universe; as being perfectly at rest; as a plane instead oC & globe; and as inhabited only on one of its sides. Some supposed die . earth to float upon an abyss of waters; while others be. lieved that it rested upon the head of an eOQrmous serpent or dragon, as represented on the map. Ptolemy taught, .190, that) the 8UD, mOOD, planets, and stats revolved around the earth, frOID east to west, as they appear to do, every twenty-four hours. To account for their passing over the earth without falling down upon its surface, it was supposed that the heavenly bodies were supported by vast arche8 or IwllorD aph,ere" in which they were firmly .et like a diamond in a ring. But "as the SUD, moon, planets, and stars were not a11 at the same distance from the earth, it was supposed that there were several of these spheres placed one above another-that the Moon was in the first, Mercury in the eecolld, Venus in the third, the Sun in the fourth, Mars in the fifth, Jupiter in the sixth, Saturn in the seventh, aod the Fixed Stars in the eighth. The anoients had no knowledge of Herschel, or Le Verrier. Mercury, Veo'us, and the Moon, were placed in the three lower spheres, because they were sometimes seen to pass between the earth and the sun. But Me.rcury aDd Venus sometimes go before the sun, and sometimes follow after him. To account for this" it was supposed that besides the great circle of the heavens around w hioh they passed daily, they had other smaller circles withiD their respeotive spheres, in . which they revolved at the same time. These the a!1cients called ~lu. They may be seen on the Map, In the second or sp_ of Mer. oury. To acoount Cor the rapid westward motion of these ponderous spheres, it was believed that the neceSS81 y moving power was applied in some way to the upper sphere, above the fixed stars; and that this sphere COAlmunicated its motion to the ODe immediately b,e.neath OJ within it, and 10 on down to the lower sphere. !fhis, h 17. DIPPICl1LTIBS OP TBB PTOLEMAIC TBBO.Y. # was thought, moved slower than the rest, .s the mOOD or • constantly fell back of the SUD. To allow the light the stars to pass down to the earth, it was supposed that the sever~l concentric spheres rising one ah9ve another, were made of the finest cry,tal, and were perfectly transparent. The space above the fixed stars was designated as the blissful abode of departed spirits. On the map, the spaces between the white circles represent the several crystalline spheres. The sun and mOOD are represented as going ~own in the west, 'he mOOD baving fallen a little behind the 8UD, as when we first see the new moon. Mercury and Venus are near the SUD, &I they always are, and Mars, Jupiter, and Saturn on the left. On the right "is seen a comet passing down toward. the sun. Such is the Ptolem4ic TMDrJ of the structure the Universe. or Lesson 8. DIPPIC11LTIBS OP THE PTOLBMAIC TBKOB.Y. (Map'l.) Besides the 01 umsiness of the machinery, it W88 at. tended by numerous difficulties :which ita supporters could Dever explain or obviate. ~ 1. It could never determine what upheld the earth. Rooks and mountains could not float upon water; and if they could, what upheld the water' Some imagined that the earth was upheld by a huge 86r:JJe"', resting upon the back of a tortoise, as represented in the map. But what upheld the tortoise' 2. It represented many very large bodies, &I the SUD and some the planets are DOW known to be, as revoly. ing around the earth, a com'paratively small one. a. It adopted the most difficult and unreasonable plan for lightipg and warming the earth, and producing day and nig~t: - Taking the sun around the earth every twenty-four houra, W88 like carrying a fire around a or 2- 18 TBB COPBllMICAN STInK. • person who was cold and wished to be warmed; instead of his turning himself to the fire as he pleased. 4. The Ptolemaic theory would require a motion inoonceivably rapid in all the heavenly bodies. As the aun is ninety.fi ve millions of miles from the earth, the entire diameter of his sphere would be one hundred and ninety millions of miles, and its circumference about six hundred millions. Divide this distance by twenty.fourthe number of hours in a day-and it gives tUJent,-fifJ, aillion "tile. aft hour; or sixty-nine thousand four hundred and Corty. four miles per second, as the velocity oC ahe sun! " This theory gi ves a still more rapid motion to Mars, Jupiter, Saturn, and the fixed stars. It would require the nearest of the latter to move at the rate or near four- . "m thouBand milliO'll,8 of mile. per a6corul, or seventy thousand times as swift as light, in order to accomplish ita daily course. But with all these difficulties in its way, the Ptolemaic theory was generally believed till about the middle oC the .ixteenth century, or three hundred years ago. Lesson 4. THB COPERNICAN SYSTEM. (Map S.) or or About the year 1510, Niclwlatu Copernicu, Pru88ia, . taking some hint perhaps from the writings p,tIaogo. ru, discovered what is now generally received as the true theory of astronomy, and called aft~r its author the Corpemican Syatem. The COPBRNICAN SYSTBM attributes the apparent daily motion of the sun, moon,. and stars rrom east to wes\, to the actual motion of the earth on its axis from wes' to east. Though the heavenly bodies ,ee". to move; yet we often transfer our own motion, in imagination, to other bodies that are at rest; especially when we a~ oarried "apidly along without effort, u in a carrisge, steamboat, ". \ 1 n_IT a_AXD DmSIOX8 01' TID VKIV..... 19 or railway car. It places tbe SUD in the centre or a ayatem or worlds, of which the earth is one. It gives thel'll a reyolutioo around their common centre, by which the 1888008 are produced; and anbther upon their axes, producing day an~ night. It accounts tOr all the motions of the heavenly bodies, and harmoniu. the whole system of aature. The C~" S,.tem is represented in Map~. ID the centre is seen the sun, in a state or rest. Around him, at unequal distances, are tbe planets and fixed stars, the rormer revolving about him (rom west to east, or in the direction of the arrows.- The white circles represent the oriJiU, or paths, in which the planets move around the SUD. On the right is seen a CMMt plunging down into the system around the 8un, and then departing. This is the Copernican Tl&eory or the 101 ar system. M 0 how ualiJr.e the complex work. 01 man, Heaven'. euy, artIe88, uaeDcwnber'd phAD!" The truth of the Copernican theory is established by the moat conclusive and satisfaotory e~idence. Eclipses the. sun and mQOn are calculated upon this theory, aDd astronomers are able to predict thereby their com. mencement, duration, &c., to a minute, even hundreds years before they occur. We shall, therefore, asBurne the 'ruth or this system, without further proor; and proceed aocordingly to the .tudy ot the hoavenly bodies. or or Lessen ~. )'laST GRAND DIVISIONS OF TO TINIVBBSB. (Map 2.) The material universe may be divided into two parts, viz., the SOLAK SYSTBM and. the SIDEREA.L HBA VENS. The Sol4r Sy8tem consists of the Sun and all the planet. and comets that rp-volve around him. The Siti8real HeaDeR. em brace all those hodiel that • 20 PIEST GEA.lfD DITISIONS OF 1'HE UNIVERSE. or \ lie around and beyond the solar system, in the region the fixed stars. Th,e relation of the one to the other may be partially underst~ by carefully observing Map 2. The sun and his attendant worlds are there seen tDithin the fixed .tars, which occupy the corners of the map, and the spaces without in every direction. If' the observer were placed at a distance beyond the solar system, in any direction, he would see vast numbers of the fixed stars between it and him, as if they were scattered between the eye of the learner and every part of the mnp. But situated 88 we are, in the mi8st of the Sidereal Heft vens, which surround us in every direction, it is not strange that the earth should seem to be in the centre of 'the universe. In considering the genera:l fJubject of astronomy:, we .ball proceed according to tbe foregoing classifica'ioD, treatiug first of the SOLAR SYSTEM, and seCQ¥1y, of the 5mBREAL HBA.VENS. .~ . . .. \ .. 1 -.-.!- PART I. OF THE SOLAR SYSTEM. CHAPTER 1• . CLASSDTCAnON or THE SOLA.R BODIES. .fBB S11J(, PUNBTS, PllI14A.BtIES, SECO.NDA.KIBS, k. (Map 2.) Solar System d.,ives its name (rom the Latin word Sol, the Suo. It Includes that great luminary, and TUB '. all the worlds that revolve around him. To distinguish these attendant bodies from others in the heaveDs, the, will be denominated Solar Bodiu. The bodies the Solar System are divided into sey. eral distinct classes. I. The SUN is the fixed centre of the system, around which all the solar bodies revolve; and from which they receive their light and heat. . II. The PLA.NETS Bre those bodie. that revolve around ,the 8UD, and receive their light and beat from him. The t term p14ttet signifies a flNl,nderer, and was applied to the. IOlar bodies because they seemed to move or waDd~r about among the stars. ~. 1. The planetS are divided into Prima,., and SecoiadtJ,., planets. The primary planetA are those larger bodies of the system which revolve around the SUD only, as their cen. tre of motion. They may be distinguished on the map by their size,. and also by tbeir being in their orbits, or OD the white ciroles. . or 6 22 '~AXES AND SIGNS OF THE P.IJlARY P~NBTS. The 8f.Condary plane" revolve not only around· the SUD, but also around the primary planets, as· their attendants or mOODS. They: may easily be distinguished . on the ·map. 2. The planets are again divided into lnUrior and E~ ~rlor planets. The interior planets are those whose orbits lie II1ithi" tbe orbit of the earth; or between it and the SUD. The ezt.erior ,lonets are those whose orbits lie tDithout the orbit of the earth. 3. Five of the smaller primary planets are called. ABteroid8. They may be seen on the map near together, just above the SUD. 4. C~et8 are a singular class of bodies belonging to the solar system, distinguished by their long flaunting trains of ligbt, and also by the elongated form of their orbits. CHAPTER II. OF THE PRIMARY PLANETS. Lesson 7 • • A.MBS AND SIGNS OF THE PRIMA.RY PLA.NBTS. (Map 2.) . TUB Primtlry Planets are thirteen in number. They are distinguished in a8tro~lomical books by certain characters or signs, which are· llsed to represent their respective planets. The names of the planets and their symbols are as follows: * · Mercury, ~ Venus, ~ Earth, ED Mal'll, 3 ~S l a Vella, Astne&,· JUDO, *0 ~ ~ Cere., Pallas, Jupiter, SatW'D. Herschel, Le Verrier, • Four new Asteroida have recently been discovered, of which, however, very little i. known. They are called Flora, Iris, Met,., and Hebe. . • • • , K£JIBI AlfD SlSKI 0,. TIIB HOUBY PLAN.ft. Most or the J(oddesees. MBBCUBY sign, ~, is around it. VBNUS 23 planets are named after heat.hen gods or was the meuenger or the gods, and the his CtUluceu, or roll, with ,~rptfIU twined was tbe goddess or tOTe and beauty. Her is a fAirrot' with a handle after the ancient sigOt ~, form. The EARtH is repreaented by the sign a, denotinll a BpAere and its equa.tur; or by $, which may denote either meridiana of longitude, or the four quarters of the globe. . . MABs wu the god of war, and hil sign, I, is a buckler and rpefl-r •. VESTA, the goddess 01 fire, hu the sign of an altar, I, with a fire blazing upon it. ASTR.&A, the name of the new asteroid, signifies a ,tar, and may. l»e known by its appropriate sign, JUNO was the reputed queen of heaven; and her sign, C, is an ancient mirror, croWDed \vith a ,tar-an emblem of beauty and power. CERES is 80 called after the goddess of grain and har. vests. Her sign, ~, is a ,ickle, of an antiq uated form. PALLAS was the goddesa of Wiadom, and her sign, 9, is tAe head of (J rpear. J trPITER, the reputed father of the gods, is known by the sign 2l. It was originally the letter Z, the first letter of the' Greek word Zew, the name (or Jupiter, which has been changed in the coune of time to its preseDt form. SA-T11B.X was the reputed father of Vesta, Ceres, &0. His astronomical sign, 'J, is supposed originally to have denoted a .cytAe. HERSCHEL, 80 called after Sir William Herschel, ita discoverer, (also caUed Georgium Sida, or GeorKi!zn Star, after George III. his patron, and Uranu8, (rom a heatheD divinity,) has the sign of the letter H, with a planet suspended from the cross-4)ar-thus, '&I. It is designed to indicate Dr. Herschel afl its discoverer. La VBBRIEJl, the last nefD planet, sci called from its di.. *. I I 24 • .a.Ka A.XD .Ia•• OF TIlE oo~erer, PIlI.AllY PLUf.T8. hu the sign of an L and a V' united, with a planet suspended from the hair line of 'he V-thus, 14,·. This al80 denotes the diacoverer of ~"e planet.· The MOON is denoted by various signs, according as it is new, half.grown, or full-thus, e, 1>, O. The SUN is represented by the sign 0, deuoting an aocient Insckk,.. As the aDcients kept their bucklers brigh~ 80 as to dazzle the eyes of their enemies, this iostrumeDt was selected as the appropriate emblem of the 8UD. It is also known by the signs t!b and The five plan eta enclosed in braces in the" table are the .A8teroitU.· Mercury and Venus are tbe ir&terior planets, and those outside the Earth's patb the ezIerior. The several planets should now be looked out UPOD the map, and' their comparative size" rlistances from the 8Uft, and appearances carefully noticed. MercurJ is placed close to the SUD, and directly under him. Vemu is 8180 near the SUD, and a little above him on the left. The EartA is next in order, above the SUD, and a little to the right. The Moon and her orbit will be seen near the earth. Mar8 is aD the right of the SUD, and beyond tbe orbit of the eartb. He 'is the irst of the nor planets. .A. bove the earth are seen the five planets called .A,rteroida, viz.: Vt8ta, .A8trtla, Juao, Ceru, and Pallas. Jupiter is tbe large planet below the 8UD on the left. His surface is striped with· ourious '6el,., and he" . is attended by (our secondary planets or moons. A bove the Asteroids on the right is seen the beautiful planet &dum. He is attended by Beven moon~ and 8urroundei by two ~ magnificent and wopderful ring.. Her.c1&el and his six moons are ~1Q.ced on the left, near the upper comer of the rnll p. Le Verrier could not be placed upon the map at his relative distanoe, but may be imagined at twice the distance of Herschel, and of about the same magnitude. , e. "Ie- • The Board of Lo.,;tude of Parie I'8COIDIDeDd that the IMW after the heathen pel the lieU, with we see no good re.,n why th" Dame of ... discuverer should be exchanged for that of aD imuginary divinity. AstronomJ BI'eda DO additioaal appenda,.. from the MytholUQ p1ane~ be cat.llecl Neptu".., the Bigll of a trident; but 01 t"~ aDcieDta. or .. DISTA.NCES 0. THB PUNBT8 LeS80R Fao. TID aUK. t6 S. DISTA.NCBS OF THB PLANETS FROM TRB al1K. (Map 2.) Map 2 shows all the planets, except Le Verrier, at their relative distances from the sun. 'rhe scale is one hundred rn ill ions of miles to an inch. The distaDoes of &he planets in Iniles are as follows: Ceres" 263 millions. Mercu."y, 37 millioo!. V en us, 69 " Pallas, 263 " Earth,· 95 " Jupiter, 495 " Mars,· 145 " SatuFn, 900 " Vesta, 225 " Herschel, 1,800 " Astrrea, ~53 " Le Verrier, 2,800 " JUDO, 254 " It is difficult to conceive justly of these vast distances. Were a body to move at the rate of five hundred mile. an hour, without intermiSliioD, it would require near eight and a hal f years for it to pass from the sun to the nearest of these planets. To visit the flarth would require over twenty-oue years; and to reaoh Herschel over four hUDdred years! . Railroad oars travel at the rate of- about thirty miles an hour. or a mile in two minutes. Now if there was a railroad froln the sun to the orbit of Le Verrier and the orbits ~ the other planets were stopping-places 00 the route, the train would reach ' Meroury, in 152 yea .... V en U8, " 264 " . Earth, "381 " Mars, "554" Jupiter, "1,884 " Saturn, "3,493 " Herschel, "6,033 " La Verrier, u 13,700 " Such a journey would be equal to riding 900,000 tim. a 26 DEGRBBS, MINUTES, A.ND SECONDS BXPLAINlbI. over Whitney's proposed railroad from Boston to Oregone It is now about 5,850 years since the creation of the world. Had a train of cars started from the sun at that time to visit the orbit of Herschel, and travelled day and night ever since, at the rate of thirty miles per hour, they would still have 284 millions of miles to travel before they could reach their journey's end. To finish the passage would require 1,083 years longer; the whole of time past and a thousand years to come! To reach the distant orbit of ~e Verrier the train would need to proceed onward, at the same rapid rate, nearly 7,000 years longer! Such is the vast area embraced within the orbits of the planets; and the spaoes over which the sunlight travels, to warm and enlighten its attendant worlds. Lesson 9. I)BGIlDS, IttJNUTBS, AND SECONDS EXPLA.INBD. (Map 3.) . .. In astronomy, the distances and magnitude of bo~iel are often given in degrees, minute., and ,eeCJ'lUl8. It will be necessary, therefore, to show what these mean. ~,.'t "A circl.e is a plane figu1'~, comprehended by. single curve line, oalled its circumference, every part o£ *tWhich . is equally distant from the point within called its .eeht'.:e." A ci rcle is represented on the right at Fig. 1. . A q,/,adrant is the fourth part of a cirole. A sextant is the sixth part of a circle. A Bign is the twelfth part of a circle. A degree is the thirtieth part of a. sign, or"one three hundred and sixtieth part of a circle. · A minute is a sixtieth part of a degree; and . A ,eeond. is the sixtieth part of a minute. On the map the circle is divided off into parts of ten degrees each, and numbered in figures every thirty· degrees, or oftener. It· will be seen that one.fourth of a • • ·1 .A.KGULAJl DISTANCES, KAGNITUD• ., BTC. 27 lit"', oil ~le contains just tAree riga, or aitlet, tlep. . ; and half a oircle U 1igM, or mAe AUflued, and tkgrea. All oircles, whether great or small, have the same Dumber of degrees, namely, tJiree hundred and sixty. But one hundred BDd eighty marks the greatest possible angle, as a pair of compasses can be opened DO farther than to bring the legs in a straight line. These degrees, &0-., are used to represent the angle which any two linM form, coming from different points, and meeting at the eye in the centre. In the figure the lines passing from the stars on the left to the eye, are found by the measurement OD the oircle to be ten degrees apart. If the dotted liDe was perpendicular to the lower or plain one, they would be ninety degrees apart, &0. Degrees, minutes, and seconds are denoted by certain characters, as follows: 0 denotes degrees, ' denotes minutes, and" denotes seconds. Thus, 100 15' 20" is read ten degrees, fifteen' minutes, 8Dd twenty seoonds. Measurement by degrees, minutes, and seconds, i8 called .Angular MetUUrement. Lesson 10. AKGULA. DISTA.NCBS, MA.GNITUDES, &0. (Map 3.) In Fig. 1, the observer is represented 8S seeing two stars on the left side of the map. By looking at the graduated or divided cirole, it will be seen that the angle which these two stars make at the eye is 1Oc:>. The stara are therefore said ..0 be 100 apart. If a globe filled the same angle, or number of degrees, as shown on the map, we should say it was 100 in diameter. If the_~pace be. tween the foot of a mountain and its top -filled the same angle,' we should say it was 100 high;' and if a comet passed through the same -angle in one hour, we should 8ay its velocity was 100 an hour. All circles, whether large' or small, have the sameDumber of degrees j but the angle which an object makea 28 THE Stnf AS SBBN PROM THB DIFPERBNT PLANETS. at the eye will be great or small, according as it is Dear to or di:ltant from the observer. This is illustrated by Fig. 2. On the left is the object. To the observer in the centre the globe is 200 in diameter; but to the one on the right its diameter is but 10°. To a third observer, at twice the distance of the last, it would appear but 5° in diameter, &0. This sho~8 why objects, grow smaller in appearance as we recede from them, and large.r as we advance towards them. Their apparent magnitude is in. creased or diminished in proportion to the distance frtmj .ldeA they are "ielDea. Lesson 11. THB SUN A.S SBEN FROM THB DIFFBRENT PLA.NETS. (Map 3.) By the' table of distances, (8,) and also by Map 2, it will be seen that the Sun is about twice as near to Mer. cu ry as he is to Venus. Of c'Jurse, then, according to the principle illustrated in Fig. 2, his apparent diameter must be twice as great when viewed from Mercury as . when viewed from Venus. From the Earth it is still Rmaller, and so on till we view him from the distant orbit or Le Verrier, from which he would appear but a small glimmering point in the heavens. Ftom the fixed star Sirius, he would" appear smaller than Sirius appears to us. The relative apparent magni'tude oC the' Sun, as seen Crom the ditfeI:ent planets, is represented by Fig. 3. His angular diameter would be, From Mercury • • " " " .," II /, Venus Earth Mars '" Velta Astrma Juno • S!f • • • 4 • • • 32' • • 21' ' . . . lSi' • • • 12' - - • 12' · lit' From Ceres. - 11 ' " Pallas ... Jupiter 6' " "u Saturn . . . Herschel. " Le Verrier • 50" ~: • PHILOSOPHY OF THB DIFFUSION OP LIGHT. 29 From Mercury it is supposed that the spots OD the SUD would be visible to the naked eye, as seen on the map j and from Le Verrier the Sun himself wquld appear but as a large and brilliant stl1r. Let the student imagine him. self as approaching the SUD till it has four times its present apparent diameter, and his spots stand out in full view to the naked eye; and then let bim recede from the sun, pass the earth and the orbits of Jupiter and Saturn, and retire away into space, till the SUD appears but a glim. mering star, aod he will have lOme raint conception of the almost inconceivable. distances of the 801ar bodies. Lesson I". PHILOSOPHY OP THB DIFFUSION OP LIGHT. (Map 3.) Light always !Doves in straight lines, unless turned out of its course by reflection or refraction. This is repr~. sented by Fig. 4 on the map; where the light is seen passing to the right, from the SUD on the left. From this law it follows that the squares A B and C in the diagram • wou Id receive equal quantities of light; but as B has four times, and C nine times the surface of A, a single square of B equal to A,- would receive only one.fourth as much light as A; and a square of C, equal to A, would receive only one.ninth as muoh. This difference in the amount of light received is caused by the unequaJ di8f.ance8 of the several squares from .the miniature sun on the left. The distances are marked on the upper line of light by the figures 1, 2, 8. The rule for determining the relative amount of light reoeived by several bodies, respectively, placed at llD6(lUlll distances from their luminary, is, that their light i8 'flfJer8ely Q,8 the aq'llare8 of their diatancu. This rule, al80, is illustrated by the figure. The sq ua~e of 1 is 1; the square of 2 is 4; and the square of 3 is . 9. Hence 1., f, and 1-, will represent their relative light, as already .hown. The checks are designed to illustrate this. .ole. a* • 30 LIGHT A.ND HEA.T OP THB SEVERAL PLANBTS. Lesson "13. LIGHT AND BEAT OF THE SEVERAl. PLANETS. (Map 3.) By applying the foregoing rule to the planet8, at their nlapecti va distances from the SUD, we are enabled to 8.Hcertain the relative amount of light received by each; and on the supposition that their heat is proportionate to their light, we can easily determine their a"erage tem. perature. At the bottom of the map the planets are placed at their relative distances from the SUD, QOmmeocing with Mercury on the left, and extending to Herschel on the right. Immediately over each planet respectively, and near the upper line of the diagram, is marked the proportionate light and heat of each, the earth being one. They are as follows: 6t Mercury. • - • - V en us - - - - • - • 2 Earth - - • • - - - 1 Mars. - - - - - - Vesta - - • • • - Astnea • - - - - • t t 1 uno· - • • - - • Ceres and Pallas. - I . 1 upiter - • - - - - -1Y Saturn • - - - • - -h Herschel • - - • 111 Le Verrier - - • rho . It appears, therefore, that Mercury bas 6! tim~s as much light and heat as our globe; Herschel only and Le Verrier only...-Jn.nth part as much. Now' if the average temperature ilie earth is 50 degrees, the average temperature of'Mercury would be 325 degrees; and as water boils at 212, the temperature of Mercury Inust be 113 degrees above that of boiling water. Venus would have an average temperature 100 degrees, whioh would be twice that of the earth. On the other hand, Jupiter, Saturn, Herschel, and Le Verrier, seem doomed to the rigors of perpetual winter. Think of a region 90, 368, or 1300 times colder than the average temperature of our globe I m, or or I XA.GNIT17DB OF THB PLANBTS. II 31 Who there iDhabit must haYe other powen, Juices, and vew, aDd 1eD88, aDd life, thaD OUN: Oue momont'. cold, like thein, woold pierce the beme, Freeze the heart'. blood, aDd tura u all to Itou.e !" It is not certain, however, that the heat is proportionate to the light received by the respective planets, as variou local causes may conspire to modify either extreme of the high or low temperatures. For instance, Mereu". may have an atmosphere that arres~ the light, and screeD. the body of the planet from the in8upportable rays of the SUD; while the atmospheres of Saturn, Herschel, &0., may act as a refracting medium to gather the light (or a great distance around them, and concentrate it upon their otberwise cold and dark bosoms. . Lesson 14. JUGKITUDB 0,. THE PLAlfBTS. (Map 2.) On the la~ge map the planets are drawn upon a seale of 4:0,000 miles of diameter to an inch. The Sun is represented as but a point, because he could not be placed in the map, of a size proportionate to the planets. The diameters of the several plane~ are as follows: Mercury, 3,000 miles. Venus, 7 2800 " Earth, 8,000" Mars, 4,200" Vesta, 270 u Astrrea, unknown. . Juno, 1,400" Ceres, Pallas, Jupiter; Saturn, Herschel, Le Verrier, 1,600 miles. 2,100" 89,000" 79,000" 35,000 " 35,000 " By carefully obse"ing each planet as laid down on the map, it will be seen' that their relative magnitudee correspond with their relative diameter. as bere stated. , • 32 aBLATIVE XAGNITUDB OP THB SUN AND PLANBTI. Lesson 13. 1lBLATIVB MAGNITUDE OF THE SUN AND PLA NE;TI. (Map 4.) The relative magnitude of the sun and planets E repre:sented in Map 4, Fig. 1. The scale of the charts is the same as in No. ~-Damely, 40,000 miles of diameter to an inch. As the sun is 886,000 miles in diameter, he is drawn 221 inches across, to show his true magnitude as compared with the planets. These may be seen on the right side of the m~p, commencing with Mercury at the t01>, and passing downward to Herschel. La Verrier is opposite Herschel on the left. Thp. seeondary planets will be seen around their primaries. . The magnitudes of the primary planets as compared with the earth, are as follows, viz. : n Mercury, • • - Venus, • - - - • Ii Earth,. • •.• -. 1 Mars, - • • • •• Vesta,. - - _. i I 0 0 0 Astrlea, unknown. Juno, - • • - - • rh . t (Jeres, • - - • .Pallas, • - • Jupiter, - •• Saturn, •• Herschel, _. • 11t. • -h 1,400 1,000 Le Verrier, - 90 90 The BUft is 1,400,000 times larger than the earth, and 500 times larger than all the other bodies of the Solar System put together. It would take one hundred and twelve such globes as our earth, if laid side by side, to reach across his vast diameter. The moon's orbit is two hundred and lorty thousand miles from the earth. N o~, if the sun was placed where the earth is, he would fill all the orbit of the mOOD, and extend more than two hundred thousand miles beyond it on every side! What is a globe like ours compared with luch a vast and ponderous body as the SUD' ~ " " l eOllP~.~TIT. DBNIITY 01' TD PLANETS. 33 Lesson 16. COlllPAKA.TIVB DENSITY OP TBB PItANETI. 8y deMity is meant compacme.8 or clolene8•. of ptJ,:,.. Hence we say cork is less dense than iron, and Itone ia more dense than common earth. In like manner the plane~s differ from each other in density, or in the compaotn~8S of the substanoes of which they are composed. The comparative density of the I8veral planets, and tbe eubstances with which they most nearly agree in weight, will be shown by the following table, in which the earth fa taked as the standard of camparilOn. Mercury, •• 3-lead. Venu&, • • • 1'. earth. Earth, ••• 1 Mars, ••• h--earth. Jupiter, Satum, ••• Herschel, • La Verrier,. Sun, • • • • ,Jo-cork. l~water. unknown. l-water. •• i-water. This table is one of cODsiderable importanoe, and .uld be com~itted to mem~ry. Ita uses will be more clearly see.n in the ~ext lesson. , Lesson 17.' MrTJlA.CTION OP TBB PLAKBTS. Attraction or gravitation is the ten.denoy of bodies to1Fards each o~.~¥r, \ By this i?Buence sub~tances fall to . the earth, wb@n raIsed from It and left WIthout. support. The force of 'attraction is what constitutes the !Deig"t ot Ilodies; and its amount depends upon the q u&ntity of matter in the bodies attracting, and their distances from each other. . From the above law of attraction it follows that large bodies attract much inore strongly than small ones, pro.. Tided their densities are equal, and their distances the same; and 88 the force of attraction coDstitutes the we;'''' .' I 34 ATTUCTION O:r THB PLANBTS. of a body, it follows that a body weighing a given number or pounds on the Earth would weigh much more on J u. piter or Saturn;, and much less on Mercury or the Asteroids. The following table shows the relative attractive force . of the Sun and Planets. A body weighing one pound 00 the Earth, would weigh • On Mercury, " " " " " " " Venus, • Mars, Jupiter, • Satum, • Herschel, Le Verrier, The Sun, • • lb.. os. 0 0 0 9} 15 2 • • • • • • 8 8 1o 125t unknown. 28 5) A· person weighing 150 lbs. on the Earth, would con.. sequently weigh 375 Ibs. on Jupiter; 4,250 lbs .. on the SUD_; and ol1ly 75 Ibs. on Mars. The attractive force or the Asteroids is 80 slight that if a man of ordinary muscular strength were transported to one of them, he might probably lift a hogshead of lead from its surface without difficulty. But the learner will notice that the attractive force, as shown in the above table, is not in strict proportion to the bulk of the planets respectively. This difference will be accounted for by again referring to Lesson 16, where the subject of deMit, is considered. From the principles there laid down, it will be seen at once that though one planet be as large again as another, still, if it were but half as den~e, it would contain no more matter than the smaller one; and their attractive force would be equal.If' Jupiter, for instance, were as dense as the earth, his attractive force would be four times what it now is; and if the density or all the· solar bodies 'Yas precisely the same, their attractive force, or the weight of bodies on their surfaces, would be in exact proportion to their bulk. . . .IODle UTOL11'l'IOKI 01' 'I'D PL.lKftB. 3ti Lesson 18. 'BllIODIC eVOLUTIONS o:r THB PL.llfa'S. (Map 2.) It has already been stated (3, 4, and 6) that the planet. revolve around the sun. Their direction is from welt to east, or towards that part of the heavens in which the SUD rises. The passage of a planet from any particular point in its orbit, around to the same point again, is called it. periodic ref'olution; and the time occupied in making suoh revolution is called its ptriodic time. The periodic times of the planets are 88 follows: Mercury, • Venus, • Earth, • Mara, • Vesta, • Astnea, • Juno, • Ceres, • Palla., • Jupiter, Saturn, Herschel, • Le Verrier, • • 0 • • • • • 1 1 '" 8 4: 4: 4: 4: • • • • • • • • • o years, • • • . 11 • 29 • 84 • 164 " " " " " " " 88 days 225 822 230 51 131 " " " " " 222 " "cc· " 222 317 " 175 " " " " " The periodic tio18 of a planet may very properly be oalled its ,ear; hence, one of Herschel's years would equal 84 of ours; a year of Saturn is equ\ to about 30 of ours, &0. But this differenoe in the length of the years or the aeveral planets, is not owing .solely to the difference in the extent of their orbits: there is an aotual difference in their velocities, 88 will be Ihown in the next 1818OD. a6 CBNTKIPBTAL AND CBNTRIFUGAL FORca. Lesson 19• . HOURLY MOTION OF THB PLANBTS IN THBIR ORBITS. , (Map 2.) Mercury,. • 96,000 miles. Venus, • • 75,000 " Earth, • - 68,000 " Mars, • 55,000 " Ve8ta, • - 44,000 " Astnea,.. • 42,000 " Juno, •• • 42,000 " Ceres,.. 41,000 " Pallas,.. 41,000 " Jupiter, • • 30,000 " Saturn, • • • 22,000 " Herschel, • 15,000" Le Verrier,. • • 11,000 " Here, instead of finding the swiftest planets perform. ing the longest periodic journeys, this order is reve rsed, . and they are found revolving in the smallest orbits. The Dearer a planet is to the SUD, the more rapid its motioll, ud the shorter'its periodic time. The reasons for thia dift"erence in the velocities and periodic times of the planeu, will appear i~ the next lesson. it Lesson ~O. CBNTRIPBTAL AND CENTalFUGAL poaCBS. (Map 2.) The tendency of the planets towards the sun, or in other words, the mutual attractive force of the sun and planets, is called the centripetal force; aqd the projectile -force, or that which impels the planets cfnward in their . orbits, is called the centrifugal Coree. If the centripetal, or Coroe of attraction, was suspended, the planets would DIURNAL Jl&VOLl1TIONS 0., TUB PLANBTS. 37 lIy off in straight. lines beyoDd their present orbits, and leave .the Solar System forever; and if the centrifugal force was suspended, the planets would yield to the oeDtripetal force, and fall to the surface of the sun. It has already been stated, in Lesson 17, that the force of attraction depended somewhat upon the distance8 of the attracting bodies; those nearest together being mutually attracted most. It follows, therefore, that ~Iercury has the strongest tendency towards the sun, Ven us next, the Earth next, &0., till we get through to Le Verrier; and as the centrifugal force, which is to balance the centripetal, is created by the velocity or projectile force the planets, that velocity must needs be in proportion to their distances respectively, from the sun; the nearest revol ving the most rapidly. This we find to be the actual state of things in the Solar System. And what wisdorD and skil.l are displayed in so adjusting these great forces,. as that the planets neither fall to the sun 00 the one hand, Dor fly off beyond the reach of his beams on the Mher! AI it is, they remain balanced tn their orbits; and steadily revol ve at stated periods from age to age. "0 Lord, how manifold are thy works! in wisdom hast thou made them or all." . Lesson ~1. DIl11I.NAL REVOLUTIONS OF THE PLANBTS. (Map 8.) In addition to the motion of the planets in their orbit. tiround the sun, they have another motion around their respective axes, producing the vicissitudes of day and night. So far as is known, the time of these revolution., or the length of their days, respectively, is as follows: 24 hours. Mercury, • • • • Venus, • • • • • 231 " Earth, • • • • • • 24 " Mars, • • • • • • 24! " Jupiter, • • • • • 10 " Satum,. • • • • • 4: 101 " 38 • { TRUE -PIGl1JlB OF THE PLANETS. Hersche1, • • • •• u,nknown. Le Verrier, • • • • unknown. Sun, • • • • 25 days 14 hours. The learner will not fail to observe the striking simi. larity in the length of the days of the first four of the planets; much less the very rapid motion of Jupiter and Saturn upon their respective axes. As their days are only about five hours long, the, sun must seem to mount very rapidly up their heavens, and to decline as rapidly downward to their western horizon. His progress must be apparent to the inhabitants of those planets. From the rapid, rotation of Jupiter and Saturn, it follows that they must have about 875 of their days in" one of our years; and as Jupiter's year is about 12 times, and Saturn's about 30 times as long as ours, it follow& that the former will have about 10,500 days in his year.. . and the latter about 26,200. ' The fact that the planets revolve upon their respective axes is ascertained by observing the motion and direction of spots on their snrfaces; or, in other words, their CORtinents and seas. For instance, in observing the sun, we discover one of his spots on his eastern limb or edge, and by watching it, find t~at it passes over his disc and disappears from his western limb in about 12 days and 19· hours. From this we infer that it would pass around and reappear "!here it was first seen, in 12 days and 19 hours longer; making the time of the entire revolution 25 days and 14 hours. It is in this way that the time of the revolution of the planets upon their axes is determined. The effect of the rotation of the planets in modifying their forms, will be shown in the next lesson. Lesson. ~~. TRUE FIGURE OF THE PLANETS. The spherical form of the planets evinces the supreme wis!iom of the great Creator. Were they cubes, (or in. stance, instead of spheres,- their temperature would be Car • -, THB BeLInI'" 39 Jess regular than it DOW is; the 8un would rise suddenly upon a whole side at once, and as suddenly disappear at night; and the blessings of twilight, and the gradualsuc. cession of day and night, as they DOW transpire, would be unknown. On the' maps the planE!tS are represented as exactly round, ~r spherical; but this is not their precise form. Their rapid motion around their respective axes has a tendency to depress or flatten them at their poles; and extend or widen them at their equators. Hence their equatorial diameter is considerably greater than their polar diameter; the true figures of the planets being that ()f oblate Bpheroida. The difference between the polar and equatorial diam •. . eter of the planets respectively, so far as known, is as follows: . . Earth, • • 36 miles. Jupiter, • • 6,000 mile•• Mars, • • 25" Saturn,.. 7.500. " Lesson ~3. THB ECLIPTIC. (Map 5.) The Ecliptic is the plane or level of the earth's orbit, indefinitely extended. Fig. 1 represents the earth in her orbit, as she would appear to a beholder placed at a dis. tance, and elevated above the plane of the ecliptic. She is represented in perspective as appearing smaller as shQ grows more distant-as keeping her poles tow~rds the same points in the heavens; and as exhibiting the phases of the moon according as we- see more or less of her en. lightened side. She is colored green, as she \lsually is through the series, to represent ne~ vegetation. The arro.ws placed in har orbit show her direction. If the student has any difficulty in getting a rQrreot idea respecting the ecliptic, let him SUppofie the orbit of th.e earth to be a hoop of small wire laid ~pon a 8Bble: t.he surface of the table, both within and without the hoop, would then represent the plane of the ecliptic. 40 OBLIQUITY OF TBB BCLIPTIC. From the above definition and description, it will be leen that the ecliptic posses through the centre of the earth, and the centre of the sun; conseq uentl y the ecliptic and the appar~nt path of the sun through the heaveDs are in the same plane. It will be ea.sy, therefore, to ascenain the true position of the ecliptic in the heavens; and to imagine its course among the stars on the other lide of the globe. l Lesson ~4:. THE POLES OF THE ECLIPTIO. (Map 6.) , The poles or the earth are the extremities of her axis. The poles of the ecliptic are the extremities of the im.. aginary axis upon which the ecliptic seems to revolve. The ends of a rod or pointer, run through the. map at the centre of the SUD, would exactly represent the poles of the ecliptio. As the ecliptic and equator are not in the same plane, their poles do not coincide, or are not in the lame points in the heaveDS. Lesson ~3. OBLIQUITY OF THB BCLIPTIC. (Map 8.) It has already been stated that the sun as well as the earth is always in the pIllne of the ecliptic. But he is north o( the equator for six months, and south six months. It follows, therefore, that one.. half the ecliptic is south of the plane of the earth's equator, and the other half north of it. As the axi~of the earth is inclined to the ecliptic 23° 28', her equator must make the same angle to the ecliptic in the opposite direction; and the ecliptic must erosa the plane of the equator obliquely. The angle or 230 . THE ZODIAC-SIGNS, BTC • 41 2R' thus made is what constitutes the obliquity of the 8cliptic~ This subject will be better understood by examining the ,figure of the earth, and the position of her equator, as represented on the map. Lesson ~6. TBB ZODIAC. (Map 6.) The Zodiat: is an imaginary belt 160 wide, namely. 80 on each side of the ecliptic; and extending from west to east quite around the heavens. It is represented on the map by the plain circles above and below the ecliptic. In the heavens the Zodiac includes the sun's apparent path, and a space of eight degrees south and eight degrees north of it. Lesson ~7. SIGNS OP THE ZODIA.C. (Map 5.) The great circle of the Zodiac is divided into twelve equal parts called 8igna. These divisions are shown on the map by the spaces between the perpendicular lines that cross the Zodiac. The ancients imagined the stars of each sign to represent sbme animal or object, and gave them names acoordingly. . The names, order, and symbols of the twelve signa of the Zodiac, are as follows: Ariel, or the Ram, • TatU'U8, the Bull, • Gemini, the Twinl,. Cancer, tbe Crab, • Leo, the [Aon, • • Virgo, the Virgin, • ." Libra, the Balance, '. • ~ • II •§ • ~ • 1tR ,. .6 Scorpio, the Scorpion, • 111. Sagittarius, the Archer, t Capricomus, the Goat, • ~ Aquarius. the Waterman, Pisces, the Fishea, • • = * The anoient Astrologists supposed that each of the81 42 NODES-A.SCBNDING AND DESCENDING. signs governed some partioular part of the human body; and even in modern times people sometimes consult the frontispiece of their almanacs, to see whether the" sign" is "in the head," or "in the heart;" 80 as to attend to certain important atr~irs "when the sign is right." The idea seems to be that the word "aign" signifies an omen or prognostication; and that the signs of the Zodiac have some mysterious control o,·er the destiny of man. But this fragment of heathen ~trology is fast falhng into disrepute; and it is hoped will sooo be utterly banished from every civilized country. Lesson ~S. NODES-A.SCENDING AND DBSCENDING. ~: (Map 5.) "a" II ~". .:~ I Fig. 1 represents an interior planet as revolving':~D an orbit inclined to the ecliptic at an angle of about 4~ ; and as both planets revol ve around the same centre of at. traction, the interior planet must pasl:I through the plane of the ecliptic twice at every revol ution: once in ascend. ing, and once in descending. These two points, where the orbit of a planet passes through or cuts the plane of the ecliptic, are called the node. of its orbit. One is called the ascending, and the other the descending node. On the map A. N. is the ascending node, and D. N. the descending node. They are also denoted by the follow. ing characters, viz.: g for the ascending, and U for the descending. A line drawn from one node to the other is called the line of the node., and may be seen on the map, marked L. N. . In the figure the ascending node is represented as being in the middle of Libra, and the descending in the middle of Taurus. The design is merely to illustrate the IU bject, without representing the actual line of the DOOea of anyone of the planets. TIlAK81T8. Lesson 43 ~9. T1lA.NSITS. (Map 5.) By consulting Fig. 1 it will be seen that if an interior planet 'vas at her ascending node, and the earth on the line of the nodes, on the same side or the ecli ptic, the planet would seem to pass over the body of the sun, 88 shown in the figure. This passage of a planet over the sun's disc, or between the earth and the SUD, is called a Transit. Mercury and Venus are the only planets that can make a transit visible to US; as all the rest are exterior to the earth's orbit, and consequently can never come betweea the earth and the sun. But the earth. may make transits visible from Mars, the Asteroids, and Jupiter; and they in turn may make transits for the inhabitants of all exte. rior worlds. The principle is, that each interior planet may make transits for all tbose that are exterior. But transits can never occur except when the interior planet and the earth, or planet from which the transit is seen, are both on tbe line of the nodes. The sun and both the planets will then be in a line, and the one near· est the sun will seem to pass, like a dark round spot, over the sun's face. - , . If the orbits of Mercury and Venus lay in the plane of the ecliptic, (see Lesson ~S,) they would make transits ,rhenever they were in conjunction with the sun. Even with their present inclination the same phenomenon would take place twice in every revolution, if Venus and the earth, for instance, were' to start together from the line of Venus's n<?des, and revol ve in the same periodic time. Venus would then al ways make a transit in passing her nodes. To calculate transits at anyone node, we have only to find what number of revolutions of the interior planet are exactly equal to one, or any number of revolutiolll .1 44 TJl.A.NSITS OF M.RCURY. the earth; or in other planet will again meet on In the case of Mercury 865.256; from which we O( 7 periodieal l8YoiutioD8 13" " 33" " 46" " words, when the earth and the the line of the planet's nodes. this ratio is as 87.969 is to ascertain that of the Earth are equal to 29 of Mercury; . " " " 54 u ,. " " 137 II " " " 191 " Therefore transits of Mercury, at the lame node, may happen at intervals C!f 7, 13, 33, 46, &c., years. All transits and eclipses are calculated upon these . princi pIes. Lesson 30. TRANSITS OF MERCURY. (Map 5.) The following is a list of all the transits of Mercury (rom the time the first was observed, Novembe~6, 1631, to the end of the present century. l63l-November 6. 1776-November 2. 1644-November 6. 1782-November 12. 1651-November 2. 1786-May 3. I 789-November 5. 1661-May 3. 1664-November 4. 1799-May 7. 1674-May 6. 1802-November 8. 18IS-November II. I 677-November 7. 1 ~22-November 4. 1690-November 9. 1697-November 2. 1832-May 5. 1707-May 5. 1835-November 7. 171 O-N ovember 6~ 1845-May 8. 1723-November 9. 1848-November 9. 1861-November II. 1736-November 10. I 86S-November. 4:. 1740-November 2. 1743-November 4:. 1878-May 6. l753-May 5. 1881-November 7. 1756-November 6. 1891-May 9. 1769-November 9. 1894-November 10. ftAlfSITS OF VBWI. 46 \ By c are fu}] y examining the foregoing table it will be leen that the transits of Mercury all occur in the months of May and November. The reason for this is, that hi. ascending node is in the 16th degree of Taurus, and bis descending in the 16th degree of Scorpio; the first which points the earth always pa88es in November, and the other in May. All the traosits, therefore, that happen in November, are when Mercury is at his ascending node, and the residue are w,hen he is at his descending node. Again: If we take the transits in their order, as laid down in the table, they will be found not to occur at intervalR of 7, 13, 33, 46, &c. years, as previously stated ; but if we take those only th~t occur at the .arne node, we shall find them regulated according to the ratio prescribed. For example: from 1631 to 164+ is 13 years; from 1644 to 1651 is 7 years; from 1651 to 1664 is 13 yeara; from 1664 to 1677 is 13 years; from 1677 to 1690 is 13 years; from 1690 to 1697 is 7 years, &0. Thus far their intervals are 7 and 13 years; but they may bappen at the other periods. If we take those occurring in May we shall find them conforming to the same ratio; as previously laid down in Lesson 29. or Lesson 31. TRANSITS OF VENUI. (Map 5.) 8 periodical l8yoluticma or the Earth are equal to 13 of Vea. . 135 u " "" "382" 243" " "" "346" '251" .e "" "408" 291" " .." "475" The line of V enus's nodes lies in the middle of Gemini and Sagittarius; which points are passed by the Earth io December and June. It follows, therefore, that transits of Venus must always happen in one or the odler of these months. ~ 46 INCLINA.TION OF THB ORBITS 01' TIIB PLANBTS. I The following is a list of all the transits of Venus (fom 1639 (the time the first was observed) to A.. D. 2012~ 1639-December 4. 1874-December 8. 1761-Juoe 5. 1882-December o. 1769-1 une 3. 2004-J une 7. 1822-December 6. 2012-Juoe o.. Here it will be· noticed, that the transits for December occur at interv.als of 235 and 8 years; and those of June at intervals of 8, 235, and 8 years, according to the ratio previously stated. Lesson 3~. INCLINATION OP THE ORBITS OF THE PLANBTS TO THB PLANE OF THE ECLIPTIC • . (Map 5.) , Fig. 1 represents the orbit of. a planet. as inclined to the ecliptic at an angle of about 45 0 • But none of. the planets ha ve 80 great an inclination; the main object here being to illustrate the subject of nodes. The inclination of the orbits of the several ,planets to the plane of the ecliptic, is shown in Fig. 2. In the centre is seen the sun. The dotted line running hori. zontally across the map, and through the sun~s centre, represents the plane of the ecliptic. On the right and left are seen arcs of a circle, divided off, and numbered every ten degrees. The plain lines, ·inclined more or less, and passing through the centre of the sun, repre. sent the plane of the orbits of the planets respectively. Un the left, outside the graduated circle, are seen the Dames of the planets; and just witJtin the circle the amount of the inclination of their orbits. This inclination is as follows : Mercury. • • • 7 0 Ceres • • • • • 10 0 Venus • • • • 31 Pallas • • • • . 34 Earth •••• Jupiter. • • • • I 2 Mars • • • • • Saturn. • • • • 2 Vesta. • • • • 7 Herschel • • · • 4 Astrma • • • Le Verrier, not determined. Juno • • • • • 18 I · 71 l CBLBSTIAL LATITUDB AND LONGITUDE. 47 The wide colored portion of the graduated circle showl the limits or the Zodiac, extending 80 on each side or the ecliptic. It will be seen that the orbits of most of the planets lie within the limits of the Zodiac; but Juno, Ceres, and Pallas extend beyond its bounds. They are therefore sometimes called the ultra zodiacal planets. The orbit of La Verrier is not inserted in the map. N ear the middle of Fig. 2 are seen two come" in their orbits; one coming down from the heights North or the ecliptic, passing around the sun and then reascending; and the other coming up from the depths South or the ecliptic. The design is to illustrate the fact that the comets do not revolve in the plane of the ecliptic, or as nearly so as do the planets; but that they approach the sun from all directions, or from every point in the heavens. Lesson 33. CBLESTIAL LATITUDB. It will be understood by LessQn 25; that the ecliptic and equinoctial are two different planes,. intercepting each other at an angle or 23,0. Now, although terrestrial latitude is distance north or south of the earth's equator, yet celestial latitude is not reckoned from the celestial equator, or equinoctial, but from the ecliptic. Celestial latitude is, therefore, distance 'I&Orth or Bouth of the ecliptic; and as one half of the ecliptic is ,outh of the earth'8 eq 00· tor, (Lesson 25,) it follows that a star may be in celestial latitude, which is, nevertheless, ,outA of tAB 6lJUl,· nor'" noctial. Lesson 34. CELESTIAL LONGITUDB. (Map 6.) Longitude on the earth is distance east or weat (rom any given point. qn all English charts and globes it i. .11 48 LONGITUDB OP PLANETS' ASCBNDING NODBS. reckoned from Greenwich Observatory, near London; but on those of American origin it is usually reckoned from the meridian of Washington City. Longitude in the heavens is reckoned from the vernal eq uinox, or the first degree of Aries, eastward, around the eclipt'lc to the same point again. The map is a vertical view of the Zodiac, and when suspended to the south or the learner, gives a pretty correct idea of its poHition in the hea veDS. Beginning at the first degree of the sign Aries, and passing eastward around the ecliptic, the longitude is marked off in degrees on the map, and numbered every ten degrees. The entire circle, like all other circles, consist.s of 360 degrees; which bring us to the point from which we started. From what has been said, it will be obvious that if the sign Aries, for instance, were directly overhead, or on the meridian at any given time, Libra would be in the oppos~te part of the Zodiac, or in the heavens beyond the other side of the earth. In using longitude to describe the position of stars or other objects in the Zodiac, we should say the Twins were between the 70th and 80th degrees; the Lion between 130 and 140; the Balance between 190 and 200; the Goat between 280 and 290, &c. The student can traoe them out for himself; and mark their longitude. . Lesson 33. LONGITUDE OP THE ASCENDING NODES OP THE PLANETS. (Maps 5 and 6.) On Map 5, Fig. 1, the line of the nodeR of the interior planet enters the middle of A ries, and the middle of Libra'. It was stated in Lesson ~O, that the ascend. ing node of Mercury was in the middle of Taurus, and his descending node in the middle of Scorpio. This will be fully illustrated by Map 6, where the line of his nodes is shown, aad their longitude marked. The m,p 49 LONGITUDB OF PLAluITS' ASCBNDIXG NODBS. represeots the plane oC the ecliptic, and when placed ID the south side of the schoolroom, corresponds with the position oC the ecliptiQ in the heavens. The north side, or side towards the learuer, is oonsidered as ahove the ecliptic, and the south side below it. To pass the plane of the ecliptio, therefore, from South to North, is to tUcend; and to return from North to South is to de8cend. The arrows Dearest the sun show not only the direction of Mercury t a8 he moves in his orbit, but also his relati ve distance from the SUD, and the position of his nodes in the ecliptic. The entire line of Venus's nodes is also laid down ,on the map, together with her distance from the eUD, and direction, shown by the arrows crossing the line. In astronomical tables, the longitude of the ascending node only is given; for when this is ascertained, that of the descending' node is easily inferred from it. Take for instance, the a~nding node of Mercury: it is laid down OD the map b8 in longitude 46 0 •. Of course, then, hi. descending DOcIe is in thC!ropposite side of the ecliptic, 9f just 1800 distant. Add 180 to 46, and we have~tI26, tii~ actual longitude of his descending node, as showIl by the map. So by adding 180 to 75, the longitude of Venus'.· ascending node, we have 255, the longitude of her descending node. I have therefore given only the longitude of the ascending nodes of the planets, and one half the line of their nodes on the map; leaving the longitude ,lfthe descending nodes to be ascertained. in the manner already explained . . The longitude of the ascending nodes the planets respectively, is as follows: or or Mercury - • - 460 Venus - • - - 75 Earth. - • • Ceres • • • 800 • Pallas - • • • 173 Jupiter. - - 98 Satttm. - • • 112 Herschel - - • 72 Le Verrier-undetermined. Mars • • • - 48 Vesta • • - • 108' Astnea . - • - 120 Juno • " - • 171 This subject JJhould be well . understood before the learner dismisses it, to euter upon the next leuon •. · 5 ' • .00 CORSTBLLATIONS OF THB ZODI&C. Lesson 36. CONSTELLATIONS OF THB ZODIAC. (Map 6.) Bv this time the student is no doubt anxious to know the "meaning of the strange-looking figures that .are placed around this map, in the signs of the Zodiac. It must not be forgotten that a lign is merely the twelfth part of a circle. The largest circle on the map is divided into signs, as well as into degrees. In each sign, and outside of the circle, is placed a picture of some kinda bull, a lion" a lady with wings, a goat, or some other figure. The reason for this we will now explain. Outside the divided circle on tile map, and around the different fieures or pictures, may be seen numerous star,. Some are larger than others, and they seem to be scatJ 1 tered about at random. Such is the natural appearance ~ . of the bea vens generally, in a clear night, as well that . belt stretching over from west to ~ast called the Zodiac, as any other portion. Now the ancients imagined that the stars were thrown together in clusters resembling different objects; and they consequently named the'ifferent groups after the objects which they supposed them'" . to resemble. These clusters, when thus marked out by the figure of some animal, person, or thing, and named accordingly, were called ConatellafiO'll.8. As every part of the Zodiac is filled with stars, each sign has one or more of tbese ancient constellations. It is on this account that the figure, supposed to be represented by the constellation of each sign, is still retained; and the signs bear the names Df their respective constellations. The pupil will now more clearly discover the folly of the idea- that each sign or constellation of the Zodiao "governs" a particular portion of t:le human body, 88 stated in some almanacs.· How preposterous the notioD TBB SUN'S APPABBlfT KOTIOK IX TBB ECLIPTIC. 61 that ~ cluster of stars, millions of miles from our globe, govern a man's head, his arms, or his feet! And yet sdme still think the "signs" should be consulted in refer. ence to many important matters. The names of the signs have already been given in Lesson 27, to which the learner may again tum, to re. fresh his memory, in conneotion with the map now beCore hinGe . Les80n 37. THE SUN'S UPA.RENT MOTION IN T1m ECLIPTIC. (Maps 5 and 6.) In Map 5, Fig. 1, the earth is seen performing hel annual journey around the sun. Now when the earth is in the sign :0: the sun will appear to be in cr; and as the earth moves on to 111., the sun will appear to pass around to ~. Hence, as the earth pass8s around in her orbit every year, from west to east, it is obvious that the "Uft will appear to make the circuit of the heavens in the same time, and in the same direction. . ;.. ',. .. All .the constellations of the Zodiac seem to overtake aDd pass by the sun westward once a year; or in other , words, the sun appears to meet and pass through them all ~astward, in regular order, every 365 days .. Map 6 may ~llustrate this subject still more clearly. The sun is seen in the centre. Around the SUll the earth is seen in her orbit, the arrows showing her direction. Now when the earth is in ~, in November, the SU~ must seem to be in 111, on the opposite side oC the ecliptic. So when the earth is in n, the sun will appear to be in I, &0. On the 20th of March the ear(h, is in longitude 180, or in the first degree of =01; at which time we s'-l the lUn enters cr. . The time of the 8un'. entrance into the different sip is as {ollowa:".... 62 SUCCESSIVE APPBARANCB OF THB CONSTBLLATIONS. cr, ,March September 23d. 111., October 23d. . I, November 22d. ~, December 21st. =, January 20th. February 19th. It must not be forgotten that this motion oC the sun eastward around the Zodiac, is merely apparent; and is caused 'altogether by the revolution of the earth around the SUIl. By following the earth in her orbit from March 20th, around to the same point again, th~ sun will seem to enter all the signs, in the order, and at the times speci'fi~d in the foregoing table. As we have our spring while the sun )8 passing through 'r, ~, and II, these are called the spring signs; ~, bt, and "R, are the 'BUmmer signs; :Or, fIl, and t, are the autumnal signs; and "', =, and the winter signs. This subject will be still further illustrated in the next lesson. 20th. ~, April 20th. II, May 21st. §, June 21st. &\., July 23d. 1lR, August 23d. :0=, . *, *, Lesson 3S. SUCCESSIVE APPEARANCE OF THB CONSTELLATIONS IN TO NOCTURNAL REA VENS. (Map 6.) Weare very apt to suppose that because we see no· Itars in the daytirne, there are none in the heavens above us. This is an erroneous conclusion. Were it not for the light of the ,sun, the stars would shine ou~ as brightly during what we now call. the daytime, as they ever do in the night; but instead of seeing the same constellations that we see in the night, at any given time, we should see those only that were visible in the night 8iz mont"" , before; and would be above the horizon again in the night six months afterwards. The fixed stars surround the solar system in every direction; and the fact that we cannot see the stars beyond the sun, 'or in that half of the Zodiac in which he DISAGRBElIBNT .BBTWEBN THB KONTBS AND SIGNS. 63 appears, (on account of his superior light,) is no proof that suoh stars do Dot exist and shine. W hen the sun is te>tally eclipsed, the stars appear in the daytime; and if we look through a long tube or descend into a deep' well, 80 as to sh ut the strong light of the sun from the eye, the stars may be seen even at noon in the heat of summer. Let this subject be illustrated by the map. Suppose a person to be observing the constellations of the Zodiac on the 21st of June. At midnight all the constellations (rom :01 around to cr would be in sight; but at twelve o'clock the next day, when the other half of the Zodiac would be above the horizon, the sun would be between the observer and the signs II and ~, and would shed 80 strong a light over the whole visible heavens, a8 to eclipse or obscure all the stars. But as the earth passes on in her orbit, and the SUD seems to pass the signs eastward in regular order, the constellations will arise earlier and earlier every night; so that all of them will seem to pass over from east to west in the night. in the course of a year. This map may be used to show what constellation. will be on the meridian at twelve o'clock, or at any other hour of the night, during every tnonth in the year. In December they will be II and $; in March "R and .0.; in June t and ~, &0., as the earth advances eastward in her orbit, and turns from west to east upon her axis • ., . Lesson 39. DISAGB.BBKBNT BETWEEN TilE MONTHS AND SIGNS. (Map 6.) The names of the months are marked around on the map from we.st to east, to show at what time the earth 0ccupies any particular place in her orbit; and also when the sun enters the opposite sign. But the months and the signs do not exactly agree in longitude. The earth reaches long. 1800 , and the sun enters T on the 20th or ~.rch; 80 that ~here are eleven days of March left aftel the earth has passed into =0=, and the SUD baa entered ". 6- THE BQUINOXES. ()f course, then, all the months in the year are a little more tardy, so to speak, thaD the signs; and are rep ra: , lented, in the map, as jutting by them eastward about ten degrees of longitude. Lesson 40. THE EQUINOXES. (Map 6.) The great circle of the Zodiac is divided into four parts, by imaginary lines running through the centre of the sun, and at riCht angles with each other. On the map they are dottet4. to distinguish them from others, one running perpendicularly, and the other horizontally. The .. earth is represented as being at the points where these lines cross her orbit. Two of the,e points, namely, the upper and lower, are called the equinoctial points. They are so called because when the earth is at either of them the sun shines perpendicularly on the equ~tor, and consequently to each pole; and the day. and nightfl are of equallengtA all over the world. The plane of the equinoctial passes through the earth'. equator; or, in other words, it is the equator of the earth " extending off into the heavens in every direction. • The earth passes the equinoctial points on the 20th of March and the 23d of September; the first of which is called the 'Vemal, and the latter the "u'umfUll equinox. These points being in opposite portions of the heavens, are, of course, 1800 apart, as appears by the map. Lesson 41. 'PRECESSION OF TH~ EQUINOXES. The best explanation of this nice and intricate motion with which we have ever met, is from the pen of the PUCESSION OP THE BQ11UfODS. lalb~nted 55 Burritt; and &8 we have DO wiah to affect originality at the expense of utility, we inae~ the follow. ing extract for the perusal of the student. It is taken (rom a chapter on the subject in the cc Geography of th(, Heavens." " Of all the motions which are going forward in the Solar System, there is none, which it is important to notice, more difficult to comprehend, or to explain, than the PRECESSION OF THE BQUINOXES,' a8 it is termed. "The equinoxes, as we have learned, are the two opposite points in the earth's orbit, where it crosses the equator. The first is in Aries; the other, in Libra. By the preee88ion of the equinoxes is meant, that the intersection of the equator with the ecliptic i. not always in the same point :-in other words, that the .~un, in its apparent annual course, does not cross the equinoctial, spring and autumn, exaotly in the- same points, but every year a little behind those of the preceding year. "This annual falling back of the equinoctial points, il called by astrooo01er8, with reference to the motion of the beavens, the Prece,sion of the Equino:re8; but it would better accord with fact as well as the apprehension of the leamer, to call it, as it is, the Rece8aionof the Equinoxes: for the equinoctial points do actually recede upon the · ecliptic, at the rate of about 5ot" of a degree eve.ry year. It is the name only, and not the position, of the equinoxes .-:hich remains permanent; Wherever the sun crosser the equinoctial in the spring, there is the vernal equinox and wherever he crosses it in the autumn, there is the au tumnal equinox; and these points are constantly moving to the west. "The sun revolves from ODf' equinox to the same equinox again, in 865d. 6h. 48' 47/ .81. This constitutes the natural, or tropical year, because, in this period, ODe revolution of the seasons is exactly completed. But it ii, meanwhile, tQ be borne in mind, that the equinox itself, during this period, has not kept its position a(llong the stars, but has deserted its place, and fallen back a little to meet the sun; whereby the sun has arrived at the eq niDOI: before he has arrived at the same position among 56 THE t;OLSTICBS. the stars from which he departed the year before; and consequently, must perform as much more than barely a tropical revolution, to reach that point agaiJl. "To pass over this interval, which completu the BUft'. 8idereal revolution, takes (201' 221'1'.94) about 22 minutes and 23 seconds longer. By adding 22 minutes and 23 seconds to the time of a tropical revolution, we obtain 365d. 6h. 91n. 10:8. for the length of. si,clereal retJoluticm; or the time in which the sun revolves from one fixed star to the same star again. "As the sun describes the whole ecliptic, or 3600, ir a tropical year, he moves over 59' 811'1' of a degree every day, at a mean rate, which is equal to 5011'1' of a degree in 20 minutes and 23 8~conds of time; consequently he will arrive at the sam~ equinox or solstice when he is 50!" of a degree sl~ort of the 8ame star or fixed point in the heavens, from which he set out the year before. So that, with resper,( to the fixed stars, the sun aod equinoc• tial points faU back, as it were, lOin 7Ii years. This will make the stats appear to have gone forward 10 , with respect to the 8igna in the ecliptic, in that time: for it must be observed, that the 8ame. aigna alway, keep in tIuJ Bame points of the ecliptic, without regard to the place of the cDnltellati0ft8. Hence it becom~s necessary to have new plates engraved for celestial globes and maps, at least once in fifty years, in order to exhibit truly the al. tered position of the stars. A t the present rat.e of motioa.. the recesaion of the equinoxes, as it should be called, or the prece88icm of the stars, amounts to 300 , or one whole sign, in 2140 years." Lesson 4~. THE SOLSTICES. (Map 6.) The dotted line running horizontally across the map is the lloe of the solstices; and the points where this line crosses the earth's orbit are called the 80utitial poi,,". 57 TBB COLl1JlBS. At the time of tb~ autumnal equinox, Septemoor 23d, the sun is directly over the earth's equator, and his light extends to both poles, as shown on the map. From thi. time to December 21st, the SUD declines south, till it is perpendi~ular over the tropic of Capricorn, (so called (rom the sign which the sun enters on that day,) woeD its Southern declination is stayed or ce~s. Hence the Dame solstice. From December 21'" to March 20th the lun approaches the equinox, which it reaches at the latter period, when h8 begins to decline northward, till on the 21st of June he reachetf the tropic of CaRcer. He is then at the 6U1n.mer solstice. From June 21st to September 28d the sun agairY."fipproacbes the equator or equinox, at which time he begins again to decl ine south, &0. This declination of the sun north and south, and hi& apparent passage through ~he plane the equinoctial, . twice a year, are caused by the inclination of the axis of the earth to the plane of the ecliptic, and her revolution around the SUD. What we have here said will serve more fully to illustrate Lesson 25, where the obliquity. of the ecliptic is considered. or Lesson 43. THE COLURES. ... (Map 6.) The Colurel are two great circles crossing at the pole• .'!I the ecliptic, (see Lesson 24,) and passing through the . ecliptic at right angles. One passes througb the equinoxes, and is thence caned the Equinoctial Colure; the other passes through the solstices, and is called the Solsti. tial Colure. They are to the heavens what four meridi. ana, each 900 apart, would be to the earth. They divide the celestial sphere into four parts, like quartering an apple. Two hoops of wire, crossing between the eye of the student and the sun, and also directly beyond the sun on the other side of the map, would represent the colures; , 58 PBRIHELION ANIJ APBBLION. provided one paased through the map at the solstitial, and the other at the equinoctial points. When once the place of the colures is clearly ascertained, they are very COD. venient in finding particular stars or constellations either north· or south of the ecliptic. ' Lesson 44. ELLIPTICITY OP THE P!NETS' ORBITS. (Map 7'.) .. • 1 i • i I Thus far we have proceeded upon !Ie supposition that the orbits of the planets were exact circ~s, and that CODsequently the several planets were· al waj't at the 8am~ distance from the 8U~ I t is time DOW to state more definitely tb.~ true figure of their orbits. Fig. 1 represents the earth as revol ving in an ellip8e, or cmal-a.Aaped orbit. This is its true figure; and indeed, to a g,e~t extent, the figure of all the .planetary orbits. But some ·~re more elliptioal than others, and the orbits' of the comets, ~,shown in Maps 2 and 5, are more elliptical than thos8 ..of.'~~y of the planets. Not only. are 1fle', orbits of the planets elliptical, but the sun is always found one side of the centre, or Dearer one. end of the ellipse than the other, as shown on the map. The point where the sun is placed is called one of the foci of the ellipse. ~ Lesson 43. PBIlIBBLION AND APRELlqN. (Map 7.) . Wilen a planet or comet is in that part of its orbit near. est to the SUD, it is said to be at its perihelion; and wilen at the point most distant, at its aplaelitm. So of the mOOD ; perigee and apogee are the points of her orbit nearest to and most distant Crom the earth. On the map the earth is seen at her perihelion on the left, and at her aphelion on the right, the two points being / • ... I ' ,\' I i I .1 59 BCCENTRICITY OF THE PLANETS' ClllBITS. at very unequal distances from the sun. In stating the distances of the solar bodies, we sometimes give their pee rihelion and apheliOfl, as well as their mean or average distances; but in Lesson 8 the mean distances only are given. The following table will exhibit the longitude oC their periheliMls, respectively: Mercury. .Venus • • • • • • .lar~h Mars Vesta Astrrea • • • • JUDO • • • Ceres Pallas • Jupiter • Saturn • Herschel. La Verrier • • • ••• • • • • • • • • • • 74 0 128 99 332 249 21' 43 46" 31 4 53 5 30 23 .. 56 33,"' 24 27 54 83 46 • • • • • • 147 • • • • • 121 11 7 7' 8 89 9 167 31 299 11 "• • • 135 • 53 • • 85 30 16 00 Lesson 46. ECCENTRICITY OF THE PLANETS' ORBITS. (Map ... ) The ecce'f&tricity of a planet's orbit is the tli8tance of it. U!.~ the centre of the aun. This will be easily UD· ders· observing Fig. 1, where the sun is seen in the left-han cus of the ellipse, and upon the large maps, about two inches from its centre. These two inches would, in this case, constitute the , ecoentricity of the ellipse. The ecoentrioity of the orbits or the different planets, . is as follows: Mercury 7,000,000 miles. • • • Venus • 492,000 " • • • Earth 1,618,000 " • • • • Mars • • 13,500,000 " • • Vesta • • • 21,000,000 • " 62 RIGHT ASCENSION. Fig .. 2 shows the position of the sun at the time of the equinoxes and solstices; the manner in which his light strikes the earth at these times; the :one, of the earth; the extent of the sun's declination, &0. Fig. 3 is still more full and explicit. In addition to what is contained in Fig. 2, it shows the place or decli. nation of the sun for every month in the year, and the manner in which his beanis strike the middle of both the temperate zones during every successive month. Take. for instance, the north temperate zone, at the 45th degree of latitude. On the 21st of December, when the sun has the greatest southern declination, and, as shown in Fig. 2, shines vertically on the tropic of Capricorn, he would seem to be quite low down in the south, even at noon; and his rays would strike the north temperate zone quite obliquely, as shown in the figures. From December 21st to June 21st the sun advance. to*aros the north, and the obliquity of his rays constantly diminishes. On the 21st of June the light falls quite obliquely on the southern hemisphere, where it is then winter. The two lines running off from the earth's surface to the 1ettet Z, . are designed to show the perpendicular and zenith of the 45th degree of latitude; and also how much the sun lacks of being direotly overhead at these points, at the time of the solstioes. I t will be easy to see from these figures that declination 18 to the heave",,' ",kat latitude it to the earth. They may De used, also, to show the use of a quadrant, a~ the manner of determining latitude by the sun'~ .-. Idian altitude, and his declination. Lesson 49. BIGHT ASCBNSION. (Map 6.) Rig'lat A,cenrion is distance east of the vemal equinox, measured on the equinoctial. In Lessons 33 and 34, it was shown that celestial lau. ,.. 63 INCLINATION OF AUS TO OB.BITS. tude and longitude answered to terrestrial, exoept that in the Cormeroase we reckoned from ~nd on the ecliptic, in. stead of the equinoctial. . On the other hand, declination and right asoension re. fer directly to the equinoctial; and consequently ans\ver .to"longitude and latitude on the ~arth. The learner may here start the inquiry, Why were not declination and right ascension oalled celestial latitude and longitude, seeing that they refer to the celestial equa. tor, instead of measurements from and on the ecliptic 1 Such Ii question is not easily answered. This interchange of terms, as it may be called, is rather unfavorable to a ready and clear understanding of these topics. Even at this late period it might be a service to the science in the end, to call declination oelestial latitud~, and right ascension celestial longitude. . Right ascension is reckoned around on the equinoctial to 360°, answering to 3600 or celestial longitude, only that one is reckoned on the equ.inoctial, and the other on the ecliptic. l. Lesson 30. INCLINA.TION OF THB AXES OF THE PLAKET8 PLANB OF THEIR RESPECTIVB OB.BITS. • TO TBB , (Map S.) T~ pupil may fully understand this lesson, it may . be ~~ii ;lecapitulate some things already learned . 1st. The Ecliptic is described Lesson 23. . 2d. The Orbil8' of the planets are described Lessons 4, 43, and 45. 3d. The inclination of the orbita to the plane 9f the ecliptic is the subject of Lesson 32. We now call attention to the inclination of the ozu or the several planets to the plane of their orbits. This is a lesson of great interest and importance; and although so far as the earth is concerned it has already been anticipated, in our remarks on the seasons, d~clina- 64 INCLINATION OP AXES TO .aBITS. non, &c., still it opens a rich field of inquiry before the Itudent, and should receive a good degree of attention. On the map the dotted horizontal lines represent por. tions of the orbits of the planets, with the exception of the sun, in which case they represent the plane of the ecliptic. The azis of each planet is seen inclined to the plane of its orbit at its true angle. The equators are shown by the dou ble lines crossing the axes at right angles. The zonu are distinguished by curved boundary lines, and by the different colors--the torrid zones being red, the temperate green, and the frigid white. It will readily be seen that the extent of the torrid zone of a· planet depends altogether upon the amount of its polar inclination. If its axis be much inclined, as in the case of Venus, it will have a wide torrid zone; but if its axis is but little inclined, like that of Jupiter, it will have a narrow torrid zone. The sun's declination north and south of the equator of each planet must be just equal to its polar inclination '; and as its torrid zone includes both its northern and southern declination, it follows that .it must be twice as wide as the alDount of its polar inolination. These prinoiples will be more olearly seen by the fol. lowing table, in which the polar inolination, greatest de. clination, and width of torrid zone, are oompared : Inc. of axia. Declination. ;:0,00' Torrid zon•. Venus • • • 75 0 O<Y 75° 00' 66 Earth • • • 23 28 23 28 Mars • • • 28 40 28 4:0 57 20 Jupiter • • • 8 5 8 5 6 10 Saturn • • • 80 00 30 00 60 00 The SUD • • 7 20 Only the first part of this table nee~ be committed to memory; but the whole should be studied and compared with the map until its principles are fully understood. or Mercury, the Asteroids, Hersohel, and Le Verrier, nothing definite is known respeoting their polar inolina. tion; oonsequently we have no knowledge of the extent of their zones, or the charaoter of their seasons. 66 Lesson 31. SEASONS OF THE DIFFEB.ENT PLANBTI. (Map S.) The general philosophy of the seasons, together with the seasons of the earth, are already explained in LessoD 46. The same subject will now be resumed, as it relatel to the rest ot the pI anets. The seasons of the planets depend upop two causes: the inclination of their axes to their respective orbits, and their periodic revolutions around the 8un. The former determines the eztent of their JOne8, and the latter the length of their 8etUOM. The effects df polar inclination are seen in the contrast presented by Venus and Jupiter. Venus, with a polar inclination of 75°, has a torrid zone 15()O wide; while Jupiter, whose axis is inclined but 3° 5', has a torrid zone only 6 0 10' wide. After the statement, of these general principles, w.e shall proceed briefty to notice the seasons of the several planets. It might be well, however, for the student to turn back to Lesson 46, and review it in connection with this map. Especially let him examine the figure of the earth and her zones with a view to the obliquity of the ecliptic, explained in Lesson 25. Call to mind al80 the subject the..aun's declination, Lesson 47, and the difference be. tween r~rring to the ecliptic, as in celestial latitude and longitude, and to the equif&Octial,8s in right ascension and deolination. See Lessons 83, 34, 4:7, and 4.8. or Lesson 3t1. SEASONS OF VENl7S. (Map S.) The tropics of Venus are 75 0 from her equator, ~d within 150 of her poles. She has no frigid zone, or polar. 6* , 66 SBA.SONS OF !IIA.RS. circles. Her periodio time being only 225 days, (Lesson 18,) the sun passes in that'short time from her northern solstice through her equinox to her southern solstice, and back to the point from which he started. So great is the sun's dec1i9ation on Venus, that when he is over one of her tropics, it is winter not only at the other tropic, but also at her equator; and as the sun passes over from tropic to tropic, and back a,gain every 225 days, making spring at the equator as he approaches it, summer as he passes over it, autumn as he declines from it, and winter when he reaohes the tropic; it follows that at her equator Ven us has eight ,ea,01I8 in one of her years; or in 225 ol our days. Her seasons, therefore, at her equator, consist of only about four weeks of our time, or 28} days; and from the heat of summer to the cold of winter can be only about 56 days. At her tropics she has only four seasons or 56 days each. A t first view it might appear to the reader that such an arrangement must be fatal to all vegetable life, especially at Venus's equaior; but it should be remembered that He who inclined the axis of Venus to her orbit, and pre8Cr~bed her periodic time, could as easily clothe her with vegetation of a month's growth, as with that requiring the lifetime of the oak or the cypress to bring it to ~Tfection. Lesson 33. SEASONS OF MARS. • (Map S.) The polar inolination and zones or Mars are very similar to those of the earth; but owing to the difference of his periodic time, his seasons are very different from ours. His year of 687 days is divided ~nto four seasons of about 172 days each, or nearly twice the length of the seasons oC the earth. Hjs 'polar inclination is 50 12' greater than that of the earth; making his torrid zone wider, and his polar oircles greater than ours; while his temperate zones are IOmewhat narrower • • • .'SOKI OP JUPITBll. 67 Lesson 34. 8BA80N8 OP 11JPITBll. (Map 8.) 80 slight is the inclination oC J upiter'a axil to hi, orbit, that it affords him but a very narrow torrid zone. The inclination of his orbit to the ecliptic is but 10 16', and his axis is inclined to his orbit but 3 0 5'; 80 that his axis is nearly perpendicular to the ecliptic. The BUD never departs more than 30 6.1 from his equator, and still, as his periodic time is about 12 years, (Lesson 18,) he has alternately six years of northern and six of southem declination. His narrow torrid zone and small polar circles leave very extensive temperate zones. In paaaing from his equator to his poles, we meet every variety of climate, from the wannest to the coldest, with but slight variatioDs in any latitude, from age to age. His days and nights are always nearly of the same length, as the sun is always near his equinoctial. His poles have, alternately, six years day and six years night. In connection with the above facts, it may be well to 8880Ciate the amount of lWht received by this planet; bie rnagnitu.d,e; his oblate frRure; his rapid roto.tion upon hie axis; and his distance from the sun. The student can. Dot too often call up the facts already learned, as he ad. vances from lesson to lesson. In this way he will 8000 be able to.state the most interesting particulars r~peotiDg each of ilie solar bodies. Lesson 33. SBA.SONS OP SATUllN. (Map 8.) The polar inclination and zones of Saturn differ but liUle frorn those oC Mars; but his seasoDs are greatly modified by the length of his periodic time. This being about 30 years, his four seasons must eaoh be about 7i 68 years 1000g; and his polar regions must have, alternately, 15 years day, and 15 years night. The Rings of Saturn which lie in the plane of his equator, and revolve every' hours, are crossed by the sun when he crosses the equinoctial of the planet. During the southern declination of the sun, which lasts fifteen years, the 80uth side of the rings is enlightened, and haa ita summer. It has al~ its day and, night, by revol ving in a portion of the planet's shadow. When the sun is at tbe southern tropic, it is midsummer OD the south side of the rings; as tbe rays of light then fall most directly upon them. As the SUD approaches the equator, the t~perature decreases, till h~ crosses the equinoctial, and the long winter of fifteeD years begins. At the same time the north side the riDgs begins to have its spring; summer ensues, and in turn it has fifteen years of light and heat. The Rings of Saturn will be turned directly towards the earth, about the middle of September, 1849; at which time the light of the '8un wijl extend to both pole. of the planet. Of course Saturn is then at one of his equinoze,. Seven and a half years after, he will reach one of his 8OLmcu-his rings, as seen, will appear fully expanded from the earth,-the sun will have his greatest possible declination from Saturn's equinoctial, and it will be wi~ter at one of his poleSt and summer at the other. In seven and a half yean longer, he will reach his other equinoctial point, and his rings will be invisible again. Saturn's Rings will be invisible from the 22p of April, 1848, until January 19th, 1849; excepting that they may be aeen from the 3d to the 12th of September, 1848. or the I8880DS of Saturn, and the structu~, dimen. sions, and uaes of his won~erful rings, we shall remark rurther hereafter in a distinct lesson, in connection with Map 11. From Map 8 and the rOTegoing remarks, it must be obvious to the leamer that cold and heat, winter and Bum. mer, "seed-time and harvest," are not peculiar to our globe, but are characteristio every world with which' we are to any oonaiderable extent acquainled. lot or or .. 1 I Lesson 36. CONJUNCTIONS AJf~ OPPOSITION OF PLANBTS. (Map 9.) • " When any two or more of the solar bodies are found ill tJ&e 8ame longitUiU, they are said to be in conjuflCtitm. Fig. 1 represents the Sun in the centre, and Venus, the Earth, and Mars, at different points in their orbits. Ie the Earth was at D, and Venus at I or S, she would be in conjunction with the SUD, both appearing to be at a point between ~ aod II, or according to Map 0, in the 60th degree of longitude. The interior planets have two conjunctions; the anfe. rior conjunction, when between the earth and the SUD, as at I ;. and the 81¥p6rior conjunction, when beyond the SUD, as at S. At the superior conjunction the enlightened side of the planet is towards the earth; and at her infe. of rior, the dark side. When at her superior conjunction, Venos is 154 mil. lions of miles Crom the earth, but when at her inferior conjunction, she is only 26 millions of miles distant. The reason for this great difference will be seen by a glance at the map; whicb shows ber the whole diameter of her ol"bit farther off when at S than at I. . The uterior planets have a n.perior conjunction, as Mars at N; but they can never get between the earth and the sun to form an inferior conjunction. When, therefore, \fa planet gets in the same longitude al the earth, like Mars at F, it is said to be in 0pp08ition • A planet in conjunction rises and sets nearly with the Bun; but one in opposition rises when he 8ets, and seta when he rises. . The position of planets with respect to each other is sometimes represented by an astronomical sign. Thus d denotes conjunction, and 8 qppo8ition~ LeasOn 32 shows the orbit of Venus to be inclined to that of the earth at an angle of 3jP; hence as one half of her o.rbit is above the ecliptic, and the othel half below, 70 BIDEBBAL £1(D SYl'fODIC UVOLnIORS. ahe will always appear either above or below the sun when in .conjunction, except when she is at one of her nodes; in which case she will appear to pass over the sun's disc, as represented in the figure. See Lesson 81. Lesson 37. SIDBREAL AND SYNODIC RBVOLUTIONS. (Map 9.) The 8idereal or periodic re1)olution of a planet is its passage from any particular point in its orbit, around to the same point again. A ,ynodic re-oolutUm is one extending from either an inferior or superior conjunction to the same conjunction again. It is therefore considerably more than one com. plete revol UtioD around tbe sun .. For example: were the earth stationary at D, the su. perior conjunction of Venus would happen 112j- days af. ter her inferior conjunction; or in just half ber periodic time; but as both are in motion in the same direction, one revolving in 365 days, and the other in 225, it is obvious that when Venus reacbes the point I, the earth will be (ar behind; and when the earth reaches D, Venus will have advanced to M in her second round; and will then have to overtake the earth before an inferior conjunction can be effected. This will occur when the earth reaches the point L in her second rou~d. From one inferior conjunction to another is t94 days; requ~ring about 2f revolutions of Venus, and nearly If revol utioDs of the earth. . The periodic times of the planets were given in LeaIOn 18; but for the sake of a better understanding of the subject, the sidereal and synodic periods will here be . given in connection. They are as follows: Sidereal. Mercury Venus • Earth • • - 88 days.. • 225" • • 865" • Synodic. 115 days. 594 " 866 " IIDBUAL AND 8YJlODIC DV'OLVTlOKI. 8ldereal. I .)'Bodic. Mars • 1 year-322 days. • 780 days. Vesta • • 8" 230" • 608 " .. 4" 105 " 476 " Astrma JUDO. • 4" 131" 474 " Ceres • 4" 222" • 466 " Panas • .." 222" • 466 " Jupiter • 11" 317" • 399" Saturn • 29" 175" 378 " Herschel 84" -" 3691 " Le Verrier • 217" 119" • 366t" This is an interesting table, and may be studied for . some time by the more advanced student to great advantage. He may imagine Mercury hurrying round to his . starting-point in 88 days, and in 27 more overtaking the earth, even before she has performed one-third of her an. nual journey. The periodic time or Mars being nearly double that or the earth, his synodic period is but little over two years. By subtracting the earth's period from the synodic period of the rest of the planets, the remainder will show how long the earth is in overtaking the exterior planets re. spectively, after she has completed one revolution. Thus, the synodic time of VeMa is 503 days. In 365 days the earth completes one revolution, and reaches the point from which she set out. Vesta is then 365 days ahead of the earth, but moving at a four years' pace; 80 that in 138 days the earth overtakes her, and they are again in COD. junction. In the case of Jupiter, Saturn, &c., it requires stift less time. Their periods are long, and they move slowly in longitude;. so that when the earth haa completed a period, they are but a short distance in ad. vance, or to the east of her, and she lOOn overtakes them. By subtracting, it will be seen that the time required is, for Jupiter, 34 days; for Saturn, 13 days; Cor Hersohel, days; and (or La Velrier only If days. . Map 2 mIght be serviceable in illustrating this subject, 80 far .a relates to the exterior planets • The learner must Dot forget tbafAlle exterior planets have but one conjuDction, while the illterior have two; q • 71 72 WHEN PLAKBTI AU SAm TO .B STA.TIONARY. and that in the preceding table the time is given from one conjunction to another of tAe Idnd. The opposite OOIlj unction occurs in just half the synodic period. ,a,., Lesson 38. BLONGATIONS OF A PLAN.'!'. (Map 9.) . The elongation of an interior planet is ita angular distance east or west of the sun, according as it follo~s or precedes him. The greatest elongation of Venus is 480 , and that of Mercury only 290. But these alternate elongations east and west are not always the same. Those of Mercury yary from 160 12' to 280 48'; while those of Venus vary much lesS. E and W, on the map, mark the positions of Venus at the time of her greatest elongation. From the above facts several other important conclusions are deduc~d. The first is, that the orbits of Mercury and Venus are within that of the earth. If it were not 80~ they would depart farther from the 8UD, and sometimes appear in opposition to t.hat luoVnary. In the second place, they show that the orbit of Mercury is within that of Venus; otherwise his elongation would equal or exoeed that of Venus. Thirdly, they show the ellipticity of the «;>rbits of Mercury and Venus. If their orbits were oomplete circles, their greatest elongation would alway. be the same; but as it varies, it proves that t..y are Dot always at the same actual .distance from the sun, or, in other words, that their orbits are more or less elliptioal. Lesson 39. WBBK PLANETS ARB SAID TO BB STATIONARY. (Map 9.) For a short time, while at or Dear their greatest eloDlation, the interior planets Beem neither to recede from. l I DI1lBCT ..AND RBTllOGUDB MOTION8. 73 nor approaoh towards, the SUD. They are then said to be dati.ontIry. These periods &re just before and just after an inferior conj uDction. They are represented in Fig. 1 at E and W. At E the planet would be coming touJartll the earth, and at W gai"IJ from it. Lesson 60. DIRECT ..AND RBTROGRADB MOTIONS. (Map 9.) It was stated in Lesson 18, that the planets revolved in their orbits from west to east, or in the order of the signs. But they do not always appear io maintain this order. At times they advance regularly through the signs, and again retrace their course. Hence the distinction of direct and retrograde motions. Direct motion is from west to east; retrograde from east to west. The general course of the planets is eastward, their retrogtession being but for a short time, when the direot course is again resumed. The cause of this seeming irregularity will appear by again consulting Fig. 1. The signs will be seen marked ", ~, II, &c., on the right and left sides of tbe map, and may be imagined around the whole figure. When Venus is at W, she would seem, to an observer on the earth, to be in in the signs of the upper figure. As she passed OD in the direction of the arrows, from W to E, her motion would be ttlirect~ -and she would seem to pass through ", ~, II, §, and into bl; but in passing from E to W she would seem to fall back through ~, II, &0. These are her direct and retrograde motions. But the amount of apparent retrogression is greatly reduced by the motion of the earth in the same direction; 88 for instance, if the earth advances only from D to the lower ~and (o:T) during a revolution o(Venus, she would not retrograde beyond the beginning of~. The above priooiplea are as applicable to Mercury u to Veoua. is *, 74 RftaOO• .ADB .OTJO.8 OP Brrs.loa PUKBTL Lesson 61. UTJ10GUDB MOTIONS OP TBB BITEBIOR PLAlfETS. (Hap 9.) The apparent retrogression of the exterior planets is dected in a manner somewhat difFereDt from that of the interior planets. 8dl'poate the earth at A, and Mars at B; he would be leen BltlO&g the stars at C. As the earth gains upon Mars, and fed.ches the point D, Mars, being at F, would be seen at G, 01" west of where be was first seeD. When the earth reaches H, and Mars is only at J, be will be seeD at K; or ItOme 150 back, or west, of his first apparent position. . The part of the great circle of the heavens through which a planet see~ns to retrograde, is called its arc Of retrogradati.on. In the figure it is the arc of the circle betlveen C and K. The following table will show the arc of retrograde motion, and also tl1e time of retrogression in days:Arc. - Day.. 23. Mercury ISlo Venus 16 42 Earth 16 Mars 78 13 83 Vesta • 12 99 Astrma • 12 Juno .D9 • 99 Ceres 12 • 12 99 Pallas • 10 121 Jupiter • Saturn 139 6 • Herschel • 151 4 • Le Verrier 180 1 • • Here it may be interesting to· observe, that the more distant the exterior planet the less its aTC of ret rograd ation, and the longer its time. The reaSOD for this may be illustrated by the map, Fig. 1. Suppose Mars at F to - - VBNlJI AS EVENING AND ltIORNUfG STAlL. 76 represent Herschel. Now as his year consists of eighty. four of our years, it follows that the earth would pass him eighty-three times during one of his revolutions; and that during a revol ution of the earth he would pus through only {7th part of his orbit; or about Slo. The planet F would thence seem to retrograde slowly on the eel i ptio nearly half the year; or while the earth was passing from A to H on the m a p . . For the same reasons· the arc would be still less, and the time ~f retrogression still longer in the case of La Verrier. The more distant the planet is from the earth'. orbit, the smaller the angle which will be necessary to inel ude that orbit; and the less the arc of retrogradation descril?ed by the planet on the concave of the heavens. Lesson 6~. VENUS AS MORNING AND EVENING STA•• , (Map 9.) .. Next Mercury, Venus runs her larger round, With softer beams and milder glory crown'd ; Friend to mankilld, she glittel'8 from afar, Now the bright efJenin.g, now the morning star. From realms remote she darts ber pleasing ra " Now leading on, now closing up the day; Term'd P hOllphor when her morning beam.. she yiel., And Heq'rus when her ru.y the efJening gilds." It has been seen that in making her revolutions, Venua is sometimes East Bnd sometimes West of the sun. From her infer'or to her superior conjunction she is IDe,t of the sun; and from her superior to her inferior conjunction ea.t of him. N ow it is obvious that when she is west oC the sun she will go down before him, and cannot be seeD in the west after sunset; but if she sets before the SUD she will rise before him, and can be seen in the east be. fore sunrise. When, therefore, Venus is west of the sun. :~f~ she is morning star. When she is east of the sun she·. :t.~' rises aftex the sun, and nlay be seen above the horizorr1n .' . the west, after the sun is set .. She is then e",ening at,ar.·' The .ancients supposed thpse were two different stars, • 76 PlUgS OP oaeny .ARB VBlfVI. calling the fint Ploqluw, and the other.HeqtrU. Venus is alternately one or the other about 292 days. For 146 days after her superior conjunction she lingers Carther and farther behind the sun, in the west, till she reaches her greatest elUtem elongation. Sbe then seems to approach , the sun agaiD for 146 days, w heD she passes her inferior oonjunction, and becomes morning star. After this she rises more and more in advance of tbe sun for 146 days, when, baving reacbed her greatest tDUtem eioDgatioo, she begins to faU back again ~wards the 8UD, and in 148 days is at her superior conjunction. This passed, she i. agai 0 evening sta r. ..' . . Fig. 2 is designed fully to illustrate all that may yet .em obscure to the learner. From W to E w~pre lent her direct motion, in the order of the sign~ ..From E around to W again sbows her retrograde mOtion. S and I mark her superior and inferior conjunctions; and the .appearance of a 'rGuit is represented on the sun's disc. By imagining the sun and Venus as represented in th~ figure, to rise in the east and pass over to the west, the student will see -that if Venul were at W she would he morning star, and at her grFatest elongation; but it at E abe would be evening star, &0. It would be a usefbl exeroise to observe the exact position of V en us in the·, heavens, at the time of studying these le880ns, and then point out that positioD on the map. . LeSSOI 63. PHASES OF IIBRCl1BY AND VElWS. (Map 9.) As Mercury and Venus are opaque bodies, like our earth, only those portioDs of their surface appearing bri~ht whioh are enlightened by the sun; a'nd as their enhghtened sides are tu rned towards U8, little by little, they present, when seen tbrough a telescope, all the cW:. Ce,ent appearanoe8 or phases the moon• or • • TELBSCOPIC VIEWS 0. THE PLANETS. 77 Fig. 2 represents Venus in her orbit, and exhibiting all her different phases, in the course of her revolutioo. At I, her inferior conjuDction, her dark side is towards us, and ber enlightened side invisible. As she pl188e8 from I to' W, and so on round to S, see more and more of her enlightened side, till her whole illuminated disc is in view. From her superior to her inferior COD. junction she continues to wane, till her dark side is again turned directly towards the earth. Although when at S, her whole enlightened hemi. sphere is towards tire earth, still she is le88 brilliant than when at -E and W; owing. to her increased distllnce from us, and her being, apparently, in the neighborhood oftbe sun. It will be seen that Venus is the whole diameter of her orbit nearer to us, at ber inferior conjunction, than at her superior; and as her meaD distance-from the SUD is 69 millions of miles, her distance from the earth must vary to the extent of twice that amQunt, or the whole diameter of her orbit, which is 138 millions of miles. It . is not strange, therefore, that her apparent magnitude undergoes sensible variations between her conjunctioDs. we Lesson 6~. TELESCOPIC VIEWS OF THB PLANBTS. I : • (Map to.) Although in the preceding lessons we have frequently al1uded to th~ appearance of. lOme of the planets, wheD leen. through a telescope, it is thought important to describe those appearances more in detail; and to ill ustrate the descriptions by appropriate engravings.. This is the . object of Map 10. Before any particular planet is noticed, it may be well to state a few general facts respecting these primary bodies. 1. They all have the same general figure, namely, that spheres or spheroids • or .,. 78 TELESCOPIC VIBWI OP TBB PLANETS. 2. They all seem to be surrounded by an atmoqMre, of greater or less density aDd extent. .• 3. The spots or belts seen upon their surfaces (rom lime to time, by different observers, seem to be in the main permllnent, and indicative of large divisions of land and water, like our continents and seas. With these prelimin~ries, tbey will now be taken up aDd considered in order. MERCURY. "Of MBRCURY," says Dr. Herschel, "we can see little more than that it is rouod, and exbibits phases. It is too small, and too much lost in the neighborhood of the 8UD, to allow us to make out more of its character." But this is not the opinion of every obse"er. Mr. Schroeter, an eminent German astronomer, assures us that he haa not only seen 8pOtII on the surface of Mercury, but also 8IOU1&tai1l8, the height of two of which he actually measured. They were situated in the southern hemisphere of the planet, and the highest was found to be Dearly . eleven miles in height. Numbers 1 and 2 on tbe map, are representatioDs or Mercury. The spots supposed to have been seen by Schroeter, are represented on his disc, and he has a faint bluish tint as when seen through a telescope. As else. where stated, he exhibits the different phases of the moon during his synodic journey around the sun. VBNUS. • The figures from 3 to 12 inc) usive, are telescopio views of VenlU. As a whole they represent her various ,la,e,; as already explained in Le880D 63; and il. lustrated by the lower figures of Map 9. Figures 8, 4, 11, and 12, show her horDed, 88 when near ber inferior conjunction. Figures Q and 10 show her as sbe appears wheD at her greatest elongation; 6 aDd 9 as gihbmu, between her greatest elongation and superior conjunction; and 7 and 8 as she appears at her superior conjunction. These ten views present a great varietyJ as it resp6ol11 TELESCOPIC VIBWS OP TUB PLANBTS. 79 or the 'PO" that appear upon the surface the planet. They seem Dot only to vary in form, but al80 in their number. It may be proper, therefore, to state that the. views were not all had by the same penon, Dor during the same period of time. Fig. 8 is a view by ScAroeter, in 1791. Fig. 4: u Bianchini, in 1726. Fig. 5 " Cunni, in 1667. Fig. 6 " " . in 1666. Figures 7 and 8 represent the face of the planet, as it is supposed she would have appeared, at the time of sOme of the other views, had her whole hemisphere been enlightened. It will be seen that each of these figuree combine two other views. Fig. 9 is a view by Schroeter, in 1790. Fig. 10 is a view often bad by the celebrated Dr. Dick. Figures 11 and 12 are repetitions of former views, with the crescent inverted, in order to illustrate the subject of V en us's phases. The wrface ot Venul is variegated with moufttaiu, some of which are estimated to be over twenty miles in height. Three elevations have been estimated at 101, Ill, and 19 miles, respectively. The atmoqMre of Venus is supposed to surround her to tbe depth of only about three miles; but it is 8upposed to be very deus. The color of Venus is a a/very ",hite. When at her greatest .ongation, she is sufficiently bright to cause a perceptible shadow if her light is intercepted . .• THB BARTH. That the leamer may know the grounds of the inferences drawn from the telesC9pic lippea.rances oftbe planets, in regard to their geography, or their great natural divisions, as continents, seas,· &c., we present him at No. 13 with a tele,copic view of tke Earth. Let him imagine himself placed upon Merr,ury, for instance, with a good telescope, observing our planet. At the time of 80 TELBSCOPIC VIBWS OP. THE PLA.NBTS. her opposition she would appear/wI from Mercury. The continents and islands would appear brighter than the rest of her disc; as they would reflect a stronger light than oceans, seas, and lakes. By watching these spots they would be found to cross the earth's disc in 12 hours, from which the observer would infer. that our globe re. volved on her axis in 24 hours; and from the direction of the spots he would deduce the inclinatioa of her axis to the plane of her orbit. From the passage of cloud8 over her 8U rface, and other phenomena, it would be inferred that tbe earth had an atmosphere, and the different zones, and the changes of tbe seasons, might present a variety of COltw8 to the celes. tial observer~ To a person on one of the ezterior planets, the earth would present all the phases of the moon. The study of geography has no doubt made the learner familiar with the figures of the continents, islands, &0., upon the earth's surface; but if he can divest himself for a moment of all particular knowledge of our globe, and contemplate her from a distance, as a planet, with w hat Dew and surprising interest does it invest her! She not only becomes one of a class, from which we may reason analogically respecting the physical constitutions aod design of other worlds; but while we look with wonder upon the planetary orbs, and long to know more of their physical structure, we look upon the earth as the only orb which IDe are allowed to visit, and with whose history ao<Oj pecu. liarities we may now become acquainted. ~jd as the student surveys the whole Western hemisphere, let him inquire, " What iR man /" What is a city. an t:mpire, or a tDOrld, in the great universe of the Almighty' IIA.B.S. ThA figures from 14 to 23 inclusive are representations Mara. The first two, namely 14 and 15, are views by Cassini, 8S long ago as 1610. They are copied from a volume of the Transactions of the Royal Society of Lon. don. Figures 16 and 17 represent views had by Maraldi, a celebrated French astronomer, in 1704. Figures 18 or • TBLBSOOPIC VIBWI OF TIlE .L.A.KBTS. 81 and 19 represent the appearanoe oC the spots on Mara, as eeen by Dr. Hook in 1666, from a drawing made at the time by him. Figures 20 and 21 represent views by Sir William Herschel, previous to 1784. Fig. 22 is a view by Sir J oho Herschel, as copied by Nichol in his" Solar System," and by several other astronomical writers. Fig. 23 is' a view by Dr. Dick, iD 1832, aDd alllO in 1837. It is Jopied, as several of the above are, from his "CelMtial Scenery." . It may seem impossible to the learner that all thj, yariety in appearance could be produced by permanent objects on the su rface of the planets; but let him remem. ber that the map of Mars, which he is studying, is drawn upon a sphere; and that the revolutions of a planet would necessarily produce a constant change, not only in the general appearance, but a1110 in the apparent form of the spots. The bright lpot on the upper end of Fig. !2, at the planet's north pole, is supposed to be the reflection of light from 81WfD and ice. This supposition is rendered probable by the {act that the spot disappears as the north pole of the planet is turned towards the sun, and returns again with the departure of the direct rays of the 8UD, and the retu rn of winter. The nrface of Mars is variegated with oceans, seas, aod continents, with mountains and vales, like all the rest of the planetary bodies. "On this planet," lays Dr. He~l,"we discern, with perfeot distinctness, the out. lines 0 hat may be continents and seas." The cele. brated ler, of BerHn, constructed a complete map of the surfaoe of Mars, with accurate delineatioDS of its great Datural divisions, as one would draw an outline Dlap of the world Crom an artificial globe. . The color of Mars is red, owing, it is supposed, to the density of his atmosphere, which may color the whole scene, 8S clouds put 'on a gorgeous crimson in the morning or evening sky. This oolor is not merely telescopi" : it is the natural color of the planet as seen by the naked eye; and by it he may easily be distinguished from the fixed stara. 82 • TBLBSCOPIC VIBWS OF SA-TUIlN. THE A.STEROIDS. Of the A steroiu very little is known, on account 0' their distance and their diminutive size. A thin haze, or nebulous envelope, has been observed around Pallas, su pposed to indicate an extensive atmosphere; but no' spots or other phenomena have ever been detected. It is hoped that if ever Lord Rosse returns from examining the distant ne bulle, he will give us some new light respecting the bodies of the Solar System. The Asteroids are never visible to the naked eye. Through a telescope they have a pale ash color, with the exception of Ceres, which in color resembles Mars. 1UPITER. or Fig. 24 is a representation of Jupiter,-the prince planets. His natural color is 8 palish gell.()fJJ. His belt. are seen where they are usually found, namely, on each side of his equator, or in his temperate zones. The map shows his flblate form, or the difference between his polar and equatorial diameter. ' What the belts of Jupiter are is uncertain. " They are generally supposed to be nothing more than atmo. qherical phenomena, resulting from, or combined with, the rapid motion of the planet upon its axis." In number they vary.from one to eight. Sometimes they continue without change for months, and at other times break up and change their forms in a few hours. Dark spots are also frequently seen in these belts, one of which was,;lDown to maintain the same position for upwards or r~f1; years. Lesson· 63. 'lBLBSCOPIC VIEWS OF SATUaN. (Maps 10 and 11.) Fig. 25, Map 10, is a telescopic view of Saturn with his belta and ring,. The helt8 resemble those ot Jupitp,r. already described. His rings will be noticed in conneotion \vith Map 11, to which the student is referred. The I , TELESCOPIC VIBWS OP SA'ft'llK. body or Saturn 83 is of a lead color-the rings a ,U"erg ."hite. Before the invention of the Telescope, Saturn \'188 known only as a distant planet, devoid of that special interest with which modern discoveries have invested him. But since. the powers of that wonderful instrument have been brought' to bear upon him, he has assumed new and resplendent glories, and now stands forth to view as QDe of the most interesting objects in the gorgeous heavens. Though we have no room in this treatise to desc~be the different kinds of telescopes, or to detail their history, we propo~, nevertheless, to give some idea of their imprl1t1sment, by traoing the Iuccessi1'e step. by which we have arriyed at OUf present knowledge of the planet Saturn. The figures arranged across the top of Map 11 are representations of a variety of telescopic views of Saturn, by different observers, during a period of 45 years; Of from 1610 to 1655. The variety in these appearances is probably owing more to the various qualities of the telescopes used, and their general imperfection at that early period, than to any other cause. Fig. 1 is a view, had by Galileo, the inventor of the telescope, in the year 1610. He supposed there were two large satellites at equal distances from the body of Saturn. Fig. 2 represents him as he appeared to Scheiner in 1614. Fig. 3,is a view by Riccioli, in 1640. With the exception ,ot the convexity towards the body of Saturn, the figure is a ~ty~ correct one so far as the rings were traceable. Fil~~epresents Saturn as he appeared to HeZvetiu in 1643. Fig. 5 is another view by Helvetius, in 1649. The rings were now traced much farther than ever before, and thei r existence Q,6 ringa was considered highly probable. Fig. 6 is a third, and still better view, by the same ob• .arvef, in 1650. ' Fig. 7 represents a fourth view by Helvetius, in 1650. Fig. 8 is a most a~curate and enchanting view had by , RiccioIi in 1651. It shows the rings of Saturn as they are often seen in our own times, through telescopes of moderate power. The remaining four representatioDs, ,. j 84 TBLBSCOPIC VIEWS OF SA.TUB.~. 1 as they occur on the map, were all had in 1655: the first by Fontani; the second by Dif1ini; the third by Riccioli; and the fourth by GU8entlu. The real appearance or Saturn, as seen through a common and cheap telescope, is well represented at A or B, immediately under the above views, with the exception of the opening between the rings. We have often seen nim as here represented,-and with the belts across his disc as shown in Map 10,-and that, too, with an ordinary refracting telescope; b~t in earlier periods in the history of the &eience, such views were denied even to the most wealthy. devoted, and profound astronomers. But this wonderful planet does not present the same appearance at all times, even with the aid or the best glasses. Indeed, the better the instrument the more perceptible his variations. In the course or 30 years, the time or his periodic revol ution, he presents all the different phases shown at Fig. 3, from A to H. At one time the rings are entirely invisible, except 8S a dark stripe across the body of the planet, as seen at A. A bout years afterwards the rings appear slightly opened, as at B; and in years more they appear 8S at C, &c These different phases are all accounted for by Fig. 2. Here the sun is seen in his place in the centre, and 'the earth and Saturn in their orbits, as they ,may be supposed to appear to a beholder at a distance, and elevated some. what above the plane of the ecliptic. This diagram may be used to illustrate a variety of principles. ~ 1. It shows how the axis or Saturn (88 well hat the earth, &c.) pre8e",e8 iU paralleli6m in all arts of ita orbit, and from age to age. 2. It illustrates the subject of his .eal0ft8, 8S partially explained ill Lesson 65; and shows how the sun must shine on one side of his rings 16 years, and on the other 15 years. At A the light falls directly on the edge of the rings; but as soon as he passes that equinoctial point, the sun shines upon the lOfDer or 80uthem side of the rings, and continues to tlo 80 til1 the planet reaches its other equinox at E. Here the'light crosses over to the upper or tIDrlA aide of the rings, upon which it continues for the at 3t or ~ TRLESCOPIC VlBWS OF 8A.T11B.N. Dex~ 85 15 yeaN; or till the planet pUaes round to A again. . 3. It shows that the Equinoze. and &laticea are by DO means peculiar to the earth-they belong to all the planetary bodies. In the figure, A and E are the equinoctial, and C and G the 80utitial points. 4. The learner should test himself by this figure to see if he funy understands the subject of the "",,'a declinatWfl, as ex plained in Lesson 48. 5. As before said, this view of Saturn in his orbit accounts for all his different phases during his periodio journey, as shown at Fig. 3. Let the student suppose himself on the earth, where he really is, and watching Saturn in his course; and he will find that the rings must necessarily present all the variety in appearance which is seen in Fig. 3, as well as every intermediate degree of contraction and expansion. Let this explanation be traced through. Take any particular position of Saturn, or take them in order, beginning at A, and it will be found that the view denoted by the correspollding letter in Fig. 3 must be the appearance from the earth, as she comes round between Saturn and the SUD. Ate the rings are thrown up, and hide the upper edge of the planet; while at G they seem inclined the other way, and the planet hides the upper edge of the rings, &0. 6. This diagram shows why we cannot see Saturn at all ti~in the year. Suppose him to be at C, for instance, the first of January, and the earth on the same aide of he orbit; of course he would be directly overhead, or rather on the meridian, at midnight, and might thereror~ easily be seen for six hours preceding, and six following that hour. In six monttJa from that time, or by the first of July, the earth will have passed round to the point opposite G; but as Saturn has moved but a short distance apparently in his orbit, he will not only be above the ~orizon in the daytime, but nearly in conjunction with the SUD. He must therefore be invisible till the earth again gets around \vhere Saturn will ~ comparatively in opposition, or OD the dark side of the earth. d 86 . TBLESCOPIC VIEWS OP SA-TURK. Lesson 66. J)ll\IE~SION8, STRUCTURE, AND USBS OlP SATURN'S RINGI • . '(Map It.) I Diameter of the planet • • I)istance to the interior ring Width ot the interior ring • Openi ng between the rings • Width of the exterior ring "\ External diameter of the outer ring Thickness of the rings • - • 79,000 miles• 20,000 " 20,000 " 2,000 " 10,000 " • 192,000 " 100 " or « Fig. 4 on the map is a vertical view of the rings Saturn, or such as an observer' would have if he were situated directly over either pole of the planet, and at a considerable distancA from it. The opening between the rings, and between the planet and the rings, wou Id then be visible all round, and of uniform width. Through these openings the stars would be as distinct as in any other portion of the celestial sphere; hence we have so represented in the figure. Fig. 5 is a view of the rings as they would appear to an observer 8ituat~d upon the body of the planet itself, and about half way from his equator to his north pole. This is a BUmmer view, of course, as the· rings are en. lightened; whereas during winter in the nortbe# hemi. sphere the rings would look dark, like the da~art of a new moon. Under this gorgeous arcb may be seen a portion df the planet's surface. On the right is a MID moon, and on the left a full moon, both in view at the same time, one in the west and the other in the east. On the left, and crossing the rings, may be seen the shadow of Saturn, gradually ascending the arch as the night advances, till it reaches the zenith at midnight, and disappears ill.· the west at the approach of day. ' Fig. 6 is a similar view from the body of Saturn, t.he observer being located at a distance from the equator, or OF DB.SCBBL AND LB VEIlJUBR. 87 near his pole on the planet's surface. The arch would then appear low down in the south, and also more narrow and slender; and a much 'mailer portion of the rings would appear above the horizon. The following particulars may conclude this interesting lesson. 1. By observing the mot~on of certain spots or in. equalities in the rings of Saturn, it has been ascertained that they reool",e around the planet in 1OJ- hours; or in the time of his diurnal revolution, (LesSon 21.) 2. That the rings are 801id maUer, like the body of Saturn, seems evident from the fact that they reflect the light of the sun very strongly, and cast a deep shadow upon the planet's surface. 3. Stars have sometimes been seen between the inner and outer rings, which proves them to be· actually separated. 4. Of the tuel of these wonderful rings it is sufficient to say that they serve as 80 many reflector, to the pl~net; and being only about..Jt part as distant as our mOOD, and· of such vast maguitude, they must tend grently to modify the climate of the planet, by contributing to the light and heat of his summer evenings. During the winter in each hemisphere, the rings cut a ,hadotD, and increase the intensity of the cold. BB:aSCBEL. U~hiS distant orb no .spots have ever yet been discovere . It is supposed to be surrounded by all atmosphere; bu even this is not oertain. Through a telescope . "we see nothing but a small, round, uniformly illuminated disc, without rings, belts, or discernible spots." It is ot a pale Bsh color. I.E VERRIER. Very little is known as yet of this new member of the solar family. We have therefore attempted no .representation of its telescopic appearance upon the map. By the fOllowing letter, however, copied from the London '1'illle., .a~ 88 TB1"BSCOPIC VIEWS OP LB VERRIER. it appears that Le Verrier also may be adomed with a suit of gorgeous rings: STAB.nJ:LD, Liverpool, Oct. l~, 1846. On the 3d instant, whilst viewing this object with my large eq uatorial, during bright moonlight, and through a muddy and tremulous sky, I suspected the existence of a ring round the planet; and on surveying it again for some tilne on Saturday evening last, in the absence of the moon, and under better, though still not very favorable atmospherical circumstances, my susvicion was so strongly confirmed of the reality of the ring, as well as of the existence of an accompanying 8~tellite, that I am induced to request. you, as early as possi~le, to put the observations before the public. , The teleScope used is an equatorially mounted NewtoDian reflector, of 20 feet focus, and 24 inches aperture, and the powers used were various, trom 316 to 567. At about Bl hours, 'mean time, I observed the planet to have apparently a very obliquely situated ring, the major axis being seven or eight times the length of the minor, and having a direction nearly at right angles to a paralle'l declination. At the distance of about three diameters oC the disc of the planet, northwards, and not. far from the plane of the ring, but a little following it, was situate a minute star, having every appearance of a satellite. I observed the planet again about two hours later, and noticed the same appearances, but the altitude declined 80 much that they were not so obvious. impression certainly was that the supposed s te had somewhat approached, but I cannot positively assert it. With respect to the existence of the ring, I am not able absolutely to declare it, but I received 80 many impressioDs of it, always in the same form and direction, and with all the different magni fying powers, that I feel a very strong persuasion that nothing but a finer state of atmosphere is necessary to enable me to verify the discovery. Of the existence of the star, having every aspect of a satellite, there is not the shadow of a doubt. _ A fterwards I turned the telescope to the Georgium Si. dus, and remarked that the brightest two of his satellites or :tD ,. DISCOVBllY OF THE SBVBllAL PLAlfBTS. 89 were both obviously brighter than this small star aocom· panying Le Verrier's planet. W M. LASSBLL. In the periodical from which we copy, this statement of Mr. Lassell is accompanied by a drawing, representing the appearance of the planet as above described. Lesson 67. OP TUB DISCOVERY OF THB SEVERAL PLANETS. Mercury, Venus, Mar" Jupiter, and Satum, have been known from the earliest ages in which astronomy haa been cu,ltivated. Vesta was discovered by Dr. Olbers, March 29th, 1807. A,trllYJ was discovered by Mr. Encke, ot Dresden, Dec. 15th, 1845. Juno was discovered by Mr. Harding, Sept. 1st, 1804. Cerea was discovered by Piazzi, at Palermo, Jan. 1st, 1801. . Pallu was discovered by Dr. 01 hers, of Bremen, March 28th, 1802. Her,chel was discovered by Sir William Herschel, MarNj3th, 1781. Le. Tier, the Dew planet, was dem01l8trated to eNe ~y M. ~ errier, of France, in August, 1846. Its existence and locality being thus determined, it was first lleen Sept. 23d, 1846, by Dr. Galle, at Berlin. As the circumstances of this discovery are oC the most interesting char~cter, we subjoin the following letter upon the subject Cor the perusal of the student: EIS, near Durham, OcL 8, 1846. But a few months have elapsed since the discovery of .he small planet Astrma,· the companion of the small planets JUDO, Ceres, Pallas, and Vesta, already known. The last few days have brought us the intelligence oltha 8· 90 r DISCOVBRY OP THB SBVBIlAL PLAKBTS. discovery of another new planet, under circumstances 80 unexampled, as to form the most brilliant achievement ot· theoretical and practical astronomy. Some of your read. ers may be interested in a familiar explanation of the steps which have led to this interesting discovery. The motions of all the planets are affected by the gravitation of the planets to one another; and the places of the planets in the heavens are computed beforehand, 80. that the positions given by observation can be constantly compared with those previously calculated. Now the observed motions of the planet Uranus, the most distant hitherto known in our system, when thus compared, were found not to agree with the motions which the planet would ha ve, after allowing for the influence of all the known planets; and when it was found that the deviations were far greater. than any which could be ascribed to mere efrors of observation, that they were of a regular character, and of such a nature as would arise from the action of a still more distant planet, the attention of astronomers was directed to ascertain whether the disturbances· were such a.tJ to point out the position of the disturbing planet. A. long agp as the year 1842, 8 communication took place between Sir John Herschel and the lamented German astronomer, Bessel, on this subject: and there is reason to suppose that some researches on the subject will be found among Bessel's papers; for, in a letter written Nov. 14, 1842, to Sir J. Herschel, Bessel says, "In *~e to our conversation at Collingwood, I announce t u that Uranus is Dot forgotten." The question w , owever, taken up by other astronomers. Le Verrier, in France, and Mr. Adams, of St. John's College, Cambridge, in England, each in ignorance of each otber's labors, proceeded to investigate this most intricate question, and arrived independently at the same conclusion, that the probabl& place of the suspected planet was about 3250 of heliocentrio longitude. This was sufficient to point out, within certain limits, the part of the heavens at which the planet, if visible, would be seen; and, in consequence, Professor Challis, at Cambridge, for the last two months, was en. . ftt~ed in mapping the neighboring stars with a view or ---~---- -..-, - _.--- -- .... -- .- ....... _ .. _. - DISCOVBllY OP THE SBVBRA.L PLANBTS. 91 detecting the planet. Sir J obn Herschel alluded to the probability that the planet would be detected in the speech which he made on resigning the chair at the late meeting of the British Association. Having observed that the last twel vemonth has given another Dew planet to our system, he added, "It has done more. It has given us the proba. ble prospect of the discovery of another. We see it as Columbus. saw America from the shores of Spain. Its movements have been felt, trembling along the far.reach. ing line of our analysis, with a certainty hardly inferior to that of ocular demonstration." The eloquent and glowing anticipation of the future was soon to receive its accomplishment. On the 31st August, Le Verrier made public the following elements of the orbit of the supposed planet, deduced by most laborious calculations from the observed disturbances: or Semi-axis major • • Eccentrioity • • • Longitude of Perihelion Mean long. Jan. 1, 1847 Periodic time • • • Mass. • • • • • . • • • • • J 36,154 0,10761 2840 45' 318 0 471' 217,387 sidereal years. ~. He also announced that the planet would probably present a disc of about 3/1 in magnitude. This an. nouncement reached Dr. Galle, at "Berlin, on the 23d of SepteMlter." and on the same evening Dr. Galle, on com. paring" stars in Dr. Bremiker's chart with the heavens, foft.nd a star of the eighth magnitude which was not marked upon the map. The place of this star was accurately ohse"ed, and on comparing this place with its position on the following night, its motion, amounting to about 40 ,in right ascension, and 301' in declination, was detected; and the star was proved to be the expected new~an~. . It ought to be noticed that the new investigations of Le Verrier, accompanied with a recommendation to astronomers to search for the planet by examining whether any 8tar presented a sensible disc, did not reach Cambridge till September 29, and that Professor Challis, on that very 92 DISCOVERY OF TBB SEVBRAL PLANBTS. evening, singled out one star, as seeming to have a disc, and that star was the planet. Thus the theory, derived by a most abstruse calculation, from long-contin ued ac. curate observation, has been cOlnpletely verified; and a triumph has been gained which will go down to. posterity among the most brilliant of astronomical discoveries. The known boundaries of our planetary system have thus been nearly doubled; a planet is added to it requiring more than 217 years to complete its revolution round the sun; and moving in regions so remote as to recei ve but Iiooth part of the light and heat which our earth enjoys . . It will remain to be discovered whether, as seems most probable, this planet is accompanied with a train of attendant satellites; whether its motions are in accordance with the known laws of gravitation; or whether it, in turn, is to serve as the means of a still further extension of the sol ar system. There is one circumstance connected with this new planet which is too remarkable to be overlooked. It was long since noticed by Bode, that the distance of the planets from the sun follows a peculiar law, \vhich may be thus stated-that if the distance of Mercury from the sun is assumed to be 4, the distance of V en us, the next planet, .is 3 added to 4, or 7; that' of the earth" which is next, twice 3 added to 4, or 10; and thus for the remaining planets, the distances from each other are douhlrvery time, as may be seen from the following tableL' ]V ame of Planet. DiaL from tbe SUD. Meroury • • " • Venus .• • Earth • • • • • Mars. . • • Small Planets • • Jupiter • • • Saturn •••. Uranus . • • • New Planet • • • 4 7 10 16 28 52 100 196 388 Dift"ereocse. 3 8 6 12 24 48 96 192 The distance of the new planet then approximatel,. • OF THB SBCONDA,IlY PllNETS. 93 88.tisfies this very remarkable law; and the little stranger is at once .recognised as bearing a strong family likeness to the other members of our system. TBXPLB ORBVALLIBR. From the calculation submitted in the foregoing ac. counts · it appears that the Le Verrier planet must be nearly three tJamua7lll miUiou of milea trom the SIlD! Verily, such a discovery is "enlarging the boundarie,. the Solar System" most effectually. But what is this distance after all, when we consider that it would re. quire more than 6000 such journeys to reach the nearl18t of the fixed stars , or CHAPTER III. OF THE SECONDARY PLANETS. Lesson 6S. CRAB.ACTBR AND NUXBER OF TRB SBCONDAR.Y PLANETS. (Map 2.) THE aecondary pltJnet.a are those comparatively small bodie8~at accompany the primaries in their course, and revolve '-lund them. As the prirnaries revolve around the sun, so lhe secondaries revo) ve around their primaries. • The n umber of secondary planets positi vel y known to exist is nineteen. Of these, the Earth has one, Jupiter ftmr, Saturn eiglaf, aDd Herschel liz. They may be seen on the map at their relative distances from their primaries. Their relative fIIagmJ:udu are also repra• ~ • ented. 'rhough the secondary· planets have a compound motion, and revolve both around the sun and a round their respective primaries, they are subjeot to the same gen~ral law8 of gravitatioD--<»f centripetal and oentrifugal lorQft 94 OF THE BARTH'S SATELLITE OR MOON. -by which their primaries are governed. Like them, they receive their light and heat from the SUD, and revolve periodically in their orbits, and 011 their respective axes. In the economy of nature they seem to serve as 80 many mirror, to reflect the sun's light upon superior worlds, when their sides are turned away from a mo... direct illumination. The secondary planets are g~Deral11 called moo"", or 8atellika. Lesson 69. SUPPOSBD SATELLITE OF VBNUS. Several astronorhers have maintained that Venul fa attended by a satellite. From the observations of CasBini, Mr. Short, Montaigne, and otbers, as quoted by Dr. Dick,· it seems highly prob~ble that such a body exists. M. Lambert supposed its period to be 11 days, I) hours, and 13 minutes; the inclination of its orbit to the ecliptic 63fo; its distance from Venus about 260,000 miles; and its magnitude about t that of Venus. It is to be hoped that this interesting question will ere long be fully settled, as it is one which numerous telescopes, both in this country and in Europe, have capacity to decide. It is a question worthy of the attention of Lord Rosse, and the powers of his colossal reflector. Lesson 70. / OF THB BARm's SATELLITE 0& MOON. (Map 12.) To ordinary obser~ers of the heavens, the moon is an Object of great interest. Her nearness to the earth-her magnitude-her rapid angular motion eastward-her perpetual phases or changes, and the mottled appearance of' her surface, even to the naked eye, all conspire to arrest the attention, and to awaken inquiry. Add to this her • Celeeti.! Scenery, pp. 84-89. • ..., OP THB BARTH'S SATELLITB OK KooN. 9b conneotion with Eclipses, and her influence in the product.ion of Tides, (of both of which we shall speak hereafter in distinct chapters,) and she opens before us one of the most interesting fields of astronomical research. The following table exhibits the principal statistics and facts respecting the Dloon, and should be carefully Bt.udied or committed to memory. Mean distance from the earth's centre 240,000 miles. Sidereal revolution 27* days. Synodic revolution 29i " 13 Periodic revolutions per year, nearly Direction in orbit from west to east. Hourly motion in orbit - 2,300 miles. Mean angular motioll per day 130 101' 351'1' Diameter. - 2,160 miles. A pparent angular diameter • 311' 71'1' Bulk, as compared with the earth • Bulk, as compared with the sun 1'15 , ,1r1r1 Surface, as.compared with the earth • Density, the earth being 1 i 0 Inclination of orbit to the ecliptic 0 9' Eccentricity of orbit - 18,833 milel. Longitude of ascending node variable. 1!0 Inclination of axis to orbit Revolution upon axis 291 days. LIght reflected by her, as compared ·~h that of the sun -. 3 0 I., ~ 0 4 8y c~aring the distance of the mOOD, as expressed in the foregoing tobie, with that of the sun, (Lesson ~t) it will be seen that the latter is four hundred times as far off as the former. It is for this reason that she generally appears as large as the sun, when in ract he is seventy million times the laTgest. The moon may therefore well be regarded as our nearest terrestrial neighbor. It may also be interesting to compare the angular fll4gnitude of the moon as seen from the pardi, with that of the sun, as given in Lesson 11. They seem to differ but D:~N; or less than one minute of a degree. Thus the eun, on acoount of his immense distance, looks no larger , .1 1 j i 96 CHA.NGES OR PHASES OF THE MOON. than the moon 'j when in fact he is equal in bulk to 8toenty "li.llio1l8 of such bodies. If the student does not fully understand the caae this agreement in the apparent magnitude of the sU,n and moon, when they are in reality so diRproportionate in bulk, let him turn back and review LeSSon 10, and the map and figure therein referred to. or Lesson 71. CHANGES OR PHASES OF THE MOON. (Map 12.) The upper row of figures ,on the map represents the changes of the moon in passin"g from new to full moon, and around to new moon again. The first figure on the right represents the new moon, wben, if visible at all, we see only her dark sid... She is then at her conjunction, or in the same longituc.e with the sun, and to ordinary observers is in visible. As she advances eastward in her orbit, she falls behind the" sun in his apparent daily course, and in a few days is seen in the west just after sundown, in the form of a slender crescent, as seen in the next view to the left. As she advances, we see more and more of her bright side, as represented on the map, till she reaches her t1ppOrition, when her en)~· htened hemi. sphere is towards us, and we see her as a id~: From this time on ward the !Deat side 0 the loon begins to be obscured, Cor want of the sun-Ii t~ an.d the crescent begins to be inverted. From the first quarter to the full, and from full moon to the last quarter, the moon . , is said to be gibboua. The cQ,ue of these changes is further illustrated in Figure 2, where the earth is shown in the centre, and the moon at various points in her orbit., The sun is "Supposed to be on the right, as in Figure 3. The outside suit o( moons shows that in fact just one half of the moon is always enlightened; while those on the inside show IwtD much and which part of her enlightened aida !a , .... ~ TO KOOK'8 P~TB ABOUND TBB 81m. 97 flUlJJle frD7A ,At. earlA. A is the new moon. B shows her when first visible. C is the first quarter;. D gibbous; E full mOOD; F gibbous; G last quarter; H the crelWent inverted; and A new moon again. This revolution the' mOOD around the earth, is called a lUfiation. The poiJIts A and E, in the moon's orbit, are calJed her qzggiu; C and G her quadrature.; and B, D, F, and H, her ocIanU: or LeSBOD 7g. '1'JD KOOK'S PA.TH A.ROl1ND TBB SVIf. (Map 12.) The revolution· or the moon around the earth, and with the earth around tbe 8UD, is represented by Fig. S.* As her orbit nearly coincides witb the ecliptic, she is some· times IllitAiA, and at othel"8 fllithout the earth's orbit. When the moon is at A, and tbe eartb in her orbit between A and 19, it· is fttID mDmI. In about 14 days she reaches B, and will be seen (rom the earth &8 a full ftlOOfi. In 14 days longer she reaches C, when it is new ·moon again, , and 80 00 perpetually. At A she is in conjunction, and at B in 0pp08ition. But it will be seen that the twelve revolutions of the mOOD and the one revol ution of the earth do fIOt come out ft1eft; or in otber words, do Dot end at the same time. From tbe new moon at A, around to the new moon at D, are ~ twelve lunar mODths or revolutioDs; but at this time earth wants 19° 2(Y to reach her starting-point • The author ill aware that the figure doee not repreeeDt the actual path of the ~Q around the 8UD, neither i8 it pcaible to draw it, except upon a fery large &Cale. The moon ,.~~er retrogradt., but i8 advancing "i~ the earth at the rate of 65,000 miles aD bour, even at new moo', and when falling behind the earth. When in oppoeitiol1, and pining upon the earth, her velocity .. about 71,000 miles an hour. The true path ol the moon would appear a)mOBt pllraJlel to that of the earth, which it would CI'088 backward and forward, at ..ery acute aarlee, every 141 day., or at iDtervale of about 1410 each. But even the portion witli'll the earth'8. orbit would b, conca~, to.Md. tAe nn. The diagram, Fig. 3, inculcatee more tntA aJld Ie •• .,..,.or thaD any other Wf'J could employ, aud we Ule it for the ..me I'8UOn that we find it in Burritt'. Atl.., ad ill Mitchel'. editiOD of 1M Geopaphl of &he Ilea.... . . 8 98 1 REVOLUTION OF THE l'tIOON'S NODES. at A, or to complete her year. ·The lunar year, there. fore, consisting of twelve synodical revolutions of the mOOD, or 346 days, is 19 days shorter than the civil year. Lesson '2'3. llBVOLUTION OF THB MOON'S NODES AROUND THB BCLIPTIC. (Map 12.) , By referring to Lessons 30 and 31 it will be seen that the nodes of Mercury and Venus are permanent; that is, that they are always at the same point in t~e ecliptic, or in the same longitude. But this is not the ol¥e with the moon's nodes. Suppose the line passing down from A, Fig. 3, to represent the line of her nodes, at the commencement of a lunar year. After twelve Iunations, and when she has passed round to the point D, she will ha ve returned to the same node again, ·although she is 19° 20' short of the point where that node was reached 846 days before. At this time the line pa.~sing down from D would represent the line of her nodes. In this manner the nodes of the moon's orbit fall back westward, or recede 19-j-° every lunar year, till they complete a backward revolution quite around the ecliptic. To do this requires 18 years and 225 days, or 223 Iunations ; when the moon will reaoh the same node again at D, or in the same longitude. ~-. This revolution of the moon's node~ will be nqticed again in the chapter on Eclipses. The motiT of"th941prides will also be e·xplained and illustrated inlhe 5aptqr on Tidu in connecdon with Map 14. . ) , I ,' . . Lesson 74. I. SIDERBA.L A.ND SYNODIC REVOLUTION OP THB KOON. (Map 12.) The difference between a sidereal' and 6ynodic revolution of the planets is explained in Lesson 57. A 8itlet'eal I THE KOON'S J..IBJU.TIONS. II J 99 revolution or the moon is a revolution from a partio1:llar star, around to the same star again; or what would con. stitute a complete revolution if the earth. were at rest. But as the earth is constantly advancing in her orbit, the mOOD, in passing from one full moon to another, has to perform a little more than a complete revolution to bring her again in opposition to the sun. This extended jour. ney is called her 8yraodiC revolution. The sidereal period is 27} days, and the synodic 29i, as already stated, Lesson 70. . Lesson 73. REVOLUTION OF THB MOON UPON BEB. A.XIS. "' ~. (M~p i2.) From the uniform appearance of the moon's surface, even to the naked eye, it is obvious that she always presents Dearly the same side to the earth. From this fact it is concluded that she makes but one revolution upon ber axis during her synodic revolution-that her motion upon her axis is from west to east-that her day (including a lunar day and night) must be equal to 29j of our days; and that the earth is always invisible from ODe half of the moon's 8urface. By consulting Fig. 2, it will easily be seen that to keep the same side towards the earth, the moon must necessarily _olve once on her axis during her synodio revolu • .tion; and also that if the side towards the earth at the full W8:8 t~ardl us also at new moon, the side in darkness at full mc!oa fbUld be towards the sun, or enlightened at new mooll~t Observe, we are speaking of her actual light and shade, jm.d not of her appearanoe from the earth• . I Lesson '0. THB KOON'S LIBRA-TIONS. , . (Map 12.) . Though the moon always presents nearly the same hemisphere towards the earth, it is Dot always preci6el, 100 TBLESCOPIC VIEWS OF THE IIOON'. the same. Owing to the ellipticity of her orbit, and the consequADt inequality of her angular velocity, she appears to ,.,11 a }·itile 00 her axis, first one way and then the other, thus alternately revealing and hiding ne\v ter. ritory, as it were, on her eastern aDd westem limbs. This rolling motion east and west IS called her lihratiOfl in longitude. The inclination of her axis to the ecliptic gives her another similar apparent motion, alternately revealing and hiding her polar regi0ft8. This is called her libratitm in latitude. It may be illustrated by Map 4, Fig. 2, as explained in Chapter VI. Lesson 7'. SEASONS OF THE KOOK. or The moon's year consists of 29} our days; and as she revolves but once 00 her axis io that time, it follows that she has but one day and one night in her whole year. So slight is the deviation of her orbit from the plane of the ecli ptic, and the inclination of her axis to the . plane of her orbit, that the 8UO'S declination upon her can never exceed 6 0 40/ • She must therefore have perpetual winter at her poles, while at her equator her long days are very warm, and her long nights very cold. Lesson '8. , TELESCOPIC VIEWS OF TBB KOOK. - (Map 1.2.) , Fig. 4 is a telescopic view of the moon, 88 slle apPears when about a week old. The ragged line dividing her ill uminated from her dark hemisphere, and extending around the mOOD, is called the circle of illumination,. and the portion of this circle towards the earth, as represented on the map, is .called the Terminator. This line traverses the moon's disc from west to east in about 15 days, when PBYSIC~L CONSTITUTION OP TB8 MOON. 101 it disappears from her eastern limb; and the other haIr of the circle of illumination inlmediately appears on her western border. In about 15 days longer,' it passel around to the eastern limb agaill, as represented at Fig. 6, and at the change of the moon entirely disappears. The Figures 4, 5, and 6, are faithful representations of the mOOD, as she appears through a telescope of moder- . ate power, at three differeDt periods during a lunalion. Lesson 79. PHYSICAL CONSTITUTION 0 .. THE MOON-MOt1NTAI1fI, VOLCA.NOBS, ATMOSPHERB, BTO. (Map 12.) Nothing is more obvious, from a telescopic view of the mOOD, than that her 8U rface is remarkably rough and u . . ~en. The evidence of this is, Firat, the crooked aod ragged appearance of,the termifllJtor. Were the moon's surface level and smooth, thia line would be uniform, aDd sharply defined. In the 8econd place, small bright spots appear from time to time, from new to full mOOD, beyond the terminator, in the dark portions of the moon's disc. These are nevll far from the terminator, and grow larger and larger as i~proaches them. In the same manner these bright spots linger after the terminator, from full to De·w mOOD, and grow ffIIlaller and smaller till they disappear. In the ';'ird place, after these spots fall fairly within the enJigh:ened hemisphere of the moon, they project a .1&atlouJ towards the terminator, or in a direction opposite to the 8U~. From new to full moon these sha~ow8 aU point etJ8tUJard, while from full to new moon again they all point ree#uKJrd. N ow nothing can be more certain, from all these phe. nomena, than that the moon is covered with mouftllJiflf. Being elevated above the common level of the moon'. surface, the sun's light would fall upon their summits be. fore the 8urrounding valleys were rendered luminous or 0* 102 r· • PHYSICA.L CONSTITDTIOlf 01' THE lI00lf. visible by reflected light. As the light advanced eastward it would enlarge the visible portioD8 of the moUDtaios; and finally, after the space around them, west, Borth, and south, W88 enlightened, they would still cast shadows eastward. Besides, these shadows are always darkest on the side towards the SUD, or nearest the moUDtains. By extlmining Figures 4 and 6, in connection with the foregoing remarks, the student can hareHy fail to be satis. fied that the moon also has her Alps, her Andes, and her Pyrenees. Some of her mountains have been estimated to be five miles in height. It has been ascertained also that many of the lunar mountains are of fJolC4Ric formation, like Etna and Vesuvius. Dr. Herschel states that he actually saw the light of the fire. of several active volcanoes in the moon. The extravagant statement made by some authors, that cities, fortifiCati0n8, and rotlll8 have been seen on the moon's disc, is worthy o.f little or no credit. It is much easier ~ imagine cities, &0., to exist on the moon's surface, than to actually Bee them even if they were t~ere. In regard to the existence of 8n atmosphere around the moon, astronomers are divided. From observations during eclipses of the sun, and other phenomena, it is thought that if the mOOD has any atmosphere at all, it must be very limited in extent, and far le88 deose than that ot the earth. t/IJ Dr. Scoresby, of Bradford, England, has published a description ot the moon, 88 ~he appears tarough the monster telescope of L9rd Rosse. He repreS«¥lts her as appearing in great magnificeoce. through this famed instrument, seeming like a globe of molten silv~r, whilst every object or the extent of one hundred yprds was quite visible, and edifices of the size of York Minster. might therefore, he said, be easily perceived ~f they had existed. He states however, that th~re was no. appearance or any t}ling of that nature, neither was there any indications of the existence of water, nor of an atmosphere. There was a vast Dumber of distinct vol. canoes, several miles in breadth; through one of them .. 103 GBOGUPJIY OP TO .00lf. there was a line in continuance or ODe, about ODe hUDored and fifty miles in length, w bich ran in a straight direction like a railway. The general appearance, how. ever, was like one vast ruin of nature; and many of the pieces of rook, driven out the yolcaooea, appeared to be l"Jd at various distances. or Lesson so. GBOGRAPHY OP THB KOON, 08 ULBKOGJU.PBY. (Map 12.) The great natural divisions of the moon', disc have received appropriate names. The following is a list 8Ci)me of her principal mountaiu, and their height, according to the recent measurement Mldler: or or Peat. .n.. Posidoniu8 • • • 19,830 8.76 Tycho • • • • 20,190 3.83 Calippus . • • 20,300 8.86 Casatus. • • • 22,8] 0 4.32 Newton. • • • 23,830 4.52 Clavius. . • • 19,030 8.60 ,Huygens • • • 18,670 8.54 Blancanus . • . 18,010 8.41 Movetus. • • • 18,440 8.49 The folfowing list may be found upon the map, Fig. Dt the ~umbers in the drawing answering to those of the table. It may require a Dear view to read the figures OQ the map. 1. Tycho, 6. EratoetheDel, 2. Kepler, 7. Plato, S. Copernicus, 8. Archimedes, 4. AristarehuI, 9. Eudoxua, o. Helicon, 10. Aristotle. The dusky portioDS formerly suppal8d to be- . . ., aN clMignated 88 follows:- • 104 A. Mare Humorum, E. Mare Tranquilitatie, B. " N ubium, F.,," Serenitatis, C. "Imbrium, G . " Fecunditatis, D. " Neotaria, H . " Crisium. MM. Baal and MadIer, of Berlin, have constructed a map of the moon, which is characterized by ProfeSsor· Nichol of Glasgow, as "vastly more accurate than any map of the earth we can yet produce," and 8S "the only authentic and valuable work of the kind in existence." Fig. 0 on the map is a faithful transcript of this invaluable drawin~ of the moon's surface. The subject of Ecl"paea and Occultationa will be con. sidered in Chapter IV.; and that of Title8 in Chapte~ V. • Lesson 81. ... KOON8 0 .. SA.TELLITBS OF lUPIn. (Map 2.) I ,I Jupiter has rour satellites, whose distances, magnitudes, and periodic times are as follows:-They are numbered in order, beginning with the one nearest to their primary. Diameter in Dlltance. Periodic Umee. 2,500.. 259,000.. 1 day 18 hours. 2d 2,068.. 414,000. . 3 " 1241' 3d 8,377.. 647,000. . 7 " 14 cc 4th 2,890.. 1,164,000 . • 17 ". 0 " By comparing t~e magnitule" or Jupiter's satellites, with that of our mOOD, Lesson 70, a striking resem,blance will be discovered. Indeed the Bize and diBtance · of the first &Dswer almost exactly to the size an4 distance of the moon. But when we come to the ptriodic timu, we find a vast disproportion •. So great is the mass and attractive (orce of Jupiter, that if even his most distant . satellite had a periodic revolution of twenty.nine and a. half days, its centriJ>etal would overcome its centrifuJ!'al three, and it would Call to the body of the planet. To balance the great aUractive foroe the planet (Le88OD 1st • mil.. or , ',. '1 8ATBLLID8 OP SAnmK. . 106 17) it is necP.88ary that his secondariee .hould haye a rapid projectile motion; hence, though the first is .. large, and as distant (rom Jupiter as our moon is from the earth, it revolves more than fifiem tiaI. as rapidly .. the moon. For remarks on the centripetal and centrifu. gal forces, see Lesson 20. , \ ,The mOODS of Jupiter revolve nearly in the plane his equator, and of course, nearly in the plane of hia orbit and of the ecliptic. See 82 and DO. Their orbits, as stated by Dr. Herschel, are inclined to the plane his equator, as follow8: , . 1st • • • • • • . So IS' 30". -2<1 • • • • • • Variable. 3d • • • • • • • Variable. 4th • • -. • • • • 2 0 58' 48". The eccentriciti~s of the lit and 2d are not per. ceptible. That of the 3d and 4th is 8mall, and va riable, in consequence of mutual perturbations, caused by tbeir • mutual. attraction. They all reyolve from west to east. or in the· direction of the revolution of their prima-ry upon his axis. ' The satellites of Jupiter may be seen with a telescope of very moderate magnifying power, or a oommOD spyglass; and one of them has even been seen with the naked eye. This Doble planet with his retinue of moone is. t~e solar system in miniature; and furnishes the moat . glor\us confirmation of the' truth of the Copernioan -, theory. For eclipI68 Jupiter's satellites' see the chapter on eclipses. . • or or t r or Lesson Sg. SAT~LLITBS OF SATUB.N. , (Map fl.) The satellites of Sat)lrn are eight in number,· and are seen only with telescopes of cODsiderable power. They revol ve from west to east. The orbits of the six interior • The eigAth baa recently been di8covered. 1(J6 SATBLLITBS 0.. S~TUaN. satellites are MGrly circular, and very nedrly in the plane of the rings. That of the seventh is considerably inclined to the west, and approaches nearer to coincide with the ecliptio. Of the new one little is known. Their distanoes and periodic times are 88 follows:DiaL in mileL 1st 2d 3d 4th 5th 6th 7th 123,000 168,OQO 186,000 251,000 351,000 811,000 2,366,000 Periodic times. • • . • - o days 22 hours. 8 " 1 " • 1 " 21 " • . 2 • " 17 " 4 " 12 " 15 " 22 " - 79 " 7 " • Upon this subject aD eminent astronomer remarks, that tbe satellites of Saturn have been much less studied than those of Jupiter. The most distant is by far the largest, and is probably Dot much inferior to Mars in size. Ita orbit is also materially inclined to the plane of the rings, with which those of all the rest nearly coincide. It is the only one of the number whose theory has been at all in.' quired into, further than 8uffiQes to verify Kepler's law of the period ic times, which holds good in this as in the system of Jupiter. It exhibits, like those of Jupiter, periodic defalcations of light, which prove its revol ution on its axis in the time of a sidereal revolution about Saturn. The next in order, proceeding inwards, is tolerably conspicuous; the three next very minute, and reqllA'ing pretty powerful t~le8C0pe8 to see them; while the two interior satellites, which just skirt the edge or. the rings, • and move exactly in their plane, have never been discov .. ered but with the most powerful telescopes which human art has yet constructed, and the~ only under peculiar circumstances. A t the time of the disappearance of the ring (to ordinary telescopes) they have been thread. ing like beads the almost infinitely, thin fibre of light, to which it is then reduced, and for a short time advancing ". . seen· • By Sir William Henchel, in 1189, with • reSecting telc.cope aI See engraving, p. 161. IMIr feet in aperture. SATELLITB OF LB VEl1B.IEB'S PLANBT. 107 off it at either end, speeding to return, and hasting to their habitual concealment.* Lesson S3. ' SATELLITES 01' HERSCHEL. (Map 2.) , Herschel has .;z satellites, as shown on the map, which revolve around him at the distances here laid down, and in the following periodic times : Dist. in miles. 1st 2d 3d 4th 5th 6th 224,000 296,000 340,000 390,000 777,000 1,556,000 - - - - - Periodic times. days 21 hours. 8 " 17 " 10 " 23 " 13 " 11 " 38 " 2 " - 117 " 17 " I; - -- The satenites of Herschel are ~tillguished by two very remarkable peculiarities. By Lesson 32 it will be seen that his orbit very nearly coincides with the ecliptic. Now the orbits of ~is satellites, instead of being down Deal. the plane of the ecliptic, as is the case with those of J upiter, are elevated so as to cross it at an· angle of near 80°'. In the second place, while every other· planet in the Sol~ System, prim,ries as. well as seoondaries, revolves rrollllvest to east, the satellites of Herschel have a retro. grade or back7Dard revolution. This singular anomaly is indicated qp the rna p by the direction of the arrow I. The orbi:Lr of Herschel'8 mOODS appear to be nearly circular. , Lesson 84. SUPPOSED SATELLITE OP LE VERRIER'S PLANET. From the observations of M. Lassell, as detailed on page 88, it is not improbable that this newly discovered • HeJ'lChel'. Treati8e. 108 ••WD dD OA.llUS OF BCLIPSES: world is attended by one or more secondary bodies. Indeed we might almost lnCer this froID analogy, especially when we consider tbe rttagftitudc of the planet as answering pretty nearly to that of Herschel; and his immtm8e tli8tanu from the 8UD, upOn which he also must depend for light aDd heat. This latter circumstance alone would seem to demand a profusion of moons to arrest the sunbeams in the surrounding space, and reflect them upon the cold and cheerl881 bosom of their primary. For the present, however, the learner must content himself witlt the little we are. able to commuDicat~ upon thi~ subjeot. in the hope that future observations may furnish U8 with a more satisfactory knowledge of the economy and peculia rities of this tar.distant ore. The secondary planets are all supposed to levol v~ on their respective axes, in the time of their periodic revolu. tions, 80 as always to present the same hemispheres to their respective primaries. No smaller bodies have ever been discovered revolying around the .atellite., as mOOD8 or satellites to tliem • .. CHAPTER IV. rmLOSOPHY OF ECLIPSES. #" Lesson 83• • •",.R8 .ND CAUSBS OF ECLIPSES. (Map 13.) AN Eclip.e is the partial or total -ob8curalitm or darlt. ening of either the SUD or mOOD. An eclipse ot the SUD is caned a Solar eclipse, and that of the moon a LuRtJr eclipse. "To undentand the nature and philosophy eclipses, it will be necessary to heBin with what is oalled tAe law ./aad,ow. The prinoipla. ofthia law are as follow8:- or oJ 109 KATURE AND CAUSBS Of BCLIPSES. or 1. A.ltJd,ou, is a portion' of space deprived light by the i~terventioD of some dark or intransparent body. 2. The ltmgth and form of. shadows depend not onl,. on the form of the opaque body, by which the light is in. tercepted, but also upon its magnitude as compared with the luminous body; and its distance from it. At Fig. 1 the SUD is seen at S, on the right, the earth at B, and tbe moon at A and C. The shadows of the earth and moon are seen projecting to the left, and running to a point. They have this form because the earth and moon are 8fIItl1le,. than the 8un; and as the earth is a globe, her, .hadow assumes the form of a cone, with its base towards the sun. 3. If the earth were jut as large as the sun, her shadow would be in the form of a cylin'der J. and if larger than the .un, it would spread out like a fan; or like the section or a cone with its base turned from the sun. These principles may be illustrated at leisure by a candle and several balls of different sizes. 4. When the opaque body is amo11er than the luminous one, the length of its conical shadow will depend upon ita distanoe from the ,source of'liaht. Thus, if the earth were at E, Fig. 1, her 'shadow would be shorter than represented in the figure, by one half. ~. The shadow cast by the earth is darker in some patts than in others.' This is represented at 0, and P P, F~ 2. The deep conical shadow shown at 0, and in a1tlae other figures, is called the Umbra; and the faint .&hadow shown at P P, the Penumbra. We are.now prepared to state the cafUel or eclipses: 1. .An Eclip6e oj- the BU1I is caused by ,the moon passing between the earth and the sun, and cRsting her shadow upon the earth.' This is represented at A, B, Fig. 1, . where the moon is seen passing in her orbit around the earth, and hiding part ot" the sun's disc at S, from the ob. aerver at B; or, what is the same thing, casting her .hadow upon the earth at B. As the moon is moving eaatward, or in the direction of the arrows, she covers the lower tD8Item limb the sun first, and advances to the eut. By turning the right side of the map uppermost {or 10 or or 110 CHARACTER, ETC., OF SOLA.R BCLIPSBS • . a momPDt, and placing it to the south of the learner, the figure. can hardly fail to give l)im a correot idea or the manner in which a solar eclipse is produced, and the reason why it always commences OD the sun's western limb. 2. Eclip,e8 cif tlte moon are caused by her railing into the eart1&'. shadow, as represented at C. Th~se always commence on the moon's eutem limb, as may be shown by turning the left side of the map uppermost. 8. In its natural position the map illustrates another fact: it shows why eclipses of the sun always happen at ftefD mOOD, and eclipses of the moon at full mOOD. To an observer on the .earth the moon must be ReID at A, and full at C. · Lesson S6. CHARACTER, EXTENT, AND DUllA.TION OF SOLAR ECLIPSBS. (Map 13.) 1. The first thing to be determined in regard to solar eclipses is the length of the moon's shadow.;. Let the student now call to mind the 'fact that the earth and InDOD both move in elliptical orbits, as stated in Lessons 43, '5, and 70. Let him remember also, that the sun is in doe of the foci of the earth's orbit, as represented in Fig. e : and that the earth is in one of the foci of the moon'8 ~£jt. a8 shown at T and U. Now as the earth is farther..Pom the sun at U than at' T, her shadow will be longer; and 80 with the moon. The shadows of both are much longer when the earth is at or near her aphelion, as at U, then when near her perihelion, as at T. 2. The length of the moon's shadow is also modified by her position in her orbit. As her mean distance from the earth's centre is 240,000 miles, she must be 480,000 miles nearer the sun at new moon, than at her full. This difference in her distance must haveits effect in lengthening or shortening her shadow. At T, Fig. 2, the earth is at her perihelion, _nd her shadow and that or her aatel.. lite are comparatively short. At U the earth is at her J' - --- - CHA.RACTER, BTC.J OP SOLAJ1 BCLIPSBS. III most distant point from the sun; and the shadows of both the earth and the moon are proportionally elongated. 3. A third circumstance modifying the length ot the moon's shadow, is the position or Aer apAeliOft and periMlion points, in respect to the SUD. When the earth is at T, in her orbit, and the moon at her aphelion at M, whioh is then t,otDQ,rtl8 the 8un, her shadow is the shortest possible; as she is then ft&Jrtr the aun than at any other time; but when the earth is at her aphelion at U, and the moon comes to her aphelion when it. is turned from the sun as at K, her shadow has its greate.t possible length. Such is the variety or causes whioh conspire to afFeot the length of the shadows projected by the earth and moon. 4. When the earth is at U, and the moon at her perihelion, and in conjunction as at H, her shadow will exteqd 19,000 miles beyond the earth; and 'Will be nearly 175 miles in diameter at the distance of the earth's sur. face. Consequently if her shadow fall. centrally upon the earth, it will cover an area 175 miles in diameter, within which the sun will appear totally eclipsed. At this time the ptmumbra will cover,an area 5,000 miles in diameter, w" in which the eclipse will be only partial. It the 8 dow falls upon the ride of the earth, it will or course o er a much larger space; and in either case, it will m e from west to east over the earth's surface. When the earth is at T, and the moon at M, the aha ow ot the moon will not reaoh the earth by 20,000· miles; and when the SUD and moon are at their 'mean distances -from the earth, the cone of the moon's shadow will terminate a little before it reaches Ute earth's surface. 6. The angular or apparent magnitude of a body depends much upon its distance from the observer, (Les80'0 10.) When the sun and moon are at their mean distances, they appear nearly ot a si~e; but when the earth is at U, and the moon at H, the moon appears larger than the SUD, and if a central eclipse take place, it will be total; or, in other words, the moon will en. tirely cover or hide the sun'a race. This is owing to the , 112 CIUJU.CTEa, BTC., OF SOLAa BCLIPSBS. or or nearness the moon to the eartll, and the distance the sun. A total eclipse may last 7 minutes and 58 seconds. 7. When the earth is at T, aDd the moon at M, the IUD, being at his perihelion distance, will appear Ufl1U1IalI, large j and the' moon being in apogee, will appear unfUU,Q,lly amall. Should. a oeotml eclipse happen at. this time, the moon would Dot be Jarge enough to hide the en. tire face of the 8UD, evelJ when '<lirectly between us and him; coDsequently in the middle of the ecUpse the mOOD would be seen covering the centre of the 8UD, and lea villg a luminous ring unobscured, as represented at V on the map. This is ca.lled an QllAular eclipse; and the ring may last 12 minutes and 24 seconds. 8. For convenience in describing eclipses, the diameter of the sun and moon, respecti\rely, is divided ioto twelve parts called. digi,tB. Thus at W, the sun would be delCribed as about three digits eclipsed j at S, about four d~i~&c. . The learner will now understand the difference between partial and total, eentral and annular eclipses. Both anDu]ar aod total eclipses must be central, but the annular eclipse is not total. The ring or outer border of the is left uoobscured. _ "The following is a list of all the solar eclipses t will be visible in Europe and America during the e. mainder of the present century. To those which ill be visible in New England .Ute number of digits is an· nexed. 'flO jf Y88I'. 1847, 1848, 1851, 1854, 1858, 1859; 1860, Kon&b. Oct. Mar. July . May Mar. July July DiaitL Day aDd Hour. 9 1 o A.. x. 5 7 .50 28 7 48 26 4 26 15 6 14 82 29 I) 18 7 23 A.. A.. P. A. P. A... It. M. M. K. x. x. 6t 8t lit It 2i 81- .... 113 CHARACTER, ETC., OF SOLAR BCLIPSBS. Year. Month. 1861, 1863, 1866, 1866, 1867, 1868, 1869. 1870, 1873, 1874, 1875, 1876, 1878, 1879, 1880, 1882, 1885, 1886, Dec. May Oct. Dot. Mar. Feb. Aug. Dec. May Oct. Sept. Mar. July July Dec. May Mar. Aug. Aug. June June Oct. Mar. Aug. July f!.87, 890, 891, , 1 892 t:m· 96, 1897, . 1899, 1900, • June May Da, aad Hour. 31 7 17 1 19 9 S 11 a 3 23 10 7 6 22 6 26 3 10 4 29 5 25 4 29 4 19 2 31 7 17 1 16 o 29 6 18 10 17 3 60 20 o 26 4 9 0 29 9 8 0 28 8 or DIIItL 80 A.. K. P. K. 4j 10 12 A... x. A... K. A... K. A.. x. A.. K. A.. x. 8f o o o 21 o o A. M •. o A. K. 56 11 56 101 A.. K. IIi P. Ji. P. M. A.. M. A.. M. 3f 71 o 30 o A.. M. 35 30 0 A.. M. A. P. K. A.. M. x. o o o Mer. 19 P. x. o A.. M. ot 6i 01 8! o Mer. A.. x. 9 A, x. 8 o Mer. 'i 11 The eclipses 1864, 1869, 1876, an.d 1900, will be very large. In those of 1858, 1861, 1873, 1875, and 1880, the .fUR tDill rile eclipletl. Those of 1854, and 1875, will be annular. The aoholar can continue this table, or extend it backwards, by adding or subtracting the Chaldeao period of 18 yean. 11 day., '7 hours, 54 minutes, and 31 seconds.·!' • Ferg.oa. 8* 114 ZCLIPUS 01' THE KOON. Lesson 87. BCLIPSBS OP THB llOON. I' (Map 13.) 1~ The average length of the earth's shadow is 860,000 miles; or more than three times the moon's average distanoe from the earth. Its average breadth at the distance of 240,000 miles'· (rom the earth's centre, or where the moon p8.88e8 it, is about 6,OO~ iniles; or three times the moon's diameter. Now the exte~ and duration of a lunar eclipse must depend upon these three circumstances: (1.) The distance of the eartA from the auft, and the oonsequent length of her shadow at the time.· (2.) The distance of the ~Oft from the earth, which determines the diameter of the earth's shadow where the mOOD passes it; and (3_) The manner in which she passes through the earth 8 shadow .. If it be greatly elongated, it will be proportionably larger at the average distance of the moon's orbit; and if the moon is in perigee, tlnd passes central', through the earth's shadow, as at G and X, Fig. the eclipse will be total, and long continued. On the ther hand, if the moon is in apogee, she will pass the e rth'a shadow where it is comparatively slender, as at ! and the eclipse will be of comparatively short duration. So if she pass through the aide of the shadow, instead its centre, the eclipse will be partial instead of total. An eclipse of the moon c~n Dev~r be anntllar, as she cannot get 80 Car ofFthat the earth's shadow would be iDe sufficient, when centrally passed, to cover the whole the moon's disc. 2. Before the moon enters the earth's shadow or umbra, as at 0, the earth begins to interoept from her portions of the sun's light, or to cast a faint shadow upon her. This shadow, called the moon's penumbra, grows darker and darker as ahe advances, till she enters the conicnl and perfect shadow of the earth. Here tbe real eclipse begins. The umbra and penumbra may be IIeeIl i-t 0, and P P, on the map. or or TIll. A.ND FaXQl1ENCY OF ECLIPSES. LeS801 J16 SSe OF THE TIME A.ND FREQUENCY or ECLIPSES. (Map 13.) 1. If the moon'. orbit lay in the plane or the ecliptic, as represented at Fig. 1, there would be two celltral eclipses every month j viz., one of the sun and one or the mOOD. But as the moon's orbit is inclined to the ecliptic at an angle of 50 9', (Lesson 70,) it is evident that she may be either Q,lHme or 6eloJD the ecliptic at the time of her conj unction w\th the sun; 80 that she will seem to pass either aiHme or belOUJ him, and will not cause an eclipse. This will be understood by oare fully • observing the moon's orbit at M and H, Fig. 2. At M, the side towards the sun appears t,hroum, up or ab~e the ecliptic; while at H it is hew., the ecliptic. Of course, then, the mooD's .laadouJ wUl pass belOUJ the earth, as represented at H; and though it be ever so long, there "il~ be no eo~ipse. For the same reason, the moon may either above or below the earth's shadow, at the · e of her opporititm, and no lunar eclipse occur. • It is only when the moon is at or near one' of her ., that either a solar or lunar eolipse can occur. o the Map; Fig. 2, the line L N represents the line of the nod~ 88 well 88 the plane olthe ecliptic. At A, the , moon is seen coming to her node, in the direction of the arrow, and castiog her shadow upon the earth. At the same time we see the e.clipse advancing in the same· direction, commencing upon- the sun's western limb at W. At G ud X, in the same figure, we see the moon totally eclipsed. If, therefore, the earth and the mOOD reach the line. of the moon's· nodes at the same time, the eclipse will be central, whether it be of the 8un or moon. 3. But it is not necessary that the earth and mOOD Ihould be precilel, on the line of the moon'. nodes, in order to produce an eclipse. U The distance of the mooD from her node when she just touches the shadow 116 TIll. AlfD PJ1BQl1ENCY or ECLIPSES. or the earth, in a lunar eclipse, is called the La... Ecliptic Limit; and her distance from the node in a solar eclipse, when the moon just touches the solar disc, called the Solar Ecliptic Limit. The Limits are respectively the farthest possible distances from the node at which eclipses can take place."· , The LUfI4r Ecliptic Limit is 11 0 25' 40". This is the greatest distance from the moon'l node at which a lunar eclipSe can take place; and in the even" of its happening at such a distance from the node, it must be exceedingly .mall or slight. The SolQ,r Ecliptic Limit is 160 59'. If at the moment at Dew moon her node be more than this distance from the sun, no eclipse can happen. 1'his subject may be elucidated by contemplating the moon as seen in her orbit at A, Fig. 2. As she approaohes her Dode, it is evident that she will overlap or eclipse the lun, as soon as she gets within haIr the sun'. diameter of the ecliptic; as just one-half of the sun is above the ecliptic. That point, therefore, in the moon'. orbit which is only the semi.diameter or both the sun and moon from the eoliptic, is the ecliptic lim';' for r eclipses. . 4. The moon's nodes oonstantly back westw OIl the ecliptic, at the rate of about 1 go per year; 80 .~t she comes to the same node again, as (rom the line mA, Fig. 2, around to A again, in 19 days less than a year; or in 346 days. In just half this time, viz. 178 days, she passes her otber node in the opposite Mide or the ecliptic, as at N. It follows, therefore, that at whatever time of the year we have eclipses at either node, we may be sure that in 173 days afterwards we shall have eclipses at the otber node. And as (or any given year eclipses commonly happen in two opposite months, as January and July, February and August, May and November, these opposite months, whichever they may be, are called fOr that year the Node Montu;' 1;. There cannot be leas than two nor more thao eevea u. ran • Ol_ad. BCLIP8D, Oil OCCULTA.TlOBS 01' TIIB 8TA.IlS. ] 17 eclipses in ODe year. If but two, they will both be of the IIOD; but if seveD, five will be of the Bun and two or the mOOD. The usual number is two IOlar and two lunar. Lesson 89. BCLIP8BS, OR OCCULTA.TIONS OP TIm STDS. The occultation ot a star is caused by the moon'. passing between us and it, and concealing it from our yiew. Though a very simple and common phenomenon, it is, nevertheless, a very interesting one. At New MOOD, especially, the star occulted may be traced to the very border of the moon's eastern limb, when it suddenly goes out. From these stellar occultations, or eclipses the stars, many important conclusions may be drawn. They teach us that the moon is an opaque body, ter. minated by.a real and sharply defined surface, intercepting .light like a solid. . They prove to U8, that at those times when we cannot Me the moon, she really exists, and .pursues her course ; and that when we see her only as a crescent, however , the whole globular bod y ia there, filling up the ent outline, though unseen. For ocoultations take indifferently at the dark and bright, the visible and mVl Ie ouiline, whichever happens to be towards· the. dire on in which the moon is moving; with this only difference, that a star occulted, by the bright limb, if the phenolDenon be watched with a telescope, gives nbtioe, by its graddal approach to the visible edge, when to expect its disappearance; white, if occulted at the dark limb, if the mOOD, at least, be more than a few days old, it is, as it were, extinguished in mid-air, without notice or visible cause for its disappearance, which, 88 it happen. ",.tanta'M0U8ig, and without the slightest previous diminLltion of its light, is always surprising; and, if the star be a large and bright one, even startling from its suddenness. The reappearance of a star, too, wheJ;l the moon has passed over it, takes place, in those cases when the bright aide of the moon is foremost, DOt at the concave or 118 BCLIPSBI 01' JUPITER'8 MOONS. or 'I1tline of the orescent, but at the invisible outline the )omplete circle, aDd is 8Ca~ely le88 surprising (rom ita iuddeDDe&8, than its disappearance in the other case.· Lesson 90. BCLIPSBS OP 1l1PITBJ1'S MOONS. Every planet in the Solar System, whether primary or secondary, casts its shadow in the direction opposite to the $un. But none of the primaries can eclipse each other. In every case, however, where they are attended by satellites, there may be eclipses. Of the number, distance., magnitudu, and motitmB of Jupiter's moons, we have already spoken in Lesson Sl. It remains DOW to consider their eclipsu. From th~ magnitude of Jupiter, and his distance from the sun, it will be seen at once that he must cast a shadow of great dirnensioDs, extending far into space to. wards the orbit of Saturn. But in order fully to under. stand the subject of his eclipses, it ,viII be necessary to take into the .account not only his distance, magnitude, &0., but the near coincidence of his orbit with the ec "tJtic, his equator with his orhit, and the orbits of his moons ith his equator. All these points will be found duly no L)ed under their 8 ppropriate heads in the preceding Ie • Let it be remembered then., 1. That Jupiter casts a broad and long shadow i • the direction opposite the sun. 2. That the centre of this shadow lies in the plane his orbit, which differs only 1!-0 from the plane of the ecliptic. (32.) . 3. That his axis is inclined to his orbit only 80 5', and or course the plane of his equator nearly coincides with that of his orbit. (50.) 4. Three of his moons revolve very nearly in the plane of his equator, and' must consequently pass near .tie centre of his shadow at every revolution. They must., therefore, be totally eclipsed. or • Henchel'. AIIronomy , .. ECLIPSBS OP SATURN AND BBR8CBBL. 119 5. The most distant of his satellites haa an orbit more inclined to the ecliptic, 80 that she IOmetimes but just grazes the border of the shadow in passing, aQd some. times wholly escapes. But these instances are comparatively rare. As a general rule, it may be said that the satellites or Jupiter are totally eclip,ed at Imery rlmolution ; so that by determining the number of revolutions each makes in a month, (81,) and adding them together, we find the number of eclipses in that period of time. They amount to about forty. 6. FroIn the marne,. of his satellites (Lesson 81) we infer that they must pass his shadow where its diameter must be nearly as great as that of Jupiter; hence the eclipses are usually total, an. last for some time. 7. The ,hadolD. of the satellites, being much longer than those of our moon, on account of their greater distance Crom the sun, and the neamess of the satellites to Jupiter, are cast upon Aim at every revolution. They may be seen with good telescopes" like small round ink .pot8~' traversing his disc. ' 8. The entrance of Jupiter's moons into his shadow is called their immerBion; and their egress therefrom their emer,· • Tables have been constructed showing the pr•• ei8e ',' 11&8 when these shall take place, for a given longi. tud n the earth, as, for instance, Greenwioh Observatory whioh tables are employed, in connection with a cA~ fer or accurate timepiece, for determining terrestrial ongitude. • LeS80191 • ECLIPSES OP SATURN AND HERSCHBI.. or the satellites of these two planets, too little is known to admit oC any very positive statements in respect to their eclipses. Indeed very little is said upon this subject, even by the ablest practical astronomers. Of Saturn it is remarked by Dr. Herschel, that owing to the obliquity of his rings, and of the orbits of hiS satellites to the ecliptic, -they Buffer no eolipses, the interior ones excepted, uatil • 120 NATt7KB .llfD CAUSES or TIDBS. Dear the time when the rings.are seen edgeuMe. (See Leason 66, and Map.) or the eclipses of Hersohel's mOODS, nothing whatever Is known by observation, and very little by theory, 88 deduced from their distances, inclination orbits, &0. . . or CHAPTER V. PHILOSOPHY OF THE TIDES. Lesson 9~. I KATURE AND CAUSES OP TIDBS. (Map 14.) THB alternate rising and falling of the waters 0 r the ocean are called Tides. The rising of the waters is called Flood tide, and their falling Ebb tide. There are two flood and two ebb tides every day. The caUBe of the tides is the attraction of the SUD and moon upon the earth and the waters surrounding i Fig. 1 represents the earth surrounded by wate ~D a Itate or reet, or as it would be were it .no~ acted up ~ by the sun and mOOD • . Fig. 2 shows the moop at a distance above the !a~h, and attracting the waters of the ocean 80 as to p. uce a high tide at B. But as the mOOD makes her apparent westward revolution around the earth but t.)nce a day, the simple raising of a flood tide on the side of the earth towards the moon,. would give us but one flood and one ebb tide in twenty.four hours; whereas it is known that we have two of each. Fig. 8, therefore, is a more oorreot representation of the tide. wave, as it actually exists, except that its height, 88 compared with the magnitude of the earth, is vastly too great. It is designedly exaggerated, to illultrate the principle under consideration. While the moon at A produoea a big~ tide at B, we see a high tide at-,C, on the NATURE AND CAUSES ~ . ,. or .. 121 opposite side of the earth. Of course it is low tide, at this time, at D and E; and as these four tides, viz. two high and two low, traverse the globe from east to lVest every day, it accounts for both the ,rising and falling or the tides every twelve bourse But the most difficult point remains yet to be elucidated. "The tides," says ,Dr. Herschel, "are a subject on which many persons find a strange difficulty of conception. That the moon, by. her attraction, should heap up the waters . of the ocean under her, seems to most pel'8ODS very nat.. ural. That the same cause should, at the same time, heap them up on the opposite side of the earth, [8S at C, Fig. 3,] seems to many palpably absurd. Yet nothi~g i. more true, nor indeed more evident, when we consider that it is not by her !Doole attraction, but by the differencu of her attractions at the two surfaces and at the centre, that the waters are raised."~ , The law of gravitatio~ (17) is the same which prevails in the diffusion of light, (12,) namely, that its force ia .fJer8ely Q,8 the 8quare8 of the diatancea; or, in other words, as the squar~ of the distance is diminished, the force of attraction is increased, and ",ice 'Der8d. Let this rul~ be applied to the earth and moon, Fig. 3. t In the first place, nothing can be more evident thaa tJ»' the tide-water at B is the whole diameter of the ea:. ,or 8,000 miles near.er the mOOD at A than tbe wai r8 of the opposite side of the earth at C. They must also be 4,000 miles nearer than the centre of the earth, or the parts between D and E; while these parts, turn, are· 4,000 miles nearer than the waters at C. 2. Now as the force of ~e moon's attraction depends upon her distance, it must follow, in the second place, that the different parts of the eartb will be uneq1J.ally attrfU!ted. B will be attracted more than D E, and D E more than C • . 8. This unequal attraction of the different parts of the earth's surface will tend to 8eparate these parts. As B is more strongly attracted than the body of the earth, it in .. TIDES. • Treatille, 315. 11 122 LAGGING OF TIlE TmE, ETC. will be drawn farther towards the mOOD, 80 as to produce a high tide on that side of the earth. The body, or solid parts of the earth, being nearer to the moon than the waters at C, will also recede from them towards the moon, causing the waters of the other side of the earth to tend (rom D E towards C, and raising a high tide at that point. 4. This perturbation, or swinging of the earth one way and the other, in her orbit, is assumed to be a CODstant result of the moon's attraction. Though the earth never deviates from her course more than the amount o( her diameter, yet this is considered sufficient to account (or the high tides opposite the mOOD, when in conjunctiOD with the SUD, upon the principles already explained. For a Dew theory of tides, see Lesson 94. Lesson 93. LA.GGING OF THE TIDE-EXCURSIONS IK LATITtTDB. (Map 14.) 1. The vertex, or highest point of the tide. wave, is generally about three hours behind the moon in her sage westward. This is illustrated at Fig. 4, wher moon \ is seen on the meridian at A,. and the tide. hanging back to the east, with its vertex at B. tide will be rising at C when the moon passes the ·d. ian; and will continue to rise for three hours afterwards, when it will reach its highest point, and begin to ebb again. • The cave of this delay of the tide. wave is a want of time {or the waters of the ocean to yield to the impulse given to them by the moon's attraction. Besides, as the moon continues to act upon the waters east of her meridian, for some time after she has passed over them, it is natural that they should still oontinue to rise. 2. Not oDly does the tide lag behind the moon, but the moon lags behind her hour, 80 to speak, or rises later and later every night, as she advances eastward in let' orbit; so that high or low water is about fifty minutel I ·1 IPKllfG AND NBAP TIDBI. 123 Jater every day, in reaohing any particular meridian, than 00 the day preceding. 8. The position of the moon in regard to the equinocUo,l has also its effect in modifying the tides. This is illustrated at Fig. 5, where the moon is seen at A, Bout" of the equinoctial, and the vertex of the tide. wa ve at B, on the Tropic of Capricorn. Of coul"8e the vertex of the opposite wave would be at E, in the nortkem hemisphere. Were the moon at C, or north of the equator, the vertices of the wave would be shifted from Band E to D and F. It is in this way that the declinatiOA of the sun and moon ( 47) materially affects the tides in any particular latitude. As the vertex of the tide-,,·ave tends to place itself verti. cally uad~r the luminary which produces it, when this vertical Qhanges jts poin~ of incidence on the surface, the tide.wave must tend·to shift accordingly; and thus, by monthly and annual periods, must tend to increase and diminish alternately the ptiRcipal tides. The period the moon's nodes is thus introduced into this subject; her excursions in declination in -one part of that period being 290, and in another only 17G ,:on either side of the&. equator.· . is on this aocount, that in high latitudes 'e~ery al. tel ate tide is higher than the intermediate ones,.. the e~ ing tides in summer exceeding the morning tides, ali·, tbe morning tides in winter exoeeding those of the I or e'Yelling. Lesson 94. 8PB.DfG Am)" NEAP TIDES. (Map 14.) I or 1. We have hitherto spoken chiefly the" moon as in. strumental in the production of the tides. But though ahe is the priMipal, she is not the only cause. The mass .of the SUD is seventy millions times greater th an that of the moon, (70,) but in consequenoe of his great di8tanu, or • Benchel'. Treatile, 317, 318. 124 IPalKQ AND NLlP TIDES. his influenoe upon the earth in the productioD of tides i. only about one.third as great as that of the moon. Still it is amply sufficient to produce a perceptible tide-wave of self, independently of the aid of the moon. Now as the solar and lunar influences are to each other as one to tlree, it is evident that when the two forces are combined they will p'roduce tides one.third hig1aer than usual; and when they counteract each other, the lunar tide-wave will prevail, but will be one·third lower than usual. These extraordinary variations are called the Spring and Neap tides. There are two of each every month. The .pring, or highest tides, occur at the ayzygie8, or at new and full mOOD, and the neap tides at her quadratures. A, B, C, F, Fig. 6, are intended to illustrate theae phenomena. At A, the moon is seen in eonjuftction. It is now new moon, and the sun and moon act together upon the waters of the ocean, producing a Spring'ti.tk. The map shows the tide.wave as considerably higher than at F or B. 2. At B, the moon has passed to hel' fir" quarur, so that her attraction is in a direction at ri$ht angles with that of the sun. But as she exerts three1°urt.1uJ of all the attracti ve force of the sun and moon both, she succ de in producing a lunar tide in apiJe of the BUn, thoug . IJUbtraots one.third from what would otherwise be elevation. On these principles we account for the i'- ~8. • . 8. At C, the sun and m90n are seen in oppoaition, and the earth exhibits another qring tide. But here it is evi. dent that the tide.wave opposite toeaoh lumintry respeotiv~ly, cannot be materially augmented by the perturbations' of the body of the earth, as illustrated at Fig. 8, and explained at the beginning of this chapter: (or as the sun and moon act in direct opposition to each other, they tend to keep the earth from swinging towards either. But as the moon exerts three times the force of the BUD u~ the earth, she will attract the earth towards her, in spite of the sun; 80 that she will thus contribute to the pNd uction of the tide-wave 00 the side of the earth towarda C. On the hemi2tphere t.orDard. the moon, she must raiae 8PJlUtG AltD NEAP TIDK!. 125 or her own tide, and that, too, with the whole (orce the 8un's attraction acting against ber. How, then, is the spring tide produced at this time on the side of the earth opposite the SUD 7 And yet such is the fact. Here is a point which it must be acknowledged is not aatisfactorilyexplained by the prevailing theory of tides. When the sun and moon are in oppoBititm, they must necessarily dimlniaA that perturbation of the earth, which is assumed to be the cause of spring tides, and as the cause is reduced, the effect also should be reduced. Ac. co~ding to this theory, therefore, we ought to have a ""1' instead of a ayring tide, w ben the SUD and mOOD are in opposition. The earth cannot swing in two opposite di. rections at the same time. Even Prof. O~msted, whose abilities as an astronomer and mathematician are univer. sally acknowledged, seems to be at a loss here. He says :-" At the time of new moon, the sun and moon both beiD~ on the same side of the earth, [u represented at A and n,l and .acting upon it in the same line, their actions conspire, and the sun may be considered 88 add.. ing so much to the force of the mOOD. We have already exp ·oed how the moon contributi\8 to raise a tide on the OPI ite side of the earth. But the sun, as well as the . mo ,raises its own tide-wave, which, at new mOOD, co. inc es with the lunar wave. At full moon, also, the two ·lumiDari~ conspire in the same way to raise the tide; for we must recolleot, that eaoh body contribute. to r~ise the tide on the opposite side of the earth, a8 well as OD the siJie nearest to it. At both tbe conjunctions and oppositions, therefore, that is, at ~he ,yzygie8, we have ~DU8ually high tides."* . Here it will be seen that the learned author speak. of the fact of spring tide at full moon, and refers to t)ae general prinoiples upon whioh we aocount for spring tide at netD moon; but 10tD the sun and mOOD, acting in oppo.. can ·produce spring tides, remaiDs yet to be explained. 4. At F, we see the moon in the neighborhood of her .u.um, • IntrocluotioD to AItroaomy. 168. 11* 11 .. .. 126 PROFESSOR DAVIKS' THEORY. .l4at quarter, and the earth exhibiting the neap tidu again. We have thus passed through with one lunation, in which we have at A· and a, tlDO qring tide., and a1 Band F t'IDO neap tides. The spring tides are not at their height at the m0ment of the syzygies, but about thirty.six hours atiel\. wards. PROFESSOR DA. VIES' THEORY. Since the foregoing was in type, the author accidentally met with Prof. Davies, formerly of West Point, woo in view of the exceptions we had taken to the prevailing philosophy, on the preceding page, submitted the follow. 109 theory. So far as we can discover, it is a philosophical one, and it is certainly more satisfactory u pan 1001e points than the prevailing doctrine, which we had previously ventured to call in q~estion. In the correctDess of his theory, Prof. D. expresses entire confidence; and by his consent it is here inse_rted for the benefit ol the reader. The principle upon which he accounts for the tidee. is that of Aydt08tatic pressure. When Ouids of di . ent apecific gra vity are mingled together, the hea vie ill displace the lighter, and cause them to rise to the suO If the waters of the ocean were not acted upon b IUD or moon, their specific gra vity would be the arne all over the world;· and they would consequently balanoe each other, producing equilibrium, as represented at Fig. 1. But the sun and moon do attract the waters of the ocean, and destroy their equilibrium. Take the earth and mooq 88 represented at Fig. 3. While the moon is at A, the tendency of ber attraction is to diminish the 8peoifio gravity or weight of the waters at B, as she over. comes a portion of the earth's gravitating force; so that these waters become lighter than they are wont to be. At the same time the moon acts upon the waters at D E with a slightly diminished force; but the tendency at these points is in a Aoriumtal direction, or from D E towards A, and not away from the earth's centre. ()t course, then, the specifio gravity the water is DOl or OTua IKBQ17ALITIBS OF TBB TIDES. 127 ZU.ened at D and E, but rather increaeci. But as the waters. at B are rendered lighter by the moon's attraction, the waters at D E, having retained their uaua) weight, at least, will displace the former, thus causing the waters to ran at D and E, and rise at Band C. In a word, the difference in the direction·of the moon's attraction. at Band D E, as respects a perpendicular to the earth's centre, makes a difference in the tDeigA' of the waters at these two points; and the waters at DE', being 1&eamut, sink down till the lighter waters at Band C are increased enough in tIuantity to balance them; or till eq uili bri um is prod uced. . , This theory applies as well to spring tides at rull moon as to any other tides; and besides, it requires DO sensible perturbations of the earth as' the result of the moon's attraction. It is, therefore, preferable to the com. mon theory laid down by authors, and is commended to the student as decidedly the beat method of accounting for the production of Tides. Lesson 93. OO:UBR .( ~NEQUALITIES OF TUB TIDBS. (Map 14.) 1. The tides vary in height, according to the dJltaneu the earth and moon at the time when they occur. Take, ror example, the spring tides at New Moon. If the earth. is at her aphelion distance (rom the 8un, and the moon in apogee, as we see represented at A, Fig. 6, the attraction of both the sun and moon will be less thaD their average amount, 80 that there will be but a moderate spring tide; but if the moon is in perig"!3e, and tbe earth at' ber perihelion distance, as seen at D, both the sun and ~oon, being at their nearest points to the earth, and in conjunction, \vill exert their full attractive inftu. ence upon the earth; and the spring tide will be unu.ually high, as shown on the map. 2. AtE the earth is near her perihelion, and tbe mOOD in opposition and in apogee. In such a case the or I .. ] 28 OTDB. INBQUA.LITIES OF TBB TmBS• • un has his gr«J,#,eBt· agency in produoing the tidel and the moon her l«ut. This will tend to equa:lize their fOrces, .and only an ordinary spring tide will be pro. duced. 3. The IMigh,t of the tide-wave in different parts of the . world is exceedingly' various, owing to its being crowded into narrow channels in lOme in8tances, and to various other local causes. In open seas the spring tides aTe about eleven, and the Deap tides about seven feet. At London the spring tides rise to the height of nineteen feet; at the mouth of the Indus, thirty (eet; in the river Sev. em, England, forty feet; at St. Maloes~ in France, fortyfive feet; and at Cumberland, Bay of Fundy, seventy-one feet. This last is the highest tide in the world, and is caused by the meeting of the great northern and southern tide-waves of the Atlantio, which here come together in opposite directions. . The height of tides on dHFerent portiODS of the westem continent has been given as follows: Cumberland, Bay of Fundy,. • • • • Boston, New Haven, • • • New York,. • • • Charleston, s. C~, • • • • • • • • 71 feet. • 11 " • 8 • 0" • 6" eel ' This table seems to accord well with the theory JUst named, in regard to the cau, of the excessively high tides in the Bay of Fundy. 4. The lagging of the tide. . wave behind the moon (93) is greatly mOdified by local causes. Though the tides are usually highest about three hours after the moon has passed the meridian, it is often retarded by shoals and channels, an61 by Btriking against oapes and headlands, so that, as exceptions to the general rule, high tides bappen at all distances of the moon from the meridian. 5. Lakes and inland seas have no perceptible tides, in consequence of their incoDsiderable magnitude, as com· pared with the waters of the ocean. 6. Dr. Herschel Qbserves that the actiOIl of the Bua APSIDBI OF TBB MOON'S OIlBIT. 129 in and moon produoes tidu in ,he atmoBpAere, as well as the water; and that delicate observations have rendered them sensible and measurable. The pupil will find a remark "concerning titU. OR the IUtI, in Chapter VII., where the various theories of the solar spots are oo~8id ered. Lesson 00. XOTION OP THE APSIDBS OF THE IIOON'S ORBIT. (Map 14.) At th.e close of Lesson 73, we promised in this chapter to' speak of the motion or revolution of the moon's apaide,. The ap.ide. of the moon's orbit are her perihelion and aphelion points in her orbit; and the line of the apsidel is a line drawn through those points, as shown in Fig. 6, wherever the moon's orbit is represented. At A this lin~ is marked M A. N ow the motion of the apaide8 is the revolution of these points around the ecliptic from west to east. The map shows this revolution as we trace the mOOD around from in which pll.ce the line of the apsides, or the rna· A jor ;. xis of the ellipse, is at right angles with itself, as aho· n at A. The apsides of the moon's orbit make a complete revolution in about nine y~ars. In four and a half yean the line A M will shift ends, 80 that the perihelion point M will be towards the sun; and in four and a half years more it will shift ends again, so that the moon will reach her perigee again at M, or in the same part of the heav. ens. In this wa.y the apsides constantly advance east. ward, till, at the end of nine yeara, they finish a complete revolution. It will not be supposed, after what we have said above, that the apsides shift ends IUddtmly, or all at once. This is not the case. Their motion is gradual and uniform, as Gown on the map. As already stated in the ohapter on Eolipses, the mo. tion of the moon's apsides must always be taken into the. . 1F, • 130 DBSCBII'TION OF COK.TAKT BODIBS. account in predicting their ocourrence,' as well u in the explanation or the tides. CHAPTER VI. OF COMETS. Lesson 97. GENBRAL DESCRIPTION or COKETAltY BODIBS. (Map 10.) 1. CollETS are the most singular class of bodies belong ing to the Solar System. They derive their name frolla the Greek word coma, which signifies bearded or kairy. 2. A comet usually consists of three ~arts-the Nuclew, the En'Oelope, and the Tail. . The Nucleu is what may be called the body or lead of the comet, as seen at N, on the map. The En'Delope is the nebulous or hairy covering that surrounds the nuoleus. It may be:ren around the nuclei of several of the specimens on the lap, and especially that of 1585. The Tail of a comet· an expansion or elongation of the envelope. . 3. Some 90mets have no percephhle flUCltUl, their entire structure being. like that of a thin vapory cloud, passinI' rapidly through the· heavens. 4. Many comets have simply the envelope, 'fIJiiIumt tailor elongation. Such were those that appeared in 1585 and 1763, the former of w~ich will be found on the map. 5. Cassini describes the comet of 1682 as being f~ round and QJl bright QJl JU'Pit.er, untAout eve. an en"elupe. But these are very rare exceptions to the general charaoter of cometary bodies. 6. The tails of comets usually lie in a direction 0f1P0me to tAe BUn; 80 that from perihelion to aphelion they precetk their nuclei or heads j or in other worda, cometa .ft, DBSCRIPTION OF COMETA.RY BODIES. 131 .eem, after having passed their perihelion, to back out of the Solar System. See Map 2 . .7. The comet of 1823 is said to have had two taila, ODe of which extended to1Dards the sun. This comet may be eeen on the map, with a portion of its orbit. The sun is supposed to be on the left, and the comet passing down towards its perihelion., Its nucleus and envelope are distinctly represented. , 8. The tails of comets are usually curved more or less, being concave towards the region from whence they come. This is well shown in the comets of 1811, 1823, and 1680. That of'16~9 is said to have been curved like a Turkish .bra, as shown on the map. . The C4IUe of tbis curvature of the tails of comets is supposed to be a very rare ethereal substance, which per. vades space, and offers a slight resistance to their progress. or course it must be almost infinitely attenuated, as the comets themselves are a mere vapor, which .'could make no progress through the spaces of the heavens 'were they not yery ,nearly a vaouum., They could-no more pass a medium as dense as our atmosphere, than an ordinary cloud could pass, through the wate~s of the sea. . 9. ~mets ~av, been known to exhibit 8f.."eral tai14 at tbe' same time. That of 1744, represented on the map, had no less than ail: taila spread out in the heavens like an enormOus fan., .' . 10 .. The tails . .of comets 'do· not continue of the aame Uniform length. They incretUe both in length and breadth as they approach the SUD, and contract as they recede from ))im, until they 9ften nearly disappear before the comet, gets out of sight. ' 11. Instances have ocourred in which' tails of comets have been BUddenly 6lpanded or elo-ngau,d to, a great distance. This is said to have been the case with t,be 'great comet of 1811. . 12. or the p1&yaical nature of comets little is known. That they are·.in general ve~y light and "apo/', bodies ia evident (rom the fact that stars have sometimes been seen even through their deri~e8t portions, and are generall) visible through their tails; and from th~ little attractivo I 132 MA.GNITUDES, BTC., OF COMETS. influence they exert upon the planets in causing perturbs. tions. While Jupiter and Saturn often retard and delay comets for months in their periodio rev 01 utions, comets have not power in turn to ktuten the time of the planet. for a single hour; showing conolusively that the relative masses of the comets and planets are almost infinitely disproportionate. Such is the extreme lightness or tenuity or cometary bodies, that in all probability the entire mass of the largest of them, if condensed to a solid substance, would not amount to more than a few hundred pounds. Sir Isaac Newton was of opinion that if the tail of the largest comet was compressed within the spaoe of a cubic inch, it would not then be as dense as atmospheric air! The comet of 1770 got entangled, by attraction, among the moons of Jupiter, on its way to the sun, and remained near them for four montha; yet it did not sensibly affect ] upiter or his mooDS. In this way the orbit8 of comelS ar.e often entirely changed. That they are in themselves upaque bodie" and aline only by reflectitm, is evident from their sometimes exhibiting distinot pkaae,; from their in. creased brightness as they approach the sun; and from the known difference in the properties. of direot and re· flected light. The idea that they are: in reality, "fiery bodies," is unquestionably erroneous. Lesson 9S. IUGNITtrDBS, VBLOCITJBS, .A.ND TBftlPBRA.Tl11lB 01' COIIBTS. (Map 10.) 1. The REA.DS or ftueld or comets are comparalifJel, Mall. The following table shows the estimated diameter in five different instances. The comet ol1778, diameter of head 33 mil81. " 1805, " 36" " 1799, " 482" " 1807, ., 666" .. 1811, " 428" • •CHfITU'DBI, BTC., OF COQTS. or 133 or 2. The TAILS comets are often enormoul length and magnitude. That of 871 before Christ was 600 long, covering one third of the visible heavens. In 1618, a comet appeareo whioh was 1040 in length. Its tail had Dot all risen when its head reached the middle of the heavena. That of 1680 (see map) had a tail 700 long, 80 that though its head let soon after sundown, its tail eontinued visible all night. The following table will show the length of the tail. 9( some of the most remarkable oomets, both in degreea ud in miles. They will be characterized only by the year when th~y appeared. B. c. 371, A. D. 1456, 600 60 1618, 1680, 1689, 1744, 1'769, 1811, 1843, 104 " " " " " " " 70 68 30 90 23 60 · • -· - • • • 140,000,000 miles. 70,000,000 " 65,000,000 " 123,000,000 " 100,000,000 " 85,000,000 " 48,00(},000 ". . 182,000,000 " 130,000,000 " As these Mtimates are the angles under which the cornela were viewed fr(1fA tAe ellrti, the length of their tails in miles would not be proportional to the angle merely, as their diataf&Cu must. also be taken into the acoount. .~ the comet of ItJ43, 'with all angular length of only 600 was longer in fact by 65,000,000 miles than:~be comet or 1618, with aD angular lellgth of 1040 • At the time of measurement the latter was much nearer to the earth than the former· when his dimetl8ions were estimated. The pupil should look up the comets named in the above table, 80 far as laid down on the map. 3. The VELOCITY with which comets often lDOye, i. truly wonderful. Their motions are accelerated &8 they approach, and retarded as they recede from the sun ;. 10 that their velocity is greatest while passing' their perihelions. The comet of 1472 described an arc or the heavens of 1200 in extent in a single day! That or . 12 -- 134 PBRIODS, BTC., OP COJOTS. or 1680 moved, when Dear its perihelion, at the rate 1,000,000 miles per hour. 4. The TEMPERA-TUBE of some comets, when nearest the sun, must be very great. That of 1680 came within 180,000 miles of the Bun's surface, and muat have re. ceived 28,000 times the light and heat which the earth receives trom the sun-a heat more than 2,000 times greater than that of red.hot iron! What ~ub8taDce can a comet be composed of to endure the exfremes of heat and cold to which it is subject 1 Some have supposed that their tails were caused by the sun's light and heat rarefying and driving back the vapory substance composing the envelope. Lesson 99. PBllIODS, DISTANCBS, AND NUMBER OF COMBTS. (Map 15.) 1. The PERIODS of but few comets are known. That of 1818, called" Encke'a Comet," has a period of only 3l years. Biela'8 Comet has a period of 6t years. That 01 1682 (then first noticed with care, and identified as the same that had appeared in 14:5(J, 1531, and 1607) has a period of about 76 years. It is called Halley" Comet, after Dr. Halley, who determined its periodic time. The great comet of 1680 has a periodic time of 57() years, 80 that its next return to our system will' be in the year 2,250. Many are supposed to have periods of thou. sands of years, and some have their orbits so modified by the attraction of the planets as to pass off in parabolic curves, (0 return to our system no more. Prof. Nichol is of opinion that the greater Dumber visit our system but once, and then tty off in nearly straight lines till they pass the centre of ·attraction between the Solar System and the Fixed Stars, and' go to revol va around other .suns in the far distant heavens.· Sir John Herschel expresses the same sentiment. . I t .- Solar System, p. 135. t Treatise, American Rd. p.. 189• • JtBIlODS, BTO., O. OOUTS. 135 2. The DISTANCBS to which those comets that return must go, to be 80 long absent, must be very great. Still their bounds are set by the great law of attraction, . for were they to pass the point "where gravitation turns the other way," they would never return. But some, at least, do return, after their" long travel of a thousand years." What a sublime conception this affords us of the almost infinite space between the Solar System and the Fixed Stars! The perihelion distances of the various comets that have appeared, and whose elements have been estimated by astronomers, are also exceedingly variable. While lOme pa~ very near the sun, others are at an immense distance from him, even at their periheli~n. Of 137 that have been particularly noticed, 30 paased between the Sun and the orbit of Mercury j 44 between the orbits of Mercury and Venus; 34t ' " " " Venus and the Earth; 23" 6 " 8. The " ." " " the Earth aDd Mars; ~ars and Jupiter. of comets belonging to, or that visit,. the Solar System is very great. Some have estimated them at several millions. When we consider that most comets are seen only through te~escope&-an instrument of comparatively modern date-and that notwithstanding this some 450 are mentioned in ancient annals and chronicles, as having been seen with the naked eye, it is probable that the above opinion is by no means extra vagallt. It is supposed tbat not less than 700 have been seen at different times since the birth of Christ. The paths of only about 140 have been determined. The extreme difficulty of observing comets whose · nearest point is beyond the orbit of Mars, is supposed to account Cor the comparatively small number that have ·been seen without that limit; and the proximate uniform. ity of the distribution of their orbits over the space in. cluded within the orbit of Mars, seems to justify the conclusion, that though seldom detected beyond his path, they are nevertheless equalJy distributed through all the NUMBER 136 DJUCftOlI, ne., OF OOIlBft. of the IOlaJl heayeDl. ReaSODiBg upon this hypothesis, Prof. Arago conclude8 that there are- probably . . . fIIilliDu o( comets that belong to or visit the Solar 8p8ce8 Sy8tem.- Le880D 100. DUlBCTIO!l, ORBITS, A.ND !lA-TUllB 0' COJIBTS. (Map 15.) 1. The DlllBCTION ot- comets is 88 variable as their torms or magnitudes. They enter the Solar System from all points of the heavens. Some seem to come up from the immeasurable depths below the ecliptic, and, having doubled "heaven's mighty cape," again plunge downward with their fiery traiDs, and are lost for ages in the eth~real void. Others appear to ~me down from the zenith of the universe, and having doubled their perihelion, reascend rar above all human vision. Others again are dashing through the Solar System, in all possible directions, apparently without any prescribed path, or any guide to direct them in their eccentric wanderings. Instead of revol viog uniformly from east to west, like the planets, their motions are direct, retrograde, and in every conceivable direction. ~. It is remarked by a late writer,t that the average ifaclinaticn&8 of all the planes in which the comets now on record have been found to move, is about 90°. This he regards as a wonderful instance of the goodness of Providence, in causing their motions to be performed in a manDer least likely to come in contact with the earth and the other planets. 8. The (orm or the comets' orbits is generally that o( an ellipse greatly flattened or'elongated. The sun being near one end of the ellipse, and the planets comparatively in his immediate neighborhood, the comets are in the vicinity of the sun and planets but for a. short time, and • Arago and Lardner', Astronomy, p. 70. t Prot Keadall of Philadelphia. • -~--T""""- DI1lBCTION, BTC., ! • _. or COMBTI. 137 then hasten outward again, beyond the limits of human vision, even with the aid of the best .-telescopes, to be gone even for centuries! 4. Comets were fonnerly regarded as harbin~ers famine, pestilence, war, aod other dire calamiues. ID one or two instances they have exoited seriou8 appre. hension that the day of judgment was at hand; and that they were the appointed meesengers of Divine wrath, basting apace to bum up the world. It may be well, therefore, to devote a paragraph to the question, Are t;omeu dangerow in the Solar SyBtem 1 That they are not, will be evident when we consider, First, that there is scarcely the remotest probability of a collUian between the earth aod a comet. It has been determined, upon mathematical principles, and after the most extended and laborious calculation, that of 281,000,000 of chances there is only one unfavorable, or that can prod uce a collision between the two bodiefJ. The risk, therefore, to which the earth is exposed of being .t~uc" by a oomet, is lik~ the chance one would have in a lottery, where there were ~~,O()O,OOO black balls and but one white one; and where the white ball 'must be produoed at the first drawing to secure a prize. In the second place, if a oomet were to come in direct collision with the earth, it is not probable that it would be able even to penetrate our atmosphere; much less to duh the world in pieces. Prof. Olmsted remarks, that in suoh an event not a particle of the oomet would reach the earth-that the portions encountered by her would be arrested by the atQlosphere, and probably ioftamed; and that they would perhaps exhibit on a more magnificent scale than was ever before observed, tbe phenomena shooting sters, or meteoric showers.· The idea, tber~ {ore, that comets are dangerous :visitants to our system more support from superstition than from reason or 1C1ence. I cannot better conol ude this chapter than in the language of the lamented Burritt: "What regioD. theae or or ha:s • 138 ••• A.O UIPBOTIKG 'I'D lVII, BTC. bodi. visit, when they pus beyond the limits or our Yiew; upon what errand. they ~me, when they again revisit the central parts or our system; what is the difference between their ·physical constitution and that or the .un and planeta; and what important ends they are destined to accomplish in the economy or the uni. Yerae, are inquirie. which naturally arise in the mind, but which lurpa.- the limited powers of the human ua clentaading at present to determine." CHAPTER VII. OF THE SUN. Le8H. 101. a.naA.L :aBMA.:aXS RBSPBCTIlfG TBB BUX-ITS JUaNI• . NDB, BTO. (Map 4.) ALTHOUGH it has been found neceasary to give mal1Y in. terestios facts respeoting the 8un, in the precediDg lea.. tona, it is thought important to repeat them· here, with others, in a more Bystematic order; and with opportunity tor deeoriptioD8 and explanations more in detail. Of all the celestial objects with which we are acquainted, nODe make 80 strong and universal an impression upon our globe as does the Su. He is the great oentre of the Solar 8yste~ vast and fiery orb, kindled by the AI. mighty on the mom or oreatioD, to oheer the dark aby88, and to pour his radiance upon 8urrounding worlds. Com. pared with him, all the 101ar bodies are of inconsiderable dimensioD8 j and without him, they are wrapped in the pall of intenninable night. . The aun is 886,000 mileS in diameter. Wen a tunnel opened through hi. centre, BDd a railway laid down, it would require,· at the rate of thirty mil. per hour, nearl., -----. ...---.--~ .....-~.----......-- - --ROTS OlC TIIB BUK-Tlmla XV.DIl. ] 39 three and a haIr years (or a train of cars to paas through it. To traverse the whole circumference of the SUD, at the same speed,. would require nearly elev~D years. His diameter is 112 times that· of the earth, and his rna. 1,4:00,000 times as great. He is 500 times lar~er thaD all the rest of the Solar System put togeth~ The mean diameter of the moon's orbit is 480,000 mlles; and yet were the sun to take the place of the earth, be would fill the entire orbit of the mOOD, and extend more than 200,000 miles beyond it.on every side. The. form of the SUD is that of a 8pAeroid; his equatorial tieing somewhat greate.r thaD his polar diameter. The map referred to exhibits the relative diameters of the lun and planets. I • Lesson IO~. SPOTS ON THE SUN-JfHBIK NUXBB•• (Map 4.)' By the aid of telescopes a variety qol6 are often discovered upon the sun's disc. Their . . .6er is exoeedingly variable at different times. From )611 to 1629, a period of 18 years, the sun was Dever found olear of spots, exc~pt for a few days in December, 1624. At other times twenty or thh1Y were frequently seen at once; aa.d at one period, in 1825, upwards of fifty were to be seen. Prof. Olmsted states that over one huodred are sometimes visible. From 1650 to 1670, a period of 20 yeare, ecarcely any spots were visible; aod for eight years, from 1676 to 168', no spOts whatever were to be seen. For the last 46 years, a greater or less Dumber of 8pots have . n visible every year. For several days, during the latter part of September, 1846~ we could count six .. teen of these spots which were distinctly visible, aDd moat .of them well defined; but OD the 7th of .October follow .. ing, only six small .pots were visible, though the orne telescope was used, and oirou~tanoes were equally yorable. . or r.. "~ I ! · LeSSOR 103. KA.T11:aB OF THE SOLA:a SPOTS. (Map C'" 4.) . or The appearance of the solar spots is that a dark .11lurrounded by a border le88 deeply shaded, called a peRllfMTa. They are both well represented on the map. When seen through · a telescope, the sun presents the appearance of a Tut globe, wrapped in an ocean of flame, with the spots, like iucombustible islands, floating in the fiery aby88~ The principal facts by which we are to judge of their nature and eGU8U, are the following: 1. The Bun is often entirely de8tUKte of spots. 2. When they are to be seen, the same spots do Dot regularly reappear on the east; and pass around, with every successive revolution, to the west. 3. They are exceedingly variable as to .umber and flUJ6"itude • ,. They have been known to b,.eak it116 piecu, and die vide, and even finally to di,appear altogether in a very Ilion time. 1\. They sometimes break out again in the same places ; and Dew onel often break out where none were per. ceptible before. 6. When they disappear, the central dark lpot alwaYI contracts into a point, and vanishes before tbe penumbra or border disappears. 7. In the neighborhOod of the large spots, tbe surface the IUD is covered with strongly-marked streak. or arms, more luminous than the rest, called facuI., among which the spots often break out. The (lark spots are IOmetimes called flUlCUke. 8. The spots are all found within 800 or the 8un's equator, or in a zone of 600 in width. . 9. In a aeries of experimentl conducted by Prof. HeDry, of Princeton, by means .of a thermo-electrical or j I I I .. ......... - ---_.- 141 WAT1JD 0. 'I'D SOLAIl aI-OTl. apparatus, applied to an image of the 8UIl throwD on a screen from a dark l'OOID, it was found that the spots were perceptibly oolder than the surrounding light sur. face. Concerning theae wonderful spoll a variety of opinions have prevailed and mahy curious theories have been constructed. Lalande, as cited by Herschel, auggUt8 that they are the tops of mountains OD the 8un's surface. laid bare by fluctuation8 in his luminous atmosphere; and that thepenumbr. are the shoaling declivities the mountains, where the luminous ftuid is lees deep. Another gentleman, some astronomioal knowledge, supposes that the tops of the solar mountains are exposed by tidu in the lun'. atmosphere, produced by plaaetary attraction. To the theory of Lalande, Dr. Herachel objects that it is oontradicted by the sharp termination of both the in. temal and external edges of the penumbre; and ad. yances 88 a more probable tbeory, that " they are the dark, or at least comparatively dark, solid body of the sun i~lr, laid bare to our view by those immense fluotuations in the luminous regions of the atmosphere, to which it appeara to be subjeot." Prof. Olmsted Buppana thi. theory by demoDstrating that the spots must be "nearly or quite in contact with the body of the sun." In 1778, Prof. Wilson, of the University of Glasgow, ascertaiDed by a aeries observations that the spots were probably "",an "C4Mtioa. in the luminous' matter the sun;" the nuclei being their bottom, and the umbne their shelving sides.· This conclusion varies but little from that of Dr. Henohel, .ubsequently arri yed or or or or at·t . . • A .aJaable peper apon the aabject 01 the lOlar IpOIII, writteD .., the lameated Ebenezer Poner Muon, may be loud ia Iaia euelJMemoir, by Prot OIJDlted, pap 238. t Nichol', Solar Sy.tem, pp. 121-116. - 142 -~- --". MA.S.ITV». OF TJIIr SOU. SPOTS. LessoD 104. KA.GNITt1DB OF THE SOLAR SPOT& (Map 4.) The f1UJ8ftitude of the solar spots is as variable as their Dumber. Upon this point tbe map will give a correct idea; .a8 it is a pretty accurate representation of the sun's disc as seen by the writer on the 22d ot" September, 1846. In 1199, Dr. Herschel observed a spot nearly 80,000 miles in breadth; and he further states, that .others have been observed 'whose diameter was upwards of 45,000 miles. Dr. Dick observes that he has several times seen spots which were not less that of the sun' 8 diameter, or 22,192 miles across. It is stated, upon good authority, that solar spots have been seen· by the naked eye-a fact, from which Dr. Dick concludes that such spots could not be less thaD 50,000 miles in diameter. The observations of the writer, as above referred to, and represented on the map, would go to confirm this deduction, and to assign a still greater magnitude to some of these curious and interest.ing phenomeDa. , n Le880l 103. eVOLUTION OF THB SUX UPON HIS A.%I8. (Map 4.) The axis of the sun is inclined to tbe ecliptic 71°, or more accur~tely 7 0 20'. This is but a slight deviation from what we may call a perpendioular, 80 that in relation to the earth, he may be oonsidered as standing up ao.d revolviDg with one of his poles resting upon a point just half his diameter below the eoHptic. The proof his revolution is the same as that by which we determine the revolution of the planets, namely, the passage of spots over his disc. He revolves in the same direction in whioh the planets revolve around him, and the time 00.. or -- - - . •, 143 DIRBCTION', BTC., OF IOLA.:a SPOTS. cupied in making a complete sidereal revolution is 25 days 10 hours. But when a particular spot has arrived opposite any partioular atar from which it started, in tbe direction of which the ~arth was 25 days and 10 hourS .before, the earth is found to have advanced some 240, or 1,700,000 miles in her orbit; and the sun must actually tum a little more than ooce round, to appear to make a complete revolution to a lteholder on the earth. His q.nodic revolution consequently requires 27 days 71 hours, or Dear 46 hours more time tha.n his sidereal revolution. Lesson 108. DIaBeTION, MOTIONS, A.ND PRASBS OF '1RB SOLA.R SPOTS. 'Map 4.) , As .the result of the sun's motion uptn his axis, his spots always appear first on his eastern limb, and pass off or disappear.on the west. But though the direction of the spots, as viewed from the earth, is from east to west, it only proves his Dlotion to coineide with that· of the earth, which we call from west to east; as when two spheres revolve in the 8ame direction, the sides towards each other will- appear to move in oppome directions. During one half of the passage of the spots across the 8un's disc, their apparent motion is accelerated; and during thA remainder it is relaraed. This apparent irregularity in the motion of the spots upon the sun's surface, is the necessary re~ult of an equable 1J)0tion upon the surface a. globe or sphere. W hen near the eastern limb, the spots are coming partly toward.. us, and their angular motion is but slight; hut when near the centre, their angular and real motioDs are equal. So, also, as the spots pass on ·to the west, it is their angular motion only that is diminished, while the Illotion of the sun upon his axis is perfectly uniform. The figure of the sun affects Dot only the app~rent ,,~/ocity of the spots, but also their fortU. W hen first seeD on the east they appear narrow and' slender, al .represented OD the left of Fig. 1. As they advance or • 144 PHYSICAL CORI"tH'U110K OF 'I'D au•• westward, they cootinue to wideo tOr eDlarge till they reach the centre, where they appear largeSt, wheD they again begin to contraot, and are constantly diminished till thef disappear. Another result of the revolutioa of. the aOD upon all axis inclined to the ecliptic, and the revolution of the earth around him, is, that when viewed from our moveable observatory, tbe earth, at different .Uona of tbe year, the direction of the spots seems materially to vary. This fact is illuttrated by Fig. 2. In Jiloe we have, 80 to speak, a side view of the sun, his pole being inclined to the lift. course, then, he revolves, his spots will appear to 88Cend in a straight line. In September we have passed around in our orbit, to a poiat opposite the lOuth pole of the SUD, and the .pots 88em to curve upward. In December we have 8DOther side view of the IUD, but we are opposite the point from which we had our first view, and on, the other side of the ecliptio. The reBUlt is, that tbe poles of the SUD are now inclined to the ri8ht; and' the spots, in passing over his diao, incline downward. In March,. we reaoh a point opposite the 80ut" pole of the 8un, and the .pot.s in revolving aeem to ourve downward.. The polar iDclination of tbe 8un, U given in the figure, is greater than it actually is in nature, (see Lesson 49 and Map 8 ;) the present design beiDl merely to illustrate the principle upon which 'we account Cor the peculiar motion Qf the solar spots. or as Lesson 107. PHYSICA.L CONSTITUTION OF TUB St1K. Concerning the physioal aature of the SUD, yery little ,is known. As before said, it appears, wheD 8een through a ~ele800pe; like a globe of fire, in a state of violent com. motion or ebullition. La Place belieyed it to be in a _ate of actual combustion, the spots' being immense cay. ems or craters, cau~d by eruptioDs or exploeioDs elastio ftuids in the interior. ' The most probable opinion 18, that the body. &he BUD or or 1 ~ -,,------...... -_.... "--- ... - -- -" --.- ".-- .. - . ----- ---- ._- PRYSICA.L CONSTITUTION OP TBB SUN. . 145 is opaque, like one of the planets; that it is surrounded hy an atmosphere oC considerable depth; and that the light is sent off from a luminous straJum of clouds, float. ing above or outside the atmosphere. This theory accords best with his density, and with the phenomena of the s0lar spots. \ Of the temperature of the sun's surface, Dr. Herschel thinks that it must exceed that produced in furnaces, or eVt-n by chemical or galvanic processes. By the law relative to tbe diffusion of light (Lesson 12) he shows that a body at the sun's surface must receive 300,000 times the light and heat of our globe; arid adds that a far less quantity of 801ar light is sufficient, when collected in the Cocus of a buming-glass, to dissipate gold and platina into vapor· . The same writer observes that the most vivid flames disappear, and the most intensely ignited solids appear only as black spots on the~disc of the sun, when held between him aDd the eye. From this circumstance he in. fen that however dark the body o( the sun may appear, when seeD through its spots, it may, nevertheless, be in a state of most intense ignition. It does not, however, follow of necessity that it must be so. The contrary is at least physically possible. A perfectly rtjlecti1Je canopy would effectually defend it from the radiation of the lurninous re. gioos above its at~phere, and no heat would be conducted downward through a gaseous medium increasing rapidly in density. The great mystery, however, is to conceive how 80 enormous a conftagratioD (if· such it be) can be kept up (rom age to age. Every discovery in chemical science here leaves us completely at a loss, or rather seems to remove farther from us the prospect of explanation. If conjecture might be hazarded, we should look rather to the knowD possibility of an indefinite generation of beat by friction, or to its excitement by the electric discharge, than to any actual combustion of ponderable fluid, whether IOlid or gaseous, for the origin of the solar radiation. * I • HellCbel'. Treatile on Astronomy. 13 146 TBB ZODIACA.L LIGII'l. Les•• lOS. , THE ZODUCAL LIGHT. The ZodUJcal Liglat is a faint nebulous light, resembling the tail of a comet, or the milky-way, which seems to be reflected from the regions about the lun; and is distinguishable from ordinary twilight. Its form is that or a pyramid or cone, with its base towards the SUD, and inclined slightly to the ecliptic. It seems to surround the 8un on all sides, though at various depths, as it may be seen in the morning preceding the 8UD, as well as in the evening following him; and the bases of the cones where they meet at the 8UD, are much larger than his diameter. The form of this substance surrounding the IUD, and which is sufficiently dense to reflect his light to the earth, seems to be that of a leu; or rather that of a huge wheel, thickest at the centre, and thinned down to an edge at the outer extremities. Its being seen edgewise, Bnd ·only one.half at a time, gives it the appearance of two pyramids with th6ir bases joined at the IUD. Of the fUJture of this singular phenomenon very little is positively known. It was formerly thought to be tbe atmosphere of the IUD. Prof. Nichol says :-Of' this at least we are certain-the Zodiacal Light is a phenomenon precisely similar in kind to the nebulous atmospheres of the distant stars, &0. Sir John Herschel re.. mark~, that it is manifestly of the nature of a thin lenticl.. ''1.rly.formed atmosphe~e, surrounding the SUD, and ex ..e. -ling at least beyond the orbit of Mercury, and even of \ ·nus. He gives the apparent Ilngular distance of its vertex from the SUD, at from 400 to 90 0 ; and the breadth of its base from 8 0 to 300 • It sometimes . extends 500 westward, and 700 ea8t of the aun at the same time. . . In regard to its atmospheric character, Dr. Diok observes, that this opinion now appears extremely dubious; and Prot Olmsted refers to La Place, as ahowing thai • • ... I KOTION OP THB SU'N IN SPA"B. . 147 the BOlar annosphere could never reach 80 far troOI th. SUD 88 this light is seen to extend. Another class of utronomel'8 suppose this light, or rather the substance reflecting this light, to be some of the original matter or which the sun and planets were composed-a thin nebulous substance in a atate of con. densation, and destined either to be consolidated into oer planetary worlds, during .the lapse oC coming agel, or to settle down upon the sun himself as a part of his legitimate substance. This theory will be noticed again when we come to speak of Nebulae and Nebulous Stars, in the ~cond part of this work. Prof. Olmsted supposes the Zodiacal Light to be a nebulou8 body, or a thin vapory mass revolving around the sun; and that the Meteoric SlunDera, which have occurred (or several years, in the month of November, IDay be derived from this body. This is the opinion of Arago, Biot, and others. The best time for observing the Zodiacal Light is on clear evenings, in the months of March and April. It may be seen, however, in October, November, and December, before sunrise; and also in the evening sky. -It is an interesting fact, stated by Prof. Nichol, that this light, or Debulous body, lies in the plane of the sun'. equator. A line drawn through its transverse diameter, or from one apex of the pyramids to the other, would cross the axis of the sun at right angles. This fact would seem to indicate a revol ution of this curious 8U bstance with the sun upon hi, axis. But, 88 already stated, the subject of the Zodiacal Light is in an unsettled state. After considering the various {acta and theories stated, the learner Rlust wait till future observations and discoveries shall furnish some. thing upon this point more definite and satisfaotory. Lesson 109. MOTION OP TO S111'( IN SPA.CK. Although in general terms we speak of the aUD as the ed centre of the Solar System, still the sublime and 148 KOTIOlf OF TD St1K IN SPA.CB. astonishing fact has been ascertained, that the sun, and the whole Solar System, h,afJe aft actual motioR in apace. Indeed the sun may be said to have three distinct motiona. 1. It has a revolution upoo its own axis;once in 25 days.9i hours, as described in Lesson 105. 2. "I t has a periodical motion, in nearly a circular .direction, around the cOin moo centre of all the planetary motions; never deviating from its position by more thaD twice its diameter." From the known laws of gravitation, it is certain that the sun is affected in 8Qme measure by the attraction of the planets, especially when many of them are found on the same side of the ecliptic at the Rrne time; but this would by no means account for 80 great a periodical motioD. 3. It is found to be moving, with all ita retinue worlds, in a vast orbit, around some distant and unknoWll centre. This opinion was first advanced, we think, by Sir William Herschel; .,but the honor of actually determining this interesting fact belongs to Struve, who ascertained Dot only the direction of the sun and Solar System, but also their velocity. The point of tendency is towards the constellation of stars called Hercules, Right Ascension 269°, Declination 35°. See Lessons 47,48. The velocityof the SUD, &c., in space, is estimated at about 28,OOU miles per hour, or nearly 8 miles per second! With this wonderful fact in view, we may no longer consider the su n as fixed and stationary, but rather 8S a vast and luminous planet, sustaining the same relation to some central orb, that the primary planets 8ustain to him, or that the secondaries sustain to their primaries. Nor is it necessary that the stupendous mechanism of nature should be restricted even to these sublime proportions. The sun's central body may also have its orbit, and its centre of attraction and motion, and 80 on, till, as Dr. Dick observes, we come to the great centre of all-to the or THRONE OF GOD. Since the above was written an article has appeared in several European journals, announcing the probable discovery of the sun'8 central orb; the inclination of Ail twbit to the plane oj the ecliptic; and his periodic time! KOTION OF THB SUN , IN SPlCB. 149 As it contains several interesting -calculations, and is otherwise a remaFkable paper, it is here copied for the benefit of the student. THB CBNTRAL SUK. At the close of the meeting of the Royal Irish Acad. emy, on the 14th of December, [1846,] Sir William Hamilton announced that he had just received from ProCessor Midler, of Dorpat, the extraordinary and exciting intelligence of the presumed discovery of a central sun! By an extensive and laborious comparison of the quantities and directions of the proper motions of the stars in various parts of t~e heavens, coQ1bined with indications afforded by the parallaxes hitherto determined, and with the theory of universal gravitation, Professo·r Madler has arrived at the concl uaion that the Pleiades form the central group of our whole astral or sidereal system, including the Milky Way and all the brighter "tars, but exclusive of the more distant nebulm, and of the stars of which those nebulm may be composed. And within this central group itself he Pias been led to fix on the star Alcyone, (otherwise known by the name of • Tauri,) as occupying exactly or nearly the position of the centre of gravity, and as entitled to be called the • . central sun. Assuming Bessel's parallax of the star 61 Cygni, 1.ong since remarkable for its large proper motion, to be cor. recti y determined, Miidler proceeds to form a first approximate estimate of the distance of this central body from the planetary or solar system; and arrives at the (provisional) conclusion, that Alcyone is about thirtyfour million times as far removed from us, or from our own sun, as the latter Iuminary is from us. I t would, therefore, according to this estimation, be at If'ast a million times as distant as the new planet, of which the theorp.ticalor deductive discovery has been so greht and beautiful a triumph of modern astr9nomy, and so striking a confir. mation of the law of Newton. The saRle approximate determination of distance conducts to the result, that the 13· • 150 NBBlJUll TBBORY. , light oC the central slln occupies more than fi,'e centurie. in travelling thence to U8. The enormous orbit which our own sun, with the earth aud the other planets, is thus inferred to be describin~ about that distant centre-not indeed under its influence alone, but by the combined attractions of all the stars which are nearer to it than we are, and which are estimated to amount to more than one hundred and seventeen millions of masses, each equal to the totaJ mass or our own Solar System-is supposed to require upwards eighteen millioru of ,ear. for its complete description, at the rate of about eight geographical miles in every second of time. The plane oC this vast orbit oC the sun is judged to ha va an inclination I()f about eighty.four degrees to the ecliptic, or to the place of the annual orbit oC the earth; and the longitude of the' ascending node of the former orbit on the latter is concluded to be nearly two hundred and thirtyleven degrees. or CHAPTER VIII. MISCELLANEOUS REMARKS UPON THE SOLAR SYSTEM. . • Lesson 110• IfBBULAll TBBOllY 01' THE ORIGIN OF THE SOLAR SYSTKII. IT was the opinion oC La Place, a celebrated French • astronomer, that the entire matter of the Solar System, which is now mostly found in a consolidated state, in the lun and planets, was once a vast nebu1o., or gasepus vapor, extending beyond the orbits of the most distant planets-that in the process of gradual condensation, by attraction, a rotary motion was engendered and imparted to the whole mass-that this motion caused the consolida. ting matter to assume the (orm of variouS' COD cent rio rings, like those of Saturn; and, tinally, that these ringa, collapsing, at their respective distances, and still retaining ~-- ~----------- ---.-- --~-- -...- -- -- -- ------- - -- -- --------- --- NBBUL.&.B. THBOB.Y. 151 their motion, were gathered up into planetl, as they are now found to exist. This opinion is supposed to be favored, not only by the fact of Saturn's revolving ring&, but by the existence of the Zodiaoal Light, Qr a resisting nledium about the sun, (108,) and also by the character of irresol yable or planetary nebullll, hereafter to be de. scribed. . ' On the other hand, the nebular theory is open to many plausi ble, if Dot insurmountable objeotions. 1. It seems to be directly at varianoe with the Mosaio account of the creation of the 8un, moon, and star8. The idea that the sun and all the planets were made up, 110 to speak, out .of the same general mass, not only throws the creation of this matter back indefinitely into etprnity, but it substitutes the general law of attractiOD for the more direct agency of the Almighty. The crea. tion spoken of in the Bible thus becomes, not the origi'114ti716 of things that did not previous]y exist, but the mere organization, or 4"angement of matter already existing. And as attraction-the supposed agency in this arrange. ment-is still in operation, the creation of all things i. resolved into an ordinary, we might almost say, an every. day occurrence. 2. The supposed c,onsolidation of the nebulous mass, in obedience to the general law of attraction, does Dot itself account for the -rotary motion which is an essential part of the. theory • Under the influence of mere attrae. tion, the particles must tend directly towards the centre of the mass, and consequeI\lly could have no tendency to produce a rotary motion during the process of condensation. S. The variation of the planetary orbits from the plane of the 8un's equator, contradicts the Nebulat theory. If the several primary. planets were successively. thrown off from the general mass, of which the sun is a part, they could not have been separated from the pa.rent body, till they were near the' plane of its eq nator . Now, as the Bun is assumed to l)6 a part or the same mass, revolving still, the theory would require that the portions now separated from him and called or , , 152 LAwa OP PLANBTAllY KOTIOK. planets, should still revolve in the plane of his equator. But instead of this being a (act, it is found that some of them vary from this plane to the amount or near 420. See Lessons 32 and 105, and the maps. 4. Ffhis theory assu mes not only that the primary planets were thrown off from the parent mass by its rapid revolution, but that the primaries in tum threw off their secondary plane\S or satellites. These of course, then, should all revolve in the plane of the planetary equators respectively, and in the direction in which th~ir primaries revolve. But their orbits not only depart from the plane of the eqllators of their primaries, Jupiter's sateUites excepted, (Lessons 70, 81, 82, 83,) but the moons of Herschel actually have a retrograde or back. card revolution. See 83. 5. If the sun and planets are composed what was originally the same mass, it will be necessary to show why they differ so materially in their physical nature-why the sun is self-luminous and the planets opaque, &c. But we have not room to discuss the subject at length in this treatise. It is but justice, however, to say, that men eminent for learning and piety have advocated what is called the Nebular TAeory, in the belief that it was per(ectly consistent with the Mosaic account of the creation or the heavens and the earth. If the opinion or the wri. ter is desired, he is frank to state, that while he acknow. ledges the force of some of th~ considerations urged in its IU pport, he has not yet seen reason for adopting this &hory of the formation of the Solar System. or Lesson III. LAWS O~ PLANBTARY MOTION. (Map 7.) The~e ~re three general principles which govern the lnotlons of all the planets. These were first discov. ~red t,y Kepkr, a German astronomer, from wbom th~y ~- ... -- i LAWI OF PLANETARY aOTION. 15'3 ha ve since been called Kepler' 8 lafIJ8. They are as fol. lows: _1. The orbit. of the Earth, and aU the PiaU", are ELLIPSES, having the Sun in the common IDea •. "The ellipse is a curve, of an oval or elongated form, all the points of which lie in the same plane. The largest diameter of an ellipse is called the major,' or tra1l8Verae tuU. It divides the curve into ,two equal parts. The foci are two points in the transvene ax~ equally distant from the centre. If from any point or \ the curve two lines be drawn to the two foci, their 8um will be equal to the transverse axis. Since ~e sun is in one of the foci of the elliptical orbit of a planet, the latter will, at different times, be at unequal distancel from the sun." At whatever point in its orbit a planet may be, a line drawn from its centre, to the centre or the sun, is called the radiw "ector. 2. The radiua "ector, (or line dra1Dfl from t1&e centre of the Sun to the centre of aftY Planet re'OoZ"iftg around it, l describea equal areaa i~ equal time,. The nearer a planet is to the sun, the more rapid itt motion, (19.) It follows, therefore, that if the orbit at a planet is an ellipse, with the sun in one of the foci, its rate of motion will be unequal in different parts of its orbit,-swiftest at perihelion, and slowest at aphelion. From perihelion to aphelion, the centripet~l more direct. . Iy counteracts the centrifugal force, (20,) and the pla.net is retarded. On the other hand, from the aphelion to the perihelion point, the centripetal and centrifugal forces are united, or act in a. similar direction. They consequently basten the planet onward, and its rate 01 motion is constantly accelerated. Now suppose when the planet is at a certain point near its perihelion, we draw a line from its centre to the centre of the sun. This line is the radi'IU "ector. At the end or one day, for instance, after the planet bas advanced considerably in its orbit, we draw another line' in the same manner to the sun's centre, and estimate the area between tbe two lines. At another time when the planet is near its aphelion, we Dote the space over which -------~ .. 154 LAWS 01' PLAl'fBTAB.Y J[OTION. the radius vector travels in one day, and estimate its area. On comparison it will be found, that notwith. standing the unequal "elocitg of the planet, and con. sequently of the radius vector, at the two ends of the ellipse, the area ove~ which the radius vector has trft velled is the same in both cases. The same principle whatever obtains in every paJ1..of the planetary or may be their elliptioity or the mean oC the planet from the sun; henCe the rule, that tAe JlJa~u ducrilJe. equal area ;11 equal time,. * 8. TM .quare. of the penodic limu are ~ IAe mea1l tlUtatU;u from tAe SUfi. ce Take, Cor example, the earth and periods are 865.2564 and 686.9796 days, distances Crom the sun are in the pPln>.,."."j~. 1.02369; and it will be found that (365.2564)2 : (686.9796)2 : : (1)1 : (1.528~[IJ "The m8.81 of the earth being Car smaller tha the sun, the mOOD de~cribes a proportionally smal round it in a -moment of time. "So, Herschel, Saturn, and Jupiter having greate than the earth, their satellites make greater their primaries, in a moment of time, than our round the earth. Still, this third law of Ke in each secondary system. Among the sate same system, the squares of the periodical ti ways as the cubes of their mean distances mary of the system." According to these laws, which are known to prevail throughout the ~lar System, many of the Cacts of astron. omyare deduced from other facts 'previously ascertained. Th~y are, therefore, of great importance; and should be studied till they are, at least, thoroughly understood, if not committed to memory. The first is illustrated in several or the maps, and, as before said, the ingenious teacher will readily illustrate the second by a simple diagram upon a slate or black.board. It would be a very useful exercise for the pupil to test the table in which the ~---------- IlEPB,£SBN'TA.TION OF THB SOld-a SYSTBM. _ l. 56 dUtIl"ce. and periodic time, are given, by this third law-. See Lessons 8 and lB. Lesson II".· MINIATURE REPRESENTA.TION OF· THE SOLA.R SYSTEM. At the clo~ of his remarks·on the Primary Planets,· Sir John Herschel has a most graphic and interesting d~cription of the Solar System in miniature, which is bere inserted for the perusal of the learner. Choose any' well-levelled field or bowling-green. Oft it place a globe two Ceet in diameter: this will represent the SUD; Mercury will be represented by a grain of mustard-seed, on the circumference of a circle 164 feet in diameter for its orbit; Venus a pea, on a circle 284 f~.t in-diameter; the Earth also a pea, on a circle of 480 feet; Mars a rather large pin's head, on a circle of feet; Vesta, Juno, Ceres., and Pallas, [also Astnea,] -"grains of sand, in orbits of 1000 to 1200 feet; Jupiter a moderate-sized orange, on a circle nearly half a mile acrose; Saturn a small orange, on a circle of fouI-fiftbs of a mile; and Herschel a full-sized cberry, or small plum; upon a circumference of a circle more than a mile and a half in diameter. • • • • • To imitate the mot:ioM of the planets, in the above. mentioned orbits, MercurY must revolve in its orbit in 41 seconds ; Venus in 4 mht. 14 sec.; the Earth in 7 min. ; Mars in 4 min. 48 sec.; Jupiter in 2 h. 56 min.; Saturn in 3 h. 13 min.; and Herschel in 2 h. 16 min. So far as relative magnitude is concerned, it will be easy to discover the general accuracy of Maps 2 and ~, according to the representations of Dr. Herschel, all above quoted. It is proper, however, to remark, that the maps were d rawn by -the author by a regular and exact scale, without any reference to the foregoing, or any recolleoits existence. tion 8:?J. or . \ - • Treame, p. i7L • - 156 ORIGIN OlP THE ASTEROIDS. Lesson 113. WERE THB .lSTEROIDS ORIGINALLY ONE PLANET' I. Some very curious speculations have been enter.. taiDed by astronomers in regard to the origin of the Asteroids. As in the case of the recent! y discovered planet Le Verrier, the existence of a large planet between the orbits of Mars and Jupiter was 8uapected before the Asteroids were known. This suspicion arose mainly from the seeming chasm that the absence of such a body would leave in the otherwise well. balanced Solar System. 2. The prediction that such a body would be disc<wered in the future stimulated the search of astronomers, till at length, instead or one large planet, five amall emu' were one after another discovered. For the time of their dis. covery, see Lesson 67. . 8. From' certain peculiarities of the Asteroids, it haa beeQ considered highly probable that they were originally one large planet, which had been burst asunder by some great convulsion or collision, and of which they are the fragments. The grounds of this opinion are as follows: (1.) The Asteroids are much.maller than any of the other primary planets. · Lesson 14. (2.) They are all at nearly the same tlirituace from the BUn, as will be seen by Lesson 8. (3.) Their periodio revolutions are accomplished in nearly the same time. (Lesson 18.) The difference their periodic times is Dot greater than might result from the supposed disruption, as the parts thro~DforZDard would have their motion accelerated, while the other parts would be thrown back or retardBd;. thus changiog the periodic times of both. ( 4.) The great departure of the orbi18 of the A steroids (rom the plane of the ecliptio is supposed to favor the hypothesis of their having been originally one planet, the assumption being that the explosipD separating the ori. ginal body into fragrnenta would not only accelerate some portions and retard others, but would also throw them out or ---..., 157 OI.IGIK OP THB AS'I'BI.OIDS. of the pI ane of the original orbit, aod in some cases still further from the ecliptic. (5.) Thei}\ orbits are more eccentric than those the other primaries, (46.) Although the table shows the eccentricity of Herschel's orbit as greater in miles than that of even Juno or Pallas, yet when we coDsider- the difference in the magnitude of their orbits, it will easily be seen that his orbit is less elliptical than theirs. (6.) The orbits of Ceres and Pallas, at least, cr08' eacl other, as shown in Map 2. This, if we except perhaps the orbits of the comets, is a perfect anomaly in the Solar or 8ystem~ From all these circumstances, it has been concluded that the Asteroids are only the fragments of an exploded world, which have assumed their present Corms &iDce the disruption, in obedience to the general laws of gravitation. This theory of Dr. Olbers, is favored by Pror~ Nichol, Dr. Brewster, Dr. Dick, and others; while Sir John Herschel observes tha-t it may serve as a 8pecimea of the dream, in which astronomers, like other speculators, occasionally and harmlessly indulge.· Dr. Dick remarks, that the breaking up of the exterior orust of the earth, at the time the gelleral deluge, was a catastrophe as tremendous and astonishing as the burstin, asunder of a large planet. _ The late General Root, of Delhi, was of opinion that the Asteroids were primarily,atellite, c!f Mar, j which, as if dissatisfied with their low oondition as mere attend. ants upon anotber, and one, too, not lQuch larger than themsel ves, ha va wandered from their original spheres, and assumed the character of primaries. The rea.01I8 for this opinion, 8S stated to the author by Gen. Root, in the fall of 1846, are quite as satisfactory 88 the evidences by which the theory of Dr. Olbers is supported. But this is Dot endorsing either the one or the other. Indeed, in view the karrrumyand order that everywhere reign throughout t he planetary regions, directing the pathway and CODtrolling the destiny of every world, it is hard to believe or t - or • Treati_, p. Ita t Ce1_ial SceneryJ p. 140 14 - 158 AIlB TBB PLANBTS lNBABITBD' tbat any planet has either been broken to pieoes by SOlll8 mighty explosion or concussion, or wandered from its presoribed path into a Dew and esaeotially different orbiL Lesson I ItI. I ..lRB THB PLANBTS INHABITED BY RA. TIONAL BEINGS 1 U poD this intereating question, it must be admitted, that we have no positive testimony. The argument in tbe affirmative is baaed wholly upon analogies, and the 'conclusion is to be regarded ooly in the light of a legitimate inCerence. Still, it is remarkable tba.t those who are best acquainted with the facts .astronomy are most confident that other worlds, as well as ours, are the abodes of intelleotual life. Indeed, as Dr. Diok well remarks, it requires a minute knowledge of the whole aceoery and circumstances connected with the planetary system, before this truth comes home to the understand. ing with tull conviotion. It is ·Dot proposed, in this lesson, to discuss at lengtltbe question of a plurality of worlds, but merely to give the beads of tbe arguments by which this doctrine is 8Upported, leaving the reader to amplify them by reflection, or to pursue the inquiry, at his leisure, in more elaborate works. Perbaps no ~riter hu done better justioe to this subject than Dr. Dick,· to whom we are in. debted Cor many of the arguments with which this lesson is enriched. . 1. The planets are all ,olid bodie, resembling the eartb, and Dot mere clouds or vapors. . 2. They all ha va a aplierical or .,1&,roidal figure, like our own planet. 3. The laws of gravitation, by which we are kept upon the surface of the earth, prevail upon all the other planets, as if to bind races ot material beings to their surfaces, and provide tor the ereotion of habitations and other conveniences of life. or • Celedial Scenery, pp. 331-363 159 ARE THB PLANBTS INlU.BITB'D 1 4. The magnitude, of the ,lanets are such as to aWord ample sQOpe {or the abodes 0 myriads of inhabitan,ts. It is estimated that the solar bodies, exclusive of the comets, contain an area of 78,000,000,000 of square miles; or 397 times the surface. of our globe. According to the population of England, this vast area would afford a resi. dence to 21,875,000,000,000 of inhabitants; or 27,000 times the population of our globe. 5. The planets have a diurnal re"olution around their axes, thus affording· the agreeable vicissitudes of day and night. Not only are they opaque bodies like our globe; receiving their light and heat from the 8UD, but they also . reTolve. 80 as to distribute the light and shade alternately over each hemisphere. There, too, the glorious SUD arises, to enlighten, warm, and oheer; and there "the sun.strown firmament" of the more distant heavens i. rendered visible by the no less important blessing of a periodic night. It is very remarkable, also, that those planets whose bulks are such as to indicate an insupportable attractive force, are· not only less dense than our globe, but they have the most rapid daily revolution; as if by diminished density, and a strong centrifugal force combined, to re. duce the attractive force, and render locomotion possible upon thei r surfaces. 6. All the planets have an annual re"olution round the sun; which, in connection with the inclination of their axes to their respective orbits, necessarily results in the production of seasons. 7 . The planets, in all probability, are enveloped in atmosphereB. That this is the cale with many of them is certain; and the fact that a fixed star or any other orb is nbt rendered dim or distorted when it approaches their margin, is no evidence that the planets have no atmosphere.. This appendage to the planets is known to vary . in density; and in those cases where it is not detected by its intercepting or refracting the light, it may be of a nature too clear and rare to produce such phenomena. 8. The principal primary planets are provided with moons or 8atellite8, to afford them light in the absence of • 160 .AU 'fBB PLANBTS INBA.BITBD' the 8un. It is Dot improbable that both Mars and Venul bave each, at least, one mooD. The earth has ooe, and as the distances of the planets are increased, the Dumber of mOODS seems to increase. The discovery of only six around Herschel is no evidence that others do not exist which have Dot yet been discovered. 9. The surfaces all the planets, primaries as well u secondaries, seem to be variegated with Aill dt&le, With mDrInUJira and plain. Every Fart of the globe we inhabit is destined to the IUpport 0 animal life. It would, therefore, be contrary to the analogy nature, as displayed to us, to sup~ that the other planets are empty and barren wastes, utterly devoid of animated being. The inquiry pre_es itael f upon the mind with irresistible force, Why should this one small world be inhabited, and all the reBt unoc. oupied 7 For what purpose were all these splendid rmd magnificent worlds fitted up, if not to be inhabited 1 Why these days and years-this light and shade-these atmo.pheres, and seasons, and satellites, and hill and dale 'I The legitimate, and almost inevitable conclusion is, that our globe is only one of the many world. which God haa oreated to be iohabited, and which are now the abodes bis intelligent oftSpring. It is revolting to suppose that we of earth are the only intelligent subjects of the " GRBAT KING," whose dominioDs border upon infinity. or au or or i I • I i I PART II. THE SIDEREAL ·HE! VENS. , CHAPTER I. ' OP CONSTELLATIONS OF STAKS. Lesson 113. DISTINGUISHING CHA.RACTERISTICS OP THB PIXBD STAllS. Sidereal Heavens embrace all those celestial bod. i"a. that 'lie around and beyond the Solar System, in the region of the Fixed Stars. ' The l?ixed Stars are distinguished from the Solar Bodies by the following characteristics : 1. They shine by their DUm light, like the SUD, and not by reflection. 2'. To the naked eye they seem to' t7Dinkle or scintil. late; while the planets appear tranquil and serene. 3. They maintain the same general positiDn8 with re. .pect to each other, from age to age. ' " ,. They are inconceivably diatant, 80 that 'When view.. ed through a telescope they present DO sensible disc, but appear only as shining points on the dark concave of the THE • , . t sky. . . To these might be added several other peculiarities which will be noticed in the seq uel, but they are not no- "oessary to our present purpose. Lesson 116. or. THE ,,(Map 16.) CLASSIFICATION STAllS. For purposes or convenip,nce in finding or rererring to particular stars, recourse is had to a variety artificial 14'" or 162 CLASSIFICA.TION OF THE STA.IlS. Dlethods of claasification, with which the pupilsbould here become acquainted. . 1. The whole concave of th~ heavens is divided into IeCtions of greater or less ext~nt, called C0f&8tellat:ioru. ~'or the origin of these most uDnatural and arbitrary divisioDs, consult Lesaon 36. A list of the constellations will be fouod in a subsequent chapter. 2. The stars are all classed according to their magaitude.. There are usually reckoned twelve different magnitudes, of which the first six only are visible to the naked eye, the rest being telucopic This magnitude, of course, relates only to their apparent brightness, 88 the faintest star may appear dim solely on account of ita immeasurable distance. Fig. A on the map is a representation of the first eight lDagnitudes, the two smallest of which will be invisible to the pupil at a distance. " It must be observed," says Dr. Herschel, "that tbis classification into magnitudes is entirely arbitrary. Of a multitude of bright objects, difrering, probably, intrinsically both in size and in splendor, and arranged at unequal distances from us, one must of necessity appear the brigbtest; the one next below it brighter still, and 80 on." 8. The next step is to classify the stars of eack COMtel laticm according to their magnitude in relation to eacA other, and without reference to other constellations. In this classification the Greek alphabet is first used. For instance, the largest star in Taurus would be marked (a.) Alpha; the next largest (~) Beta; the next (r) Gamma, &c. When the Greek alphabet is exhausted, the Roman or English is taken up; and when these are all absorbed, recourse is finally had to figures. 4. To aid still further in finding particular stars, and especially in determining their numbers, arid detecting "hanges, should any occur, astronomers have constructed Cata/.ogtJU of the stars, one of which is near 2,000 yean old. 5. Several of the principal stars have a specifio name like the planets; as Siriua, Aldebaran, Regula, &c. 6. Clusters of stars in a constellation sometimes . re- .tar.. I 163 KVIIBBa OP TBB paEl) &TAIlI. ceive a specifio name, as the PleiGdu and H,atlu iD Taurus. 7. The stars are still Curther distinguished into Dou ble, Triple, and Quadruple stars; Binary System; Vatiable Stars; Periodic Stars; Nebulou8 Stan, &c.; all or which will be duly Doticed as we proceed. But we must the 8tarry first consider the more general divisioDs heavens. or Lesson 117. 5VMBBB. OF THB PIXBD STABS. The actual number of the stars is known only to Hi.. who" telleth the number of the stars," and " calleth them all by their names. JJ The powers of the human mind are barely sufficient to form a vague estimate of the number Dea~ enough to be aeen by our best telescopes, and here our inquiries must And. The number of stars down to the twelfth magnitude, has been estimated as follo\vs : 18 1st magnitude, Visible to 2d" 02 3 d " 177 the naked 4th" 376 eye, 5th" 1,000 6th" 4,000 5,628 7th 26,000 " u 8th 170,000 Visible 9th 1,100,000 " only thro' 7,000,000 " tel 'scopes, 10th 11th 46,000,000 " 12th 300,000,000 " 354,296,000 Total number, 854,301,628 Orthese stars, Dr. Herschel remarks that from 15,00(1 to 10,000 or the firAt seven magnitt:des are already, regu• • red, or DOted down in catalogues; and ProC. Olmated 164 DIITANC.B8 OP TUB STABI. observes that Lalande haa registered the positions or no less than 50,000. " If we suppose," says an eloquent writer, "that each or these SUDS is accompanied ooly by as many planets as are embraced in our Solar System, we have _fifJ6 t/unu"nd, ",illio'M of tDOrlU in our firmament. No human mind can form a conoeption or this number; but even these, as will hereafter be shown, form but a minute and comparatively insignificant portion of the boundless empire which the Creator has reared, and over which he reigns. EterDal ages may glide joyfully along, as the Christian explores these wonderful worlds; of every variety of form and character, and partakes of the hospitalities of their blissful inhabitants. I t is pleasant to tread the pavements of a foreign citY-1n traverse the glaciers of the Alps-to glide over the surface of the Nile in the midst of the mouldering remains of its past grandeur; but what are all these, compared to the journey of a rejoicing spirit to these sublime mansions of the Deity 1" Lesson lIS. DISTA.NCES OF THE STA.RS. It has been demonstrated that the nearut of the ~ stars cannot be less than 20,OOO,OOO,OOO,OOO-ttDtnty billi0f&8 of miles distant! For light to travel over this space at the rate or 200,000 miles per second, would require 100,000,000 seconds, or upwards of three years. What then must be the distances of the telescop~o stars, of the 10th and 12th magnitudes! "If we admit," says' Dr. Herschel, "that the light of a star of each magnitude is half that of the magnitude next. above it, it will follow that a star of the first magnitude will require to be removed to 862 times its distance, to appear no largeJ than Olle of the twelfth magnitude. It follows, therefore, that among the countless multitude of such stars, visible in telescopes, there must be many whose light has taken at least a thousand years to reaclI U8; and that when we observe their places, and note their chan2es, we are, ill KJ.GNITUDB OP TBB STAB•• 165 ract, reading only their history oC a thousand years' date, thus wonderfully recorded.'~ Should such a star be struck out oC existence now, its light would continue to stream upon us Cor a thousand years to come; and should a new star be created in those distant regions, a thousand years must pass away before its light could reaoh the Solar System, to apprize us of its existence. Lesson 119. • MAGNITUDE OP THE STABS • .,. From what we have already said respecting the almost Inconceivable distances of the fixed stars, it will readily be inferred that they must be bodies of great magnitude, in order to be visible to us upon the earth. It is probable, however,' that "one .star ditTereth from another" in its in• . . trinsic s'pleDdo~ or "glory," although we are not to infer that a litar is comparatively small, because it appears small to us. The prevailing opfnion among astronomers' is, that wha.t we call the fixed stars are so many BUU, and oentres of otber systems. By a aeries of experimeots upon the light rece~ved by us Crom Sirius, the nearest of the fixed stars, it is ascertained that if the IUD were removed 141,400 times his present distance from us, or thirteen billions of miles, his light would be no stronger than that of Sirius; and as Sirius is more than twenty billions of miles distant, he must, in intrinsic magnitude and· splendor, be eqUfll to two S\1D8 like ours. Dr. Wollaston, as cited by Dr. Herschel, concludes tbat this star must be equal in intrinsic light to nearly fourteen 8UD8 f According to the measurements Sir Wm. Herschel, tbe ·d~ameter tbe star Vega in the Lyre, is 38 times that the sun, and its solid contents· 54,872 times greater! The star numbered 61 in the Swan, is estimated to be 200,000,000 miles in diameter. Sir John Herschel states that while making observa. or or or 166 LIST OF TO CONSTB.LU.TIONS. .y. tions with his forty.feet reflector, a star of the first magnitude was uninteotionally brought into the field of view. " Sirius," he, "announced his approach like the dawo of day j" and 10 great was his splendor when ~U8 viewed, .and 10 atrong W88 his light, that the great astrooomer wu actually driven from the eye-piece of his teleecope by it, 88 if the SUD himself had suddenly burst upon his view. He was obliged to employ a coloted screen, as in the case ot solar observatioDs, to protect bis eye from the strong and glowing radiance. According to Sir W m. Herschel, the relative light of the stars of the first six magnitudes is as follows: Light of a star of the a verage 1st magnitude 100 " " "2d" 2.'i " " " " " " "3d" "4th" "5th" " " "6th" 1~ 6 2 1 Lesson 1 "0. LIST OF THE CONSTELLA.TIONS. Of the natUN and orWi" of the constellatioDs we have already spoken in LessoD 36. Their Cormation has beeD the work of ages. Some of tbem were known at least 8 t OOO years ago, and bore the very names by which they are known to this day. In the 9th chapter of Job we 'read of " Aroturus, Orioo, and Pleiades, aDd the chambers of the BOuth ;" and in the 38th chapter of the same book, it is asked, "Canst thou bind the sweet influence8 of Pleiades, or loose the bands of Orion 1 Canst thou bring forth Mazzaroth in hi, _&sOn 1 or caoat thou guide A rcturu8 with his sons '" : At first tb•. number of constellations was few. Being found convenient in the study of the heavens, new; ODes were added to the list, composed of stars not yet made up .1oto hydras and dragons, ~ill there is now scarcely stars or room enough left to coDstruct the smallest ne" constellation, in all the spacious heavens. 167 CONSTBLLATIONS. The constellations are divided into the Zodiacal, the NlWtAern, and the Southern. The Zodiacal C0f&8teilatiou are those which lie in the Bun'S apparent path, or along the line of the Zodiac. See Leason 86, and the map. The Northern COMtellatiou are those which lie be. tween the Zodiacal and the North Pole of the heavens. The Southern Constellati01I.8 lie between the Zodiacal . and the South Pole of t.he heavens. The oonstellations are also distinguished into ancienl and modem. The following is a list of all the constelJations, both anoient and modern, with the number of principal sl.ars in each, according to Ptolemy's Catalogue, and al_\1 that of the Observatory Royal of Paris. I. ZODIACAL CONSTELLA'l'IONS. Latin Dam•• 1 'f AR.I ... JJ ~ rAuaua. 3 .0 GBM1NI. En,lilh nam.. Th.e Ram. The Bull. Tltt~ T1Din... .. ~ CANCBL T}It~ 5 £'\. Lao. ft rfJl V111.00. The Tht! "I 6 8 f11. L,BRA. T"~ SCOR.PIO. Th« Tht Th« Tht Th« Ful&tl,. 9 10 11 11 I SAOI'M'Akb'" ~ CAPlUOOKI'!.UIL = * AQl1AR.lbli. fJM:l: .. Crab• Lion. l"irgin. Sr.al«. Scorpion. Archer. Goat. Water-Ntlrer. Ptol',. Ob. L 18 ~ 44 t07 25 33 &4 85 3~ 93' 117 67 60 94 64 117 118 32 07 27 31 fI8 45 38 II. NORTIIERN PONSTELLATloNS. · ANCIENT • 13 U..A MIKOL 14 UIlM MAJOR. 15 Duoo. 16 CI:PUI:w. 1'1 BooT... . 'I'M Little B«ar 08 II T 1&« Gr,at BtGr. Th, Dr• •,,- 34 87 81 13 23 86 58 C«pJuu. Boot,.. 70 /'68 CONSTBLLA.TION5. LaUta ........ 18 19 20 En,liah a&lD8I. TUAIIG. BollaAI••8. Th, N(Jrth~rn Crown. Hwcvl,•• Tl, Harp. T'" SVJtJ1f,. CfI,nop'",. Pn-.,u. Tl, ChtJriotter. TM S,rpent-b,ar,r. Tk, Arrow. The Eaglt. Tht Dolphift. TA, Littl, Hortle. PtgaftJ'. Antineru. Andromeda. TAe NortA. TNn,. COilA B.alllno_ . B..,·,,"c,'. HtJIf'. CoRONA 80aBLIIL H.acuLa.. LYRA. ~l CYGNUII. 22 CAMior.IA. ~ PBUBU8. 24 AURIGA. 25 26 27 O'HIUCBt1L 18 DELPHINUe. 29 30 EQUULRUB. 31 ANTINOU& 32 33 34 ANDROIIBDA SAGITTA. AQUIlA. • P.OA_va. Plol'l. 08 29 Ob." 33 128 21 10 85 10 13 29 14 29 05 15 10 04 20 15 23 04 35 60 65 69 61 18 26 19 10 91 28 71 15 43 .00 II 8.N. ~ CUI'f08 M_luII. TI&e Liul, Lioft Tie Grey!&QURtU TI&e Sezttl1lt Cer6eru... PonitJt01lJ,lci, Bull. TAe Foz lind 000• . TA-e Lisard. Th, Littl, TrilJngk. Ti, Northern Fl,. Tie Reindeer. The Ha.rve.tn-. 46 CAIiBLOPAaDALU" T~ " LIla. 35 Lao MINOL 36 CAN.8 37 SRITAIf.. 38 39 CBRB.aUB. V BNA'I'IOI. TAUILU8 PONIATOW8U 40 VBLPRaULA 41 a,. An. LAoaaTA. ~ TalA.NGULA MDfOU. 43 MUIIOA Do.SALIIL " TAaANDU& 56 38 54 13 18 35 12 04 05 Ii 07 69 CtJmelopartJ TIN Lynz. 45 III. S(lUTBERN ~()NSTELLA TIONS. ABel.lIfT. 48 e C.,.t1L EaIDA.1'W& TIN WAllie. TIN RiDer Pe. " 19 34 1. 81 ;' 169 aoKft&LL.A.'lJOXI. La....__ !O Ouo•• . 61 Law. 61 C. . . MmoL 13 C.... Muoa. "Auo 65 N~... BYD. . . 16 CUT... 57 Coan.. 58 C&Jft'Auaa 59·LuJw. &0 Aa~ 61 CoaoRA Au.raALI& • ~PuIola AU8ftALIJL ,,1iI1a ..... PloI ... ab." Orion. TA. Har•• 3e Ii SO Tie Little Dog. og 17 TA. (hea' Dog. TAe 81i, Argo. Tie Water S.,.,..t. I'll C.,. Tie Oro",. Tie e••tGw. TAe Wolf. 7'1. Alt"r. Tie 80utlena Cro.,.. TJu 80utlunt F'-l. 19 45 54 07 10 48 90 117 WI 5i 07 13 37 19 07 34 08 13 Ii 18 24 The CA..it:. Pu,.,.. TIe RAMI,bed N.t. Tie B"f'rfJ"'!'"'- TooL TM ~u"".tl-.fi.A. TAe DOfJe. TIe Painter', Ba,L TAe Unicom.. Th, Mariner'. COfIIptI& Tile Air-pump. Th, SolittJry Bird. The Southern Cro". 'l'Ae SoutAn-n Fly. Tie CIuJ""leora. TM Flying-ful. Tlu Te~e.co~. TIe Pe"dlJ,~IJ"', fc:. Euclid', Square. TM Compa"e,. Th, SoutAI'm TriGftgle.Tie Bird of ParGdUe. .nnt of Table Ba,. 8olM.k,'. BIa.tIe 39 MODERB. G Fouru CmmoA. " 15 I . Rft'lOVLI8 Ruo. . . C.L& SOULrrOU.. XrPIL 66 67 68 EQVUL&U8 PlOT. 69 MONOCB&08. 70 11 71 13 14 15 76 77 18 19 80 81 82 83 84 PYx.. NAU'I'IOA. AUTLIA PN&VJlAT. Ana SOLl'l'. Cavx AU8TL\LI& MWCA AU8TULItI Do...DO VaL COLOIOA NOACBI. CB~ •• L.ONI& Pilei. VOLUl.. T&LUOOPIUK. I HOROLOGIUII. NORllA EuOLID. . Claollwa. TaJAlfa. Au.,.."'. Ap. ftL Ay.I.DICA. Mo. MaM8ouft. a....... 85UD1J8 86 PAYO. - TAl 1""__ Tie P4tMJOCi. 15 -- 07 15 08 Oi 04 31 14 ~ •oa 04 07 06 08 23 15 Oi 05 CM oa 18 04 11 170 ... OP TUB P.1lI01P.A.L OOlISDLLATIOlfS. n. ftoFL Ob. a. -~ OettIrtL - 07 08 12 11 88 Mroll.OllOOftUJL BIG... TIe.~. 90 TovoJWlf~ TA. A.er. Goo... TIe W.",......k.. - . 08 Tie ScalptGr'. SttuJio.. 18 11 Tie PJuaJlis. TIe Cr. . . 91 BuaUII. n APP~&A'l'U8 Souu. 91 PaabtJL - RECAPITULATION. Zodiacal eon.tenaticms, 12 Northem" 35 Southern" 46 Principal stars, " " " Total, 3706 Total, 93 Lesson c, 1125 1531 1050 1~1. DBSCJUPTION OF SOU OF TBJ: PRINCIP....L CONSTBu..TIOllS. Although this work is designed particularly to Ulo8trate the Mechanism of the Heavens, as displayed ill the Solar System, we are desirous of furnishing the learneJ with a sufficient guide to enable him to extend his inq oi. ries and investigations, not ooly to the different cltU8U of bodies lying beyond the limits of the Sola"r System, in the far-off' heavens, but also to the Con8tellations as such. For this purpose we shall here furnish a brief description of the principal constellations visible in the United States, or in north latitude, by the aid of which the student will be a.ble to trace them, with very little di~cu1ty, upon "that glorious celestial atlas· which the Almi~,hty bas apreari ,out before us. These des9riptiool are partly original, and partly from the writings of Olmsted and Burritt. . ZODIA.CAL CONSTBLLA.TIONS. The Constellations or the Zodiao, succeeding each other in "regular order ea8tward, and being more eMily found OD that account than others, should first be studied_ .171 ABIB' is a email constellation known by two bright about 40 ..part. which form the head. The brightest is the moSt northeasterly of the two. . . ·rAt1R17S will' be readily found by the seven stars or Pleiades, which lie in' his' n·eck .. The largest star in Taurus is Aldebaran; in tfle Bult's eye, a "tar of the first magnitudet of a' reddj.ah .color, somewhat resembling the planet Mars. AldebaraD, an4 four other stars in the face of Taurus,. oo~pose the HJad,u. They are 80 ,placed lUI to form the. lelter V. GBMINI is known by two very bright stars, CtuIDr a~d Poll~, about five degtees apart. CA.NeB. is lees remarkable 'than any other oonstellation of the Zodiac. It has DO stars larger than the third mag. nitude, and is ~istinguished (or a group or small stora called the Nebula of Cancer, which is often mistaken for a comet. A common telescope resolves this nebula into, a beautiful 8ssembl,age of bright stars~ LEO is a large and interesting constellation, contain. ing an unusual Dumber: C?f'. very brigbt stars. Of these, RegulU8 i~ of the first magnitude, and .lies directly in the ecliotio. North of Regulus are several',bright stars in the form of a siclde, of whioh Regulus is the handle. Denebola is a bright star of the second magnitude, in the Lion's tail. It is about 250 Dorthe~8t of Regulus, and 350 west of Arctur.us. . V I1I.ao extends for I01Jle .distance {rom west to east, but contains only a few bright atars. ' Of these, SpiOll. in the ear or corn which the Virgin holds in her. left hand, ill a brilliant star of the first magn~tude. The rest 01 Iler principa.l stars ~~ of 'the third and fourth magllitudes. , IItars, may be known by its four principal stars, form. ing a quadrilateral figure. The two brightest ~f these constitute the beam of the balanoe, and the slnaU(;st is in the top or handle. . ScoaPIo is one of the moat interelting and splendid of LIBRA J72. BOaTB&mf COlfITBLUftOX•• tbe conltellatioDs. His bead coll8ists of five bright stan, forming the arc of a oirole, and is croSled by the ecliptio near the brightest of the five. Nine degrees lOutheaat is the star AftltJru, or a reddish color, and oC the first magnitude. A number of small &tara that curve around towards the east constitute the tail oC Scorpio. 8AGITT.A.B.1118 lie. next to Scorpio, and may be known by three stan arranged in a curve, to repreeeDt the 60111 of the Archer, the central star being the brightest, and baving a bright Itar directly west of it, fOrming the head the GrTOIfJ. or "- lies northeast of Sagittarius, and may be IE nown by two bright stara c10a.e togetlaer, which 00DSti. CAPJUCOJlNUS I tute the bead. AQU'AJlros is represented by the figure of a man pour. ing water out of a vessel. Its Cour largest stars are tbe third magnitude. Two of these, which lie in a liDe with the brightest stars in Capricomus, constitute the head of the figure. or the last of the Zodiacal constellations, lies be. tweeD Aquarius and Aries. Tbe Southern Fish coosists of 24 visible stars, of which one is the first magnitude, two of the third, and five of the fourth. The remaining 16 ale smaller. The. largest star is situated in the mouth of the Fish, and is called POfIUJ,lAaut. The Northern Fish coosists. wholly of small stars, and is coo. neeted with the Southern by a aeries stan CormiDa a . PISCBS, or CI'OOkeclline betweeD them. or Lessen 1 ••• . IfOKTDJUf CONSTBLllTIOX•• bei, The Constellations or the Zodiac first well learned, 80 as to be readily recognised, will aeUitate the leaming of others that lie north and loutA or them. Let us, therefore, review the principal Nordae,.,. Cou6Jlla. • l IfOJrDlJ&B.R C8JfITBLllTJ01f8. tiou, beginning north of ·Aries and proceeding {rom west to east. or ANDROMEDA. . may be known by three stars the second magnitude, situated in a straight line, and extend. ing from· east to west. ;The figurp is that of a "Woman, with her ar. . est8nded; aad chaiaed by. her wrists to a rook. The middle Itar, of the three just Darned, is . situated in her ginlle,. and is called Mirach. The one west of Miraoh i. in Ute 1IelJIl, of Andromedat aD4 . the eastern one, called Almaak, is in her left fooi. The star in her hea4 Is in the Eq uinocthil Col ure. The three largest stars in this constellation are" of the secondm\agnitude. Near Mirach are two stars of the third and fourth magnitudes, and the three in a. row cons~itute the girdle. . The loose assemblage of ~man stars directly souih of Mirach, are the Northern Fish, alraady describ~d . . lies directly north of the Pleiades; and east of Andromeda. The ~ure is that of a man with a sword in his right hand, and the he'ad of Medul& in hi. left. A bout 180 from the Pleiades is Algol. a star of the second magnitude, in the head of Medusa; and 90 . north. east of Algol' is .A~ef&i1J, of the same magnitude, in the back of Perseua. It bas, also, {our stars of the third magnitude. . Algol will be mentioned again, under the head· Variable Stars. PBXSB11S or A lJRIGA. ( The Wagoner) is the figure of a man in a declining posture, resting one foot upon the hot-n of Taurus. It is nQrth of Taurus and Orion, and directly east of Perseus. Capella, the principal star in this constella. tion, is one of the most brilliant in the heavens. It is in the west shoulder of Auriga, and may be known' by a · small triangle near it, formed by three small 8t~rs. The LYNX comes next in order, but presentp bothing particularly interesting, as it contains no stars abt>ve the fourth magnitude, and even" theie are scattered over a • 15* ----- -- --1 174 KOaTIIBJUf COJISTBLLA.T10lfl. or large apace north Gemini, and between Auriga and Ursa Major. LBO MINOR is oomposed of a fe~ small stars lying between the sickle in Leo, and the Great Bear. COMA.. BBllBNICBS i. a beautiful cluster of small stars, Dorth of Denebolis; in the tail of the Lion, aDd north 01 the head of Virge. It has but ooe star as large 88 the fourth magnitude. Cor Caroli, or Charles's Heart, is a bright . r about IjO direotly north of Coma Berenice•• or is the figure i. man ~ith a olub in his right hand, with" which he seems to be driving the Great Bear round the pole of the heavens. He is thence called the Bear Driver. -ARCTURUS, situated near the left knee, is a star of the 'first magnitude, and of a reddish color. He is accompaDied by three small stars, (his" sons, "*) which (arm a triangle a littl-e to the southwest. A star of the 'second magnitude is in the head of the figure, and two bright stars of the third magnitude form the shouldel"8. CORONA. BOB.BA.LIS (The CrOfDft) is situated betWe8D Bootes on the west,' and Heroules on the east. It CODlists of six prinoipal stars, in the form of a wreath 0) BOOTBS j I OroWD • .Alpk4t;ca, the largest star or the group, is of the third magnitude, and may be known by its position in the cen. tre of the crown, as well as by its superior brightness. HERCULBS lies immediately east of the crown, and occnpies a large space in the Northern hemisphere. The .figure is that of a giant, with ,a large olub in his right hand. The head is towards the south. This constellation is thickly set with stars, the largest which is called Raaa/gethi, in the head of the figure, and is or the second magnitude. It has nine stars of the third magnitude, and nineteen or the (ourth. or OPBIUcltuS ( TM Serpene.1HJtlrtr) is situated direcdy lOuth of Hercules, with its centre nearly over the equ~ tor, and nearly opposite to Orion. The figure i. that , . or. • Job uniiL 31. NOB.TBBJU'f CONSTBLL.l.TIONS. 1 7fJ yeuerable-looking mao, grasping a serpent in hi' hand., the lead of which consists of three bright stars, situated • little south of the crown. The fouu of the serpent may be traoed by a succession of bright stars extending for aome distance to the east. The principal star in Ophiuchul is of the second magDitude~ and is called ~ Al1aague. It is situated in the Aea.tl of the figure, and within 6 0 of Rasalgethi, in the head of Hercules. (The Eagle) is conspicuous for three' bright stars in its neck, of which the central one, Altair, is a brilliant white star or the fiNt magnitude. Antinoa lies AQUILA directly south of the Eagle~ and nonh of the head of Caprioomus. DELPBINU~' (The Dolphin) is a beautiful little cluster of stars, a little to the ·east of the Eagle. It may be known by rour principal stats in the head, of the thi~d magnitude, arranged in the figure of a diamond, and pointing northeast and south west. A star of the same magnitude, about 50 south, makes the tail~. is a large constellation situated between the Dolphin and Eagle, on the west, and Andromeda aD~ the Northern Fish, on the northeast. The figure is that of a winged hqrae, in an inverted posture. It may be known by four stars about 160 apart, forming a 8quare called the square of Pegasus. They are of the second and third magnitudes, and one .of them, viz. .A~enib, bears the same name as a star in Perseus: PBGASl1S or The HORSE'S HEAD is a small cluster ot stars, w~si the head of Pegasus, and about half way to the Dolphin. It contains ten stars, of which the rour principal are only of the fourth magnitude. They form a long irregular sq uare, the two in the DORf? being 10 apart, and those in the ey~s 2lo. These four stars are about 10 southeast of the diamond in the bead of the Dolphin., , We DOW come to notice the constellations around the 176 lf01lTJlBJlK CO~LLATIONS. North Pole, and which are always above the horizon in llorthem latitudes. (TM LiIJk B84r) is Dear tb. north pole of the heavens. It cODsiRts of the Po~ &ar, 88 it is oall. ed, which CorlD8 the extremity of the tail, aDd six other principal &tan, three of the'third, and four of the fourth magnitudes. The se.en together are arranged in the Corm of a dipper, with the Pole Star in the end of the Uau MINOR handle. URSA M.vOB (7'118 Great Bear) may be known by the figure of a larger dipper, which constitutes "tbe hinder part ot the animal. This dipper, also, is composed seven stars. The first, in the end of the handle, is called BenetfuJ8A, and is of the second magnitude. The ne:Kt is Mizar, known by a minute star almost touching it, called . Alcor. Mi~aT is a double star. The third in the haudle is Aliot". The first star in the bowl of the dipper, at the j unction the handle, is Megrez. Passing to the bottom of the dipper" we find Phad and ¥erak, while Dubhe forms the rim' opposite the handle~' Mer~ and Dubhe are called the Pointer.;, because they always point towards the Pole Star. . The head of the Great Bear lies far to the west of the Pointers, and is ~poeed of numerous amall stare; while the fB~t are severally composed of two 8Dlall stars, very near to each other. or or Duco (T1te Dragon) f'compasses a large circuit iD the polar region.. He winds round between the Great and Little Bear, and commencing with the tail, between the Pointers and Pole Star, it is easily traced by a succession of bright stars extending from west to east; passing under Ursa Minor, it retutns westward, and terminates in tour stars which torm the head, Dear the foot of Hercules. These four stars are 3°, 4°,~nd 50 apart, 80 situated as to form an irregular square; the two upper ones being the brightest, and bdth" the second mag"nitude. or or 'ies east of th~ b~east Draco, but has n ' Itare above the seco)Jd magnitude. "The figure is" that ~ CEPHEUS IOUTD. . OOKSTBLUTlOK8. 177 a iing, crowned, and with a sceptre in his left hand, which is extended towards Cassiopeia. is a queen on a throne or ohair, with ber head and body in the Milky Way. The chair is composed of four stars, whioh form the legs, and two consti. tuting the back. Five of these are of the third magnitude. CASSIOPBIA. LYIL& ('lle Lyre) is distinguished by one of the bright- est stars in the northern hemisphere. It is situated eut of Hercules, and between' him and the Swan. Its largest star is Vega, or Alpha Lyra, and is of the first magnitude.. It has two others of the second magnitude, and several of the fourth. (The StDafl) is situated direotly east of Lyra. Three bright stars, which lie along the Milky Way, form the body and 'leek of the Swan; and two oth~rs, in a line with the middle one of the three, constitute the tDifl81. 1 t bese five stars form a latge cr088. . Arided, in the body 'Of theS'wan, is a star of the first magnitude~ and the .remaining o!les of the constellatioD. are of the third and fJurth magnitudes. CYGNUS CA14ELOPARDALUS (The Camelopa'lJd) is alar ge and UD- interesting field of small stars, scattered between Perseu.. Auriga, the head of Ursa Major, and the Pole Star. Ita five largest stars are only of the fourth magnitude, the principal of which is in the thigh. The head of the ani. mal is near the pole. The LYNX also is composed' of small 8tars; scattered over a large extent. It lies north of Gemini, and between A.uriga and Ursa Major. Its three largest stara are ot the third magnitude. MIiSOD 1~3. SOUTHERN CONSTELLATIONS. The Southern Constellations art' comparatively few,. Dumber, though lOme of them are very beautiful. 1~8 MOT_aN COftSDLLA'ftON8,. (7Ie Whale) i. tbe largest constellation in the heavens. It is situated below or 80Uth of .Aries. It is represented with its bead to the east, and extends 500 east and west, with an average breadth of 20°. The head of Cetus may be known by five remarkable stars, 40 and 50 .apart, and 80 situa.ted as to form a regul~r pentagon, or five-sided figure. Menkar, of the second magnitude, in the nose of' the )fhaJa, is the largest star in the group, or in the cooatellation. ,4' ORION lies south oC Taurus, and is one of the most conspicuous and beautiful of the constellations. The 'gure is that of a man in the act of assaulting the Bull, with a sword in his belt, and a club in his right hand. It contains two stars of the first magnitude, four of the second, three of the third, and fifteen of the fourth. Be. 4epae forms the right, and Bellatriz the left slloulder. A cluster of small stars forms the head. Three small' stars, forming a straight lioe about 3 0 in length, constitute the belt, called by Job" the BantU of Orion." They are sometimes called the TAree Kifl6a, because they point out the Hyades and Pleiades on the one hand, and Sirius on the other. A row of very small stars runs down from ihe belt, forming the BUJord. These, with the stars of the belt, are sometimes called the Ell and Yard. Mintika, the northernmost star in the belt, is less than lOsouth of the equinoctial. Rigel, a bright star of the first magnitude, is in the left foot, 150 south of Bellatrix; and SaipA, of the third magnitude, is situated in the right knee, st° east of Cftt18 Rigel.. , (TAe Hare) is direotly south of Orion. It may be known by four stars of the third magnitude, in' the form of an irregular square. Zeta, of the fourth magnitude, is the first star, situated in tbe back, and about 50 south oC Saiph ill Orion. A bout the same distance below Zeta are the four principal stars, in the legs and feet. . · QOL1JMlll (Noah'. Dime) lies about 160 south of Lp.pus 11 contains but four stars,. of which PAaet i~ the brig~t • LBPUI SOV~".!f COBSI'BLUTION'. 171 eat. It lies on the right, a little higher than B8ItJ, the next brightest. This last may be known by a amall star just" east of it. " ERIDAInn]" (The RiDe,. Po) is a large and irregular con- stellation, very difficult to trace. It is 1300 in length, and is divided iDto the NortJ&em and &u.them streams. The former lies between Orion and Cetus, commenoing near Rigel in the foot of Orion, and flowing out westerly in a serpentine course, near 40°, to the Whale.· lies southeast of Orion, and may be readily found by the brilliancy of its priocipal star Siri~. This is the largest of tne Fixed Stars, and is >supposed to be the De~rest to the Solar"" System. . " CANIS MAJOR is a small constellation situated between Canis Major. and the Twills. It has but two principal stars, namely, Procyon of the first magDitude, and Go.. melm of the second. CA.NIS MINOR MONOCEROS (The Unicorn) lies between Canis Major and Canis Minor, with its centre directly south of Procyon. Its largest stars are of ~he fourth magnitude. Three of these are in the head, 30 and 40 apart. has its head near Procyon, and consists' of a number of stars of ordinary brightness.. AlpAard, in the heart, is a star of the" second magnitude, about 15° south. east of the head. It "Is an extensive constellation, extend. ing from east to weat more than 100° •. HYDRA. (The CrOfD) i. !represented as standing upon the tail of Hydra, south of Coma Berenices. It contains but nine visible stars, only three of which are as large as the third magnitude. " CoRVUS ARGO NAVIS (The Ship Argo) is a large and splendid constellation in tne southern hemisphere, but so low down in the south that but little of it can be seen in the United States. It lies southeast 0(. Canis Major, aod may b8 kDU"D by the stars in the prow of the ship. Markell, of the third Jnagnitude, is 16° "southealJt of Siriul. NOM .ad \ 180 D011BI&, UJ1tLB, .um MVLTJPLB ST.lBS. ~ are of the second magnitude, and Ct.opu and _iapI,tJeitlu of the first. CBXTAUBUS is another large southem constellation, too low in the 80utb to be traced by an observer in the United States. Lvpus (The Woy) is next east of Centaurus, south of Libra, and is also IDvisible in northern latitudes. (The Seztaflt) consists or a number of very lIIIall stars, situated between Leo on the north, and Hydr. 00 the south. Its largest star is of the fourth magnitude, and is situated about 18° south of Regulus, Dear the eq uiooctial. C.ux (The C1W8) is a brilliant little constellation, but too Car south to be visible to us at the north. It coosists of four prinoipal stars, namely, ODe of the firat, two of the I8OODd, and one of the third magnitude. • SBXTANS CHAPTER II. or DOUBLE, VARIABLE, AND TEMPORARY STABII. BINARY SYSTEMS, &c. Lesson or DOUBLE, 1~4. TRIPLB, AND K11LTIPLB STA... (Map 16.) 1. MARY of the stars which, to the naked ~ye~ appear lingle, are found, when examined by' the aid of a telescope, to OOllsist of two or more 8tars, in a state of near proxjmity to each other. Theee are called tltmble 8t4r.. When three or more 8tare are found thus olosely connect. l , the, . are called 'ripk or ",.ltiple stare. They are al80 iistio. guiahed as 1IirJtzrr, ttmuJry, &c. 2 •. Double aDd triple stars are lupposed to be consti. tuted in two ways: first, by actual ooDtiguity; and aN- DOlJ'BLB, TRIPLE, AND XVLTIPLB STARS. # 181 ondly, where they are only neB.r the same line. of vision, one of the component stars being far beyond the Qther. In the former case they are said to be physically double, from the belief that they are bound together by attraction, and that one revolves around the other, while in the latter case they are considered as only uptically double. Upon this subject Dr. Herschel remarks, that this near• . ness of the stars to each other, in certain oases might ~ attributed to some accidental cause, ~id it oocur o~ly in a taw instanoes; but ·the freq ueilcy of this comp'aniollship., the extreme closeness, and, in many oases,· the near ~qua1ity of the stars so oonjoined, would alone lead to a strong suspicion of a more near and intimate relation than mere casual juxtaposition. · ~ 3. The figures from B to F on the map are speoimens or double stars. B is a representation of the middle star, Misar., in the tail-of the. Great Bear. It may be seen double. with a good spyglass. The stars are both of a greenish white-of the third and fourth magnitudes-and about 141'/ apart. Mizar has sometimes been seen witTi. out a companion, and· at other times it has been known suddenly to appear. 'rhe companion is not .Alcor, near Mizar, and ·visible to the naked eye, but a telescopic 814r. C -is a view of the double star .Mintika, ~n the oonstel. lation Orion. The component stars are of the first and eighth magnitudes, the largest of a reddish hue, and the small Qne white. They are about 10"1 apart, or ,four times the diameter of the largest star. · D is Ii double star in Ur.,a Mincw, . commonly known a8 the Pole 8tar. ft consists of a star of the second and . an~ther of the ninth magnitude, situated about 181'/ apart; or about four times the diameter of the larger star. They are both of a silvery white. It requires a pretty good telescope to show this sta r dou~le, henoe it is considered a pretty good teat ob. 7pet, by observing which to ascertain the qualities of un optical instrument, especially of the low-priced refrac. tol"S. ' E is a view of the double star Castor in the twius. 16 182 OF BINA.,y AND OTHBH. SYSTBJ(S. The stars are of a greenish color, of the third and fourth magnitudes, and about 5", or two diameters of the principal star, apart. This also is considered a good test object. Through ordinary telescopes the stars seerD to be in contact, but with those higher power they appear r:ly divided. These stars also constitute a binary system. The stars under F are specimens of other distances and combinations of magnitudes. 4. The number of double stars has been .variously esti. mated. Sir William' Herschel enumerates upwards of five hundred, the individuals of which are within 80" each other. Profe880r Struve of Dorpat estimated th~ number at about three thousand, and more recent observations fix the number at not lees than six thousand. The great number of the double Itars first led astronomers to suspect a physical connection by the laws of gravitation, and also a reoolutiora of star around star, 88 the planets revolve around the IUD. . . or rai or Lessen 1~3. OF BllfAJLY AKD OTUK SYSTBKS. (Map 16.) 1. By carefully noting the relative distances and angular positions of double and multiple stars, for a aeries of years, it has been found that many of them have their ppriodic revolutions around each other. Where two stars are found in a state of revolution about a common centre, they constitute what is called a Binary SYBteff&. Thp.ae, it must bf' remembered, are the double and multiple stars, which appi'A.r single to the naked eye. Sir W. Herschel noticed about fifty instances of changes in the angular ~sition of double stars, and the revolution of some 8i:I:tem of these is considered certain. Their periods vary from 40 to 1200 years. 2. The star Xi, in the left bind paw of UrBa Major, iR one of thp.se stellar systems. The revol ution of its compon~nt stars' began to be noticed in 1781, siuc~ 1 I • OF BINARY AND OTBBR SYSTBMS. 183 which time they have made one complete revolution, and are now (1847) some eight y'ears OD the second. Of oourse, then, their periodic time is about fiftyeight years. ~heir angular motion is about 60 24" per year. Dr. Dick supposes these stars to be some 200,000,000,000 miles apart; and upon the supposition that the smaller revol ves around the latter, computes its velocity to be not less than 2,471,000 miles every hour. This would be 85 times the veloci.ty of Jupiter, and 23 times the velocity at Mercury-the swiftest planet in the Solar System. 3. :Fig. G on the map is a representation of another of these binary systems. It consists of the double star Gamma, in the Virgin. This star has been known as a double stJlr for at least 130 years. l'he two stars ,re both of the third magnitude, and of a yell<?wish color. The largest star will be seen in the upper foci of the su pposed orbit, and the arrows show the direction of the re. vol ving star. A t the first observation, by Bradley J in 1719, the smallest star was near the lower arrow t 8. represented. In 1766 it occupied a very different position, as the drawing shows, and 80 on to 1844, as repre. aented ~n the map. The period assigned to this system by Dr. Herschel is 829 years. The late E. P. Mason, of Yale College, estimated its period at 171 years: more reoent observations and estimates by Madler, give a period of 145 years. 4. Fig. H is a view of another of these systems of re. volving 8ta~ namely, the double star p, or 70 of the Ser. pent.bearer. In 1780 the smaller star was seen on the right, just above the lower 'arrow. In 1804 it was near that date on the map; in 1822, it was nearly opposite the first position, and 80 on to 1843. The periodic time of' the revolving star is about 93 years. In the course of its revolution the two stara 8Om~times appear separated, sometimes very near to. gether, and at other times as one star. They are of, the 5th and 6th magllitudes, and of a yellowish hue. The following table shows the periodic times, &c., ~ese Binary Systems, 80 Car as known. It is copied from or 184 or B",.£aT AND OTBBJI. SYSTDI. Hersohel'. Treatiae, and corrected where more reoem obaenatiooa have shown it to be erroneous. NUDeI. i Penod in year.. J I CoronE, 43.40 55.00 Caneri, 58.26 U ram Majoris, 93.00 70 Ophiuchi, 452.00 61 Cygni, 252.66 r Virginilll, 286.00 Castor, 145.00 d CoronE, 1200.00 r Leonia, 'I I lIajor axil of i .. J t~e orbit. Eecentnclt,.. I 7N.714 8.784 24.000 16.172 7.358 30.860 0.4164 0.4667 0.8335 0.7"582 0.6112 I I 5. The atudeDt should here be reminded that these are oot .Yltema of plaoef.l revolving around suns, but of ... refHJZfli"K tlrou'ltll ft.; and that their component stars may not only be as far apart as our SUD and Sirius, but that they are probably each the ceotre of his own planetary system, like that which revolves around our eentral orb. Speaking of these .Y8tems. Dr. Dick observes: " To some minds, Bot accustomed to deep reflectioo, it may appear a 'Yery trivial fact to behold a small and scarcely distinguishable point of light immediately adjacent to a larger star, and to be informed that this lucid point revolves around its larger attendant; but this phenomenon, minute and trivial as it may at first sight appear, proclaims the astonishing fact, that SUNS REVOLVB AROUND SUNS, AND SYSTEMS ABOUND SYSTEMS. This is a comparatively new idea, derived from our late sidereal investigatioos, and forma one of the most sublime conceptions which the modem discoveries of astronomy have imparted. It undoubtedly conveys a very sublime idea, to contemplate such a globe as the planet J upiter-a body thirteen hundred times larger than theearth-revolving a round [he 8un, at the rate of twenty.nine thouIUld mile. every hour; and the planet Saturn, with i. OF BINARY AND OTHER SYSTEMS. 185 rings and D1OODS, revolving in a similar mat:ner round this central orb in an orbit five thousand six hundred and ninety millions of miles in oircumference. But how much more august a.nd overpowering the conception of a aun revolving around another sun--of a sun encircled with a retinue of huge planetary bodies, all in rapid m0tion, revolviDg round a distant sun, over a oircumference a hundred times larger than what has been now stated, and ~ith a velocity perhaps a hundred times greater than _that of either Jupiter or Saturn, and oarrying all its planets, satell ites, comets, or other globes along with it in its swift career! Such a SUD, too, may as far exceed these planets in size as our 8un transcends in magnitude either this earth or the planet Venus, the bulk of anyone of whioh scaroely amounts to the thirteen .. hundred.thou. sandth part of the solar orb which enlightens our day. The further W~ advanoe in our explorations of the distant regions of space, and the more minute and specific our investigations are, the more august and astonishing are the scenes which open to our view, and the more elevated do ·our conceptions become of the grandeur of that AI. Inighty Being who' Dlarshalled all the starry hosts,' and of the multiplicity and variety of arrangements he has introduced into his vast creation. And this consideration ~ught to serve as an argument to· every rational being,' both in Ii scientific and a religious point of view, to stirn. ulate him to a study of the operations of the Most High, who is 'wonderful in couDsel ~nd excellent in working,' and whose works in every part ClC his dominions adum. brate the glory of his perfections, and proclaim the depths of his wisdom and the greatness of his power." 6. Ilesides the revolutions of these double stars around each other, they are found to have a proper motion together in space, like that which our sun has around the great Central Sun. Upon this subject Sir John Herschel observes, that these stars not only revolve around each other, or about their common centr~ of gravityJ but that they are also transferred, without parting company, by a progressive motion common to bo~h, towards some deter- minate region. 1 186 OF BDlny .&IfD O'tUB SYSTEIIS. " For example, tbe two staIB or 61 Cygni, which .,. nearly equal, have remained constantly at the same, or very Dearly the same distance, or 15", Cor at least fifty yean put. Meanwhile they have shifted their local sit. uation in the heayenB, in this interyal of time, through DO lese than 41 23", the annual proper motion or each star being 6'/.3; by which quantity (exceediDg a third of their inlenal) this system is every year carried bodily along iD BOrne unknown path, by a motion which, for many centuries, must be regarded as unifonn and recti. linear. Among stars not double, and DO way differing (rom tbe rest in anyotheE obvious· particular, ,. Cassiapeim is to be remarked as having the greatest proper wo. tion of any yet ascertaioed, amounting to 3".74 of annual displacement. And a great many others have been observed to be thus constantly carried away from their places by smaller, but Dot less unequivocal motions. " Motions which require whole centuries to accumulate before they prod uce changes of arrangement, such as the naked eye can detect, though quite sufficient to destroy that idea of mathematical fixity which precludes specula. tion, are yet too trifling, 88 far as pra.ctica~ applications go, to induce a change of language, and lead us to speak of the stars in common parlance as otherwise than fixed. Too little is yet known of their amount and directioDs, to allow of any attempt at referring them to definite la WI. lt may, however, be stated generally, that their apparent directions are various, and seem to have no marked com. mon tendency to one point more than to another of the heavens. It was, indeed, supposed by Sir William Her. achel, that such a oommon tendency could be made out; and that, allowing for individual deviation8, a general receS8 could be perceived in the principal stars, jrOJll. that point ocoupied by the star { Herculis, I!nDaTtU a point diametrically opposite. This general tendency was re. ferred by him to a motion of the sun and solar system in the opposite direction. No ODe, who reflects with due at. tention on the subject, will be inclined to deny the high probability, Day, certainty, that the SUD htu a proper mo. tion in 80me direction; and the inevitable oonseq uence of .1 . ~ 187 O' B1!4AB.Y A.N.1) OTHER SYSTEMS. 8uch a motion, un participated by the rest, must be a slow tlOBra,ge apparent tendency of all the stars to the vanish. iog point of lines parallel to that direction, and to the region which he is leaving."· .. 7. As already stated in a previoU8 188800, m,any of the double, triple, and multiple stars are of "ariofU COM', beautifully contrasting with each other. fC _ _ _ _. other SUDS, perhaps, :With their attendant moons , Communicating male and female light, (Which two great sexes animate the world,) Stored in each orb, pt'rhapa, with lOme that live."t "In such instances, the larger star is usually of a ruddy or orange bue, while the smaller one appears blue or green, probably in virtue of that general law of optics, which provides that wben the retina is under the influ. ence of excitement by any bright-colored lights, feebler lights, which seen alone w.ould produce no sensation but of whitf'ness, shaU.J9T the time appear colored with the _tint complementary 'to that of the brighter. Thus, a yel.. low color predominating in the' light of the brighter star, that of the less bright one in the same field of view will appear blue; while, if the, tint of the brighter star verge to crimson, that of the other will exhibit 8 tend~ncy to green--or even appear as a vivid green, under favorable circumstances. The former contrast is beautifully ex. hibited by. Cancri-the'latter by r Andromedm; both fine double stara. If, however, the colored star be much the less bright of the two, it will not materially affect the other. Thus, for instance, 'J Ca~iopeim exhibits the beautiful combination of a large white star, and a small one of a rich ruddy purple. It i$ by no means, however, intended to say, that in all such cases one of the colors is a' mere effect ~f contrast, and it may be easier luggested in words than conceived in imagination, what variety of illumination t'IDO BUnS-a red and a green, or a t <. .-------------------------------------------• Sir Johu Henchel'. Treati8e OD AaboDOlDJ. t Paradile Lo.i, 'YiiL, 148. • '. 188 v A&UBLB 0& PB&IODICAL STA )l.S. yellow and a blue one--must aff'oN a planet cir~ulating about either; and what charming contrasts and 'grateful vicissitudes'-a red and a green day, for instance, alternating with a white one and with 4arkness-might arise from" the presence or absence of one or oth~r, or both, above the horizon. Insulated stars of a red color, almost u deep as that of blood, ocour in many parts of the beav., eDS, but no green or blue star (of any decided hue) has,· we believe, ever been noticed un associated with a com. panion brighter than itself."* Lesson 1~6. V ARIABLB 0)1. PB)l.IODICAL STAlLS. 1. Variable stars are those which undergo a regular periodical increase and diminution or lustre, am.ouoting, ID some cases, to a complete extinction and revival. These variations of brilliancy, to which some of the fixed stars are subject, are reckoned among the m081 remarkable of the celestial phenomena. Some oC .them pass through their successive changes with great rapidity, while in other cases their brilliancy is increased or diminished gradually for months. The time" occupied by one of these stars, in passillg through all their different phases, is called its period. 2. One of the most remarkable or these variable stars, is the star Omicron, or Mira in the Whale. I ts period is about 332 days, during which time it varies from a star the second magnitude, to complete invisibility. It appears about twel va times in eleven years-remains at its greatest brightness about a fortnight, being then, 00 lOme occasions, eq ual to a large star of the second magnitude. It then decreases for about three months, wheo it disappears. In about five months it becomes visible again, and continues to increase during the remaining three months of its period. Its increaSe of light is much more rapid than ita or • Sir John HellChel'. Tleame - A.a.om,. VAIUABLB OR PBa:ODICAL IT.lBS. 189 decrease. It increases from the sixth to the second magnitude in 40 days-continues thus brillia.nt jl6 days, and then fades to the sixth magnitude again in 66 days. Hence, it is above the sixth magnitude for 182 days, and below 200 days of its pe'riod. 3. Another remarkable periodic star is that called Algol, in the constellation Per8eua. It is usually visible as a star of the second magnitude, and such it continues for the space of 2 days 14 hours~ when it suddenly begina to diminish in splendor, and in about 3! hours it is red uced to the fourth magnitude. It then begins again to increase, and in 3l hours lDore is restored to its usual brightness, going through all its changes in 2 days 20 hou rs and 48 minutes, or thereabouts. Through all its successive changes, this star shines with a white light, while the color of all the other variable stars is red. 4. The cafUB of these' periodic variations in the brightness of soml\ .)f the stars is not known. Some suppose them to be occasioned by opaque bodies revolving aroul'd them, and cutting off a portion of their light from u •• ,Speaking of the sudden obscuration of Algol, mentioned above, Dr. Herschel remarks, that it indicates a high degree of' activity in regions where, but for such evidences, we might conclude all lifeless. " I am disposed," says Dr. Dick, "to consider it as highly probable, that the· in. terposition of the opaque bodies of large planets revolving around stich stars, may, in some cases, account for the phenomena. It is true, that the planets connected with the Solar System are 80 small, in comparison of the SUD, that their interposition between that orb and a spectatf?r at an immense distance, would produce DO sensible effect. But we have no reason to conclude, that in all other systems the planets are formed in the same proportions to their central orbs as ours; but, from the variety we perceive in every part of nature, both in heaven and earth, we have reason to conclude that every system of the universe is, in some respects, different from another. There is no improbability in admitting, that the planets which revolve round some of the stars, may be so large as to lK"" a coDsiderable proportipn 190 V..a'A BLa oa PUIODICAL ITAal. (perhaps one.half or one-third) to the dfametera of the orbs around which they revolve; in which case, if tbe plane of their orbit lay nearly in a line of our own vi8ion, they would, in certain parts of thQir revoluti~ns, interpose between our eye and the stars, so as to hide for a time a portion of their surfaces from our view while in that part of their orbits which is next to the earth. " With reference to the obscuration and period of Algol, Professor Olmsted observes, that the periodic time of an ovaque revolving body, 8uffi'Ciently large, which would produce a similar temporary obscuration of the 8un, seen from a fixed atar, would be less than fourteen hours. Others again are of opinion that those distant suns have one luminous and one dark or clouded hemisphere, and that their variations may thus .. result from a revolution upon their axes, by which "they would present us alternately with their full and their diminished lustre. A nother theory is, that these stars are moving with inconoeivable velocity in an immensely elliptical orbit, the longer axis of which is nearly in a direction to the eye; and the shorter axis of which would be imperceptible from our system. In such case the star would appear alternately to approach and recede, now looking in upon our quarter of the universe, as it were, for a few days, and then rushing back into immensity, to be seen no more by human eyes during the lapse of years or of ages. " Whatever may be the causs," says Mr. Abbott, "the fact of these variations is perfectly established, and the contemplation of the stupendous changes which must be occurring in those distant orbs, overwhelms the mind with amazement. Worlds vastly 18 rger than our sun sudden. ly appear, and as suddenly disappear-now they blaze forth with most resplendent brilliancy, and again they fade a \vay-and .often are apparently blotted from existence. These worlds are unquestionably thronged with myriads of inhabitants; and the phenomenon which to us appears but as the waxing or waning lustre of a twinkling star, may, to the dwellers on these orbs, be evolutions of grandeur, sucb as DO earthly imagination . -- TBJlPOBAKY ITAB,S. 191 bas ever conceived. But these scenes, DOW Teilecl from human eyes, will doubtle. all be revealed, when the Christian shall ascend on an angel's wing to the aDgel'. home." Lesson 1117• TEMPOllA.llY STABS. 1. Temporary stars are those which have appeared - from time to time, in different parts of the heavens, blazing forth with extraordinary lustre, and after remaining tor a while apparently immoveable, died away, and left no traces of their existence behind. Some writers cl_ them among the Periodical Stars, while others notice them under the head of " New and Lost Stars." " 2. A star of this kind, which appeared in the ye.ar 125 B. led Hipparchus to draw up a catalogue of the IItarl, tbe earliest on record. In A. D. S89, a similar star appeared Dear the largest star in the Eagle, which, after temaining for three weeks 88 bright as Venus, disappeared entire} y from view. 3. On the 11th of November, 1572, Tycho Brahe, a oelebrated Danish astronomer, was retu~ning in the eveDing from bi. laboratory to hie dwelling~house, when he was surprised to find a group of couotry-people gazing upon a star which be was sure did not exist half an hour before. It wal then as bright as Sirius, and continued to increase till it surpa.ed Jupiter in brightness, and was visible at noonday. In December of the same year :it began to dimillish, aDd in March, 1574, had entirely diaappeared. This remarkable star was in the constellation Ca88i.o. IMia, about 60 northeast of. the star Cap". The pluce where it once shone is now a dark void! This star was observed . for about sixteen lllootbs, and .during the time of its visibility its· color exhibited all the dift'erent shades of a prodigious fiame-" first it was of a dazzling white, then of a reddish yellow, and lastly of an ashy paleness, in whioh ita light expired." "It is im. c., ------- 192 TDPPIl.A.llY STARS. possible," says Mrs. Sumerville, "to imagine any tbi. more tremendous than a conflagration that could be visible at such a distance." In reference· to the same phenomenon, Dr. Dick 01>-I8nes, that" the splendor concentrated in that point the heavens where the star appeared, must have been, in reality, more thaD equal to the blaze of twelve hundred thousand worlds such as ours, were they all colleoted into one mass, and all at once wrapped in flames. Nay, it is Dot improbable, that were a globe as large as would ill the whole circumference of the earth's annual orbit, to be lighted up with a splendor similar to that of the 8un, it would scarcely surpass in brilliancy and splendor the star to which we refer." The same writer observes, that" within the last ceolury, no le~ than thirteNJ stars in different constellatioll8 .aem to have totally perished, and ten new ones to have been oreated." REV. PROFESSOR VINCE, who been characterized lUI "one 'of the most learned and pious astronomers of the age," advances the opinion that "the di~appearance (-f lOme stars may be the destruction of that system at the time appointed by the for the probation of its illhabitants; and tbe appe~rance of new stars may be the! formation of Dew systems for new races of beings than called into exiltence to adom the works of their Crea- or haa n,rrY tQr." L.A.. PLA.CE, whose opinion upon such subjects is always entitled to consideration, says: "As to these stars which luddenly shine forth with a very vivid light, and then im- . mediately disappear, it is extremely probable that great conflagrations, produced by extraordinary causes, take place on their surface. This conjeoture is confirmed by their change of oolor, which is analogous to that presented to us on the earth by those bodies which are set OD fire and then gradually extinguished." DR. GOODB, author of the Book of Nature, &0., seelDfl to have entertained an opin~on similar to those already expressed. "Worlds and systems of worlds," says he, "are Dot only perpetually 9reating, but al80 perpetual}, , -.., PALLING OR SBOQTING nABS. 193 disappearing. It is an extraordinary fact, that within the period of the last century, not less than tAimen ,tar., in different constellations, seem to have totally perished, and ~ fle1D onea to have been oreated. In many instances it is unquestionable, that the stars themselves, the supposed habitations of other kinds or orders of intelligent beings, .together with the different planets by which it is probable they were surrounded, ha va utterly vanished; and the spots they ocoupied in the !teavens have become blanks. What has befallen other systems, will assuredly befall our own. Of the titTLe and manner we know noth. ing, but the fact is incontrovertible; it is foretold by revelation; it is inscribe{f in the heavens; it is felt Ithrough the earth; such is the awful and daily text. What then ought to be the comment 1" ~ Lesson 1118. I • J I PALLING OR SHOOTING STARS. The subject of shooting stars is here introduced, not because it properly belongs here, by the laws of philosophical classification, but because the juvenile student will be more apt to look for it in this connection than in any other part ot the work. We must say but little, however, as its full discussion falls not within the compus of our design. . 1. Falling or shooting stars are not properly 614r., of any kind, but meteor., witllin a sbort distance or the earth. A meteor is a fiery or luminous body fiying through the atmosphere. 2. Although the number of shooting stars observable in a single night is usually small, there have been instances in which they feU in suoh numbers as to be de. nominated Meteoric 8lwwr,. One these occurred November 13th, 1838. On that morning, says Professor Olmsted, from two o'clock until broad daylight, the sky being perfectly serene and cloudless, the "hole heavens were lighted with a magnificent display of celestial fire. works. .At time. the air was filled with streaks of light. or 17 · 194 .- OF CLUSTBB.S OF STA.KS. occasioned by fiery particles darting down 80 swiftly as to leave the impre~ion of their light on the eye, (like a match ignited and whirled before the face,) and drifting to the northwest like flakes of snow driven by the WiDd ; while, at short intervals,· balls of fire, varying in size from minute points to bodies larger than Jupiter and Vonus, and in a few instances as large as" a full moon, descended more slowly along the arch of the sky, often leaving after them long trains of light, which were, in 801ne instances, Tariegated with different prismatic colors.· 3. Of the nature of these meteors very little is known. They are supposed to descend from some point beyond the limits of our atmosphere, and to be ignited by their rapid motion, as they come in contact with it. They explode, and are reerolved into srnaH clouds, it is thought, at the height of about thirty miles above the earth. Professor Olmsted thinks they are caused by some rare body like the tail of a comet, or the zodiacal light, falling in the way of the earth in her annual joumey around the 8UD. CHAPTER III. OF CLUSTERS OF STA.RS, A.ND NEBUL£ Lesson 1~9•. 01' CLUSTERS OF STA.RS. (Map 16.) 1. IN Iu"eying the concave of the h~veD8 in a clear night, we observe bere and there groups Qf stars, forming bright patches, as it d ra WD together by' tlOme cause other tha.n casual distribution. Such are t'he Plri4du and By. in Taurus, the fOrmer of which • Introduction to Astronomy, p. ~ - 1 01' CLt18TBB.S OF STARS. 196 may be aeen at I, on the map. These are called OZUW8 of Star.. 'The constellation Coma Berenice, is another such group, more diffused, and consisting of much larger stars. The luminous spot called the Bee Hi'Oe, in Can. oer, is somewhat similar, but less definite, and requires a moderate telescope to resolve it into stars. In the sword. handle of Perseus, is another such spot or cluster, which req uires a rather better telescope to reSQI ve it into distinct stars. 2. There is a great number of these objects, which have been mistaken for comets, as through telescopes moderate power they appear like the comet of 1585, Map 15, or like small round, or oval, nebulous specks. Sir John Herschel observes that Messier has given a litit of 103 objects of this sort, with which all who search for comets ought to be familiar, to a void being misled by their similarity of appearance. That they are not comets, however, is evident from their fixedness in the heavens, and from the fact that when we come to examine them with instruments of great power, they are perceived to cODsist entirely of stars, crowded together so as to occupy almost a definite outline, and to run up to a blaze of light in the centre, where their condensation is usually the greatest. 3. Many of these olusters are of an exactly round figure, and, convey tbe complete idea a globular space filled full of stars, insulated in the heavens, and constituting in itself a family or society apart from the rest, and lubject ooly to its own intemallaws. 4. It would be a vain effort to attempt to oount the . stars in one of these globular cluste ..s. They are not to be reckoned by hundreds; and on a rough calculation, grounded on the apparent intervals between them at the borders, and the angular diameter the whole group, it would appear ~hat many clusters of this description must contaio" at least from ten to tweoty thousand stars, com. pacted ,and wed2ed together in a round space, whose an. gular diameter does not exceed eight or ten minutes, or an area equal to a tenth part that covered by the· or or or or mooD. 196 OP NBBVU. 5. Some of these clusters are of an irregular figure, as may be seen at J, on the map. These are generally less rich in stars, and especially less condensed towards the centre. They are also less definite in point of outline. In some of them the stars are nearly all of a size, in oth. ers, extremely different. It is no unCODlmon thing to find a very red star, much brighter than the rest, occupying a conspicuous situation in them. 6. It is by no means improbable that the individual lltars of these clusters are suns like our owo, the centres of 80 many distinct systems; and that their mutual distances are equal to those which separate our 8un from the nearest fixed stars. Besides, the round figure of lOme of these groups seems to indicate the existence lOme general bond of union in the nature of an attractive (orce.* 7. Figure J on the map, is a representation of the cluster in Coma Berenices already referred to; and Figure K is a magnificent cluster in Capricornus, containing more than a thousand fixed stars. A cluster of stars, numbering over 1,000, bas recently been. announced as discovered by Professor Mitchel, of the Cincinnati Observatory. or Lesson 130. OF NEBULAS •. (Map 16.) 1. The term NEBt1L.E is 8.pplied to those clusters ata~ that are so distant as to appear only like a faint . cloud or haze of light. In this sense some of the clusters heretofore described may be classed as nebulre, and in. deed it may be said of all the various kinds of nebul." that it is impossible to say where one s~cies ends and another begins. 2. RBSOLVABLE NEBUL.& are those clusters the light of whose individual stars is blended together, when seeD or , • Bench.I'. Treat. . II 197 through a common telescope, but which, when viewed through glasses of sufficient .power, can be resal ved into distinct stars. S. lUBSOLVABLB NBBUL& are those nebulous spots which were formerly supposed to consist of vast field. of matter in a high state of rarefication, and not of distinct .-tars. But it is exceedingly doubtful whether any nebu.. 1., exist which could not be resolved iDto stars, had we telescopes of sufficient power. The following remarks, taken· from a lecture recently delivered in Dublin, by Dr. Scoresby, in relation to the powers of Lord RoSIe's mammoth telescope, will reflect light upon the subject un. der consideration. "A bout the close of last year, the Earl of Rosse succeeded in getting his great telescope into oomplete operation, and during the first month of his obeervations 00 fifty' of the unresolvable nebulm, he 8Uooeeded in asoertaining that forty-three of ~hem were already resolvable int6 masses of stars. Thus is confirmed the opinion, that we h~ve only to increase the powers of the instrument to resolve all the nebulm into stars, and the grand nebular hypothesis of La Place into a splendid . astronomical dream." In a more recent communication Dr. Scoresby remarks, that the nebulre already observed were belween one and two hundred, which was doing well considering the ob. aervatioDs had often been obstructed by the cloudy nights. Although this great telescope has been erected nearly' two years, it has not been in complete operation more than six or seven months, and already the nebulm, not be. fore fully examined, have been discovered to be a collection of SUDS. From these recent observatioDs it is probable that all the nebulm might be resolved into distinot stars if we had telescopes of suiicient power, and that such an objeot u an irresolvable nebula does not in reality exist. While upon the subject of the nebulre, as viewed by Lord Rosse, we must not omit to notice the extraordinAry spiral nebula, recently discovered by the aid of his mam. moth telescope. The following is the announcement the dilCOvery, u given in the English journala: or 17* 198 . UTIlAOIlDINA.IlY OP NEBULa. SPIB.A.L NEBULA. DISCOVBRBD BY LOU B.OSSB. The Spiral Nebula is situated in the Dog's Ear, and although, by the oommon consent of astronomers, it was considered a mighty 01 uster of stars, it was not until ~rd Roese had seen it by the aid of his six-feet mirror that iii resolution into stara was effected. This wonderful nebula bears closely on a problem relating tQ the structure of our own galuy, the Milky Way. However strong the aympathies pe"ading all that strange system, it is cognizable by U8, in the mean time, only as a collection of leparate masses. N or can we err in so deeming it, through ignoranoe of its real, as compared with its apparent structure, inasmuch as it is the manifest tendency., of the telescope to deprive these remote objects of apparent uniformity, and endow them with a constitutioD more and more discreet. Now, these parts are, by themselves, somewhat intelligible. The central spherical group has the form in which gravity would sustain any mass of stars; and most of the other segregated ponioDl also can be ~onceived as partial schemes internally har. monious, or arranged in obedience to their internal sym. pathies. But the feature the most remarkable for U8 is the character of the two principal lines of the scroll, or those two leading 'branches of that Milky Way where the stars of the group appear mainly distributed. It seems as if these beds of orbs we ra lite rail y di8801 ving into fragments, which, in fact, is only a repetition of the moet conspicuous characteristic of the zone enoircling our own .galaxy; for the bright circuit of our Milky Way is DO regular belt, but,. on the contrary, a suocession of olu8teN, probably self-harmonious, stretching along its whole course, and separated by lines or patohes more or less obscure. Nothing oan be more memorable than the coDversion of these dim streaks of light into burning and rolling orbs: even a feat 80 grand and triumphant, in regard the science and art of man, has an attraotion infinitely less than the tranaforming of a shape apparently simple, or 01' NBBtJL.&. 199 Into ODe 80 strange and complex that there is nothing to which we can liken it, save a scroll gradually uDwinding, or the evolutions of a gigantic shell! How passing mar. venous is this universe! And unquestionably that form would seem stranger still, if, rising farther above the imperfections of human knowledge, we couhlP see it as it really is; if, plunging into its bosom and penetrating to its farther boundaries, we could develop the struoture ot its still obscure nebulosities, which doubtle. are Itreamll aod masses of gorgeous related stars! • . Figure L on the map is a representation of the great Debula in Andromeda, fonnerly considered as irre8Olvable. It resembles a comet, and may be seen under fav~rable circumstances by the naked eye, like a small faint cloud. The stars leen within its limits are supposed to be beyond it, and consequently seen through it. 4. N ebulm are again distinguished as Single and DOUBLB N BBtTL.&. The former consist of one cl ulter aantling alone, while in the latter case two or more seem to be united, or in a state of near proximity, as in Figure M. Of the Double Nebulae there is almost every possible variety of form and proportionate magnitude. The specimen given is a representation of the double nebulm in the Greyhound. 5. Figure N is a representation of what are called HOLLOW NBBULJI. This speoimen may be found in the constellation Sagittariul. 6. STELLAR NBBVL..., or Ne1nilotu Star" are Iuch u present the 'appearance of a thin clolld with a bright star in or Dear the oentre. They are round or oval. shaped, and look like a star with a burr around it, or a candle shining through hom. Figures 0 and P on the map are specimens of this class. 0 is in Cancer, and P . in Gemini. . 7. The SUA is considered by astronomers u belonging to this class of nebulous stars, and the ZodilJClJl Light, 'of which we have spoken in Lesson 108, has been regarded 88 of the nature of the gaseous matter with which the Debulous stars are surrounded. It is supposed thAt if we were as far from the SUD as we are from the Stella, toe OP NmI11L.&. Nebul., he would appear to UI only u a smalL aDd nebulous star ! 8. PLANBTAB.Y NuvL.&, 8ays Dr. H"erschel, are Tety Btraordioary objects. They have, as their name imports, exactly the appearance of planets; round or .lightl y oTal discs, in some instances quite sharply terminated, in others a little hazy at the borders, and of a light exactly equable or only a very little mottled, whioh, in some of them, approaches in vi vidne8S to that of the actual planets. Whatever be their nature, they must be of enormous magnitude. Granting these objects to be equally distant from us with the stars, their real dimeDlions must be such as would fill, on the lowest computa. tion, the whole orbit of Henchel. Fig. Q on the map,- is in&ended as a specimen or Planetary N abulm, though, it must be confessed, it is not easy to get up a very striking resemblance. 9. ANNULA.B NBBUL.& alao exist, but are seldom to be met with. The most conspicuous of this class is to be found exactly half. way between Beta and &4"","" in the Lyre, and may be seen with a telescope of moderate power. It is small, and particularly wall defined, 80 88 ID fact to have much more the appearance of a flat oval aolid ring than of a nebula. The space within the ring Is filled with a faint hazy light, uniformly ~pread over it, like a fine gauze stretched over a hoop.10. Figure R is a representation of a very remark. able nebula in the head of the Greyhound, about six degrees below Mizar, the middle star in the tail of the Great Bear. I t consists of a large and bright globular nebula 8urrouDd~d by a double ring, at a considerable distance from the globe, or rather a single riQg divided through about two-fifths of its oircumference, and having one portion turned up, as it were, out of the plane of the rest. A faint nebulou8 atmosphere, and a small round nebula near\it, like a satellite, completes the figure. 11. Figure S is another remarkable nebula in the OODstellatioD or the Fox. The two round spots about tile . • Sir J. BencheL OJ' NBBVL.&. 201 foci of the ellipee or oval, exhibit b~t a (aint and dusky light, while the portioDS about the ends of the sborter axis are remarkably bright and uniform. 12. Figure T represents a wonderful nebula in the Milky Way. Its form is fantastic, and it has several openings, through which, as through a window, we seem to get a glimpse of other heavens, and brighter regiona beyond .. 13. The "uIIINr of nebulo1;1s· bodies is unknown, per. haps we' should say innumerable. They are especially abundant in the Galiuyor Milky Way. Sir W. Her. ache) arranged a catalogue showing the places of ,., Uatnuand of these objects. They are of all shapes and sizes, and of all degrees of brig~tnes8, from .the faintest milky appearallce to the light of a fixed star. 14. Star Dust is a name given to those exceedingly faint nebulous patohes that appear to be scattered about at random in the far.distant heavens. They have DO definite boundary, and are well represented by the grfJg portions of the map, between the various speoimens of nebulm. The map is printed light or gray on purpose to furnish specimens of Star Dust, or of nebulm 80 remote as to be barely visible through the best telescope.. This olass of nebulous appearanoes seems to lie in the back. ground, far beyond others that are more distinctly visibl~ By placing the learner at a proper distance (rom the map, the idea we wish to convey will be readily under.. , • 000. to. This map may be used to very good advantage to illustrate the uses and powers of the. telescope, in re. IIOlving oebullB into stars. Place the pupil at the distance of from fifteen to twenty feet, according to the strength of the light, so that he will see the clusters J and K only as faint oloudy patches. Let him then make what he may call a telescope of low power, by rolling up a sheet of paper, and looking through the tube thul formed., Shutting the surrounding light from his eye will enable him to see the nebulous spots far more dis. tinctly. 'fhen, instead of a telescope of higber power, let hbn approach balf way to the map, and look agaill . • • 202 OF . . . . . . . through his paper tube. IC the light is good, J and It will be moaIy reaolved into atara. By approaching still Dearer, more stars will be I8eD wbere it appeared nebu10118 befbre, and at leogth the &.r Dut will be seeD 11iD8 beyood the more djstinct nebube, in remote regiODII or_pace. It muat not be supposed, however, tbat barely shutting the surrounding light (rom the eye is the principle upon which the teleaoope reveals objects othenriae invisible; the object in these ezerciseB is merely to show that 88 the nearer we are to an object the more distinct the vision, 10 the beuer the telescope (an instrument which seems to bring objeota towards us) the more perfect the view we have of the durareDt kinds of nebulae, and the more likely they are to be reeolved into distinct stars. 16. The nebulm, says Sir John Herschel, furnish in every point of view an inexhaustible field oC speculation ad conjecture. That by Car a larger share of them COD· m.t of stars, there can be little doubt; and in the inter. minable range of system upon system, and firmament upon firmament, which we 1hua catch a glimpse of, the imagination is bewildered and lost. , 17. The Milky Way is generally regarded byastrono. men u only a specimen of nebulm, of which our sun is ODe of the &tall. This zone of Hlnall stars (for such it actually is) extends quite around the Solar System, as the Debulqus circle oC Figure R, on the map, extends around the large Itar in the centre. Like that circle, also, the Milky Way is divided through. some part of its circuit, and bu various branches and irregularities. The vast apparent ~t of the Galaxy, as compared with other nehulm,_ is supposed to be justly attributable to its comparative Were we al rar from the Solar System as we ~re from the nebula in the Lyre, Fig. R, the Milky W~y would doubtless appear as aD Annular Nebula no larger than that. It may therefore with pro~riety be called "the Great Nebula of the Solar System.' The general ooDclusioDI of Midler respeoting the COD. ltitution of the whole Iystem Qf the hed stars, Roluaivi I taearrle,.. • OF NEBUL.E. 203 , distant nebulm, are the following :-He believes that the middle is indicated by a very rich group, (the or the Pleiades,) containing many considerable individual bodies, ~ough at immense distanoes (rom U8. Round this he supposes that there is a zone, proportionally poor in stars, and then a broad, rich, ring-formed layer, followed by an • "'lerval comparatively devoid of stars, and afterwards by another annular and starry space, perhaps with several alternations of the same kind, the, two outmost rings com. posing the two parts of the Milky Way, which are COD· founded with each other by perspective in the portions most dis~ant from ourselves. But what an idea is here conveyed to the mind of the almost boundless extent of the Universe! Sir W. Her. schel estimated that 50,000 stars passed the field of his telesoope, in the Milky Way, in a single hour! And yet the space thus examined was hardly a point in this great zone of the "sun-strown firmament." The mutual distances of these innumerable orbs are probably not le88 than the distance from our sun to the nearest fixed stars, while they are each the centre of a distinct system worlds, to which they dispense light and heat. Were the Universe limited to the Great Solar Nebula, it would be impossible to conceive of its almost infinite dimensions; but when we reflect that this vast and glowing zone of suns is but one of thousands of such assem. blages, which, from their remoteness, appear only as fleecy clouds hovering over the frontiers of space, we are absolutely overwhehned and lost in the mighty aby~ of being! And here we may leave the reader to his own reflec. tions. While unnumbered worlds and systems of worlds glow before his vision in the distant heavens, peoplin,z, as it were, every portion of the mighty void, let it not be for. gotten that as productions of the great Architect" these are but parts of his ways." While he upholds them aU "by the word of his power," and presides over them 88 the GREAT KING, the falling sparrow attracts his notice, and the very hairs of our heads, are numbered. And· while we behold his Wisdom, Power, and Goodness If) or 204 OF KBIJUL.&. gloriously inscribed in the heavens, let us learn to be humble and obedient, to love and serve our Maker here, that we may be prepared for the more extended scenes oC another life, and for the aociety of the wise and -goQd in a world to eome. . ~ APPENDIX. Aberration, an apparent ch~nge of place in the 8tars, which ariaee (rom the motion fixeel or the earth combined with the motion of light. AcMnuJr, a fixed star of the first magnitude, in the CODstellation ErUlaft..., B. A.. 1 bour 31 minutea.-Dec. 58 degrees, 16j- minutes• .Achromatic, oolorl888, remedying aberrations of color. Aclwo,&ieal rising or letting of a planet, or star, is whNI it rises at 8unset, or lets at sunrise. Aerolitu, or air.stones, are semi-metallic Iubstanoee, which are found to faU (rom the atmosphere in different countries. Some philOlOphers have imagined that they are the fragments of a planet that had beeD burst asunder. ~ . . . .A~baratl, a fixed star of the first magnitude in the ... bead of the constellation Taurus; sometimea called the Bal(. eye. AIfol, a star in Medusa's bead, which varies from the I8COm to the fourth magnitude. . Aliat/a, a fixed star in the tail of the Great Bear. AlttJir, a star of the fint magnitude in Aquila. AltitwJ,e, the height of the 8UD, mOOD, or stars aboTe the horizon, reckoned in degrees and minutes, OD a verti. cal circle. ~ mpAUcii, a Dame giTeD to the inbabitants of the torrid • .Th. Gla.ary • copied ,lorn English worb Jatel, reprinted ia tlli. CODay. and reviled 'to adapt it to the capacity of the JuyeDile Leamer. The z."guage of the definitioD8 ii, iD IIOID8 iJultanc., dif. fenat from that UIed in the precediDg papa, and a lew tel'lDll are iDIerted aad defined that do DOt occur in aDY of the 181l0III. But theae circolDltancel will rather eDhance than depreciate ita niue, u they aecure an agreeable yariety where the meaning iI the ame ; wiD ..tt~ulate the IDYeaigatioD of eubjecta not yet 1lDclenIoocI; aad mat . . . . to adcIi&ioDal I.earch in fields Dot yet ezplo:ed. 1;~ 206 APPBN'DlX. zone, on aooount or their shadows falling at one time of the year towards the south, and at another time towards the north. . Amplil:ude, an of the horizon, contained between the-east or west point of the heavens, and the centre of the sun or a star, at the time of its rising or setting• .Arulronaetla, a female, a northern oo~~eUatioD, containing 66 Itars. AntlaU"', a ring.-Anau.,rioga.-AMulGr, ring-like. AfIOfIUIlou, irregular, 8trange, out of rule. . Anomaly, (the true,) the distance of a planet in signs, degrees, &0., from that point of its orbit which is furthest Crom the .un. The mean anomaly is, that which would take place if the planet moved uniformly in the circum.. ference of a circle. AntiR0U8, the Youth, a part of the constellation Aq nila. Antipode., those inhabitants of the earth who live dia. metrically oppoeitq to each other, or walk feet to feet, on opposite sides of the globe. Ant6eci, • Dame given to thOll8 inhabitants of the earth . who Ii ve under the same meridian, aDd at equal distances from the equator, but OD oppoGte sides of it. ApAeliOft, that point in the orbit of a planet in which it is at its greatest di8tance from the sun. Apogt" that point in whicb the lun, or a nlanet, is fur. thest distant from the earth. Appr~mtJte, next, near, approaching. . . Apsidu, the two most remote points of a planet's orbit, otherwise termed its aphelion and perihelion. A line joining those pointe is, the line of the apsides. Arcticu, a star of the first magnitude in the Great Bear. ..drcturu, a bright atar of the ii.rat ,magnitude in the arc constellation Bootes. Armiliary.-rp1aere, an instrument composed or the prine ciprrl circles which are drawn on an artificial globe • .Ascii, the inhabitants of the torrid zone; so called, be. cause the sun being twice a yea r in their zenith, their bodies at those times cast no shadow. Aapect, situation of the stars with respect to one an. otber, or the planeUJ. I • APPBNDIX • 207 .AsteroitU,the eight planets lately discovered moving in eccentric circles between the orbits of Mars and Jupiter. A8tronor11y, (trom A.tler, a star, and Nome" a law,) the science which teaches the motion, magnitude, and distances of the heavenly bodies. A.ttraction, that inherent principle of matter by which bodies mutually tend towards each other, or to the centre of the earth. . Am, (aze.t, plural,) of the earth or of a planet; an imaginary line passing through the centre from one pole to another, round which they perform their diurnal rotation. Azimutu, great circles which pass through the zenitb and Dadir, perpendicular to the horizon. The azimuth a celestial body is an arc or the horizon contained be. tween the east and west points, and a vertical circle pa•• iog through the centre of that object. . or Bellatriz, a star in Orion. Belt., zones surrounding the body ot Jupiter and Saturn. Bet.elgue,e, a star in Orion. Binary, double, consistin~ of two. Bi88eztile, (or leap year,) which alappens every fourth year, and contains 866 days; one· day being added to the • month of February. Capella, a star of the first magnitude in Auriga. Cardinal puint. of the compass; the east, west, north, and south points. Cardinal poin" of the ecliptic; the first points of the signs Aries, Cancer, Libra, and Capricorn. Castor, one of the Twins, a star of the first magnitude in Gemini. Cenlauri, the Centaur, (half man and half beast,) a southem constellation. Centrifugal fOrce, that (orce by which any revolving body eDdeavors to fly off from the centre of motion in a tangent to the circle it describes. CentripetalfMce, the tendenoy which a body has to the centre of its revolution. Circumpolar, signifying such stars. as being near the 208 UPDDI%. pole, moTe aroand it. They eet below the horizon in our latitude. • Col.,.u, two imaginary ~ircles, or meridi8D8, one or which palSBli through the solstitial points Canoer and Capricorn, aDd the other through the equinoctial pointa Ariee and Libra. COtIIeU, erratic bodies belouging to our system, which move round the BUD in very eccentric orbits, distinguished by their fiery tails and nebulous upeets. Ccnae, a body with a circular hue declining to a point, like a sugar-loaf. Ctmical, form of a cone. Conjuru;timt, is when two or more stan, or planets, are in the same part of the heavens. C.OfI8IellatiorJ" or .A.sterism, certain figures delineated in the heaveDs by the ancients, and also by the modems, within which the principal stars are included for the pur. plI8 of better finding and describing them. COII8titueftU, ~rts composing and essential to the whole. Conni,cal rising or setting of a planet, or stal, is when it rises with the sun in the morning, or IJets with him in the evening. Cry8talline 1ae4"tm8, the solid spheres by means of which the ancients attempted to account for the apparent motioD8 the fixed stars. : Cuap8, the .points or horns of the o)oon or of a planet. Cycle of t1uJ moon, Ii revolution of nineteen years, in which time the conjunction and lunar aspects are nearly the same as they were nineteen years before. or Day, (solar,) the time between two successive transits of the 8un's centre over the. samf' meridian, which always begins and ends at Doon. . Day, (sidereal,) the time which elapses during tbe ro. tation of the earth Crom one star till it returns to the same star again, and consists of 28 hours, 56 minutes, , _conds. DeclifJ4tian. is the distanoe or any celestial object north or south from the equator, reckoned in degrees, minutel, &c., UPOD 8 cjrc~e which is perpendicular to it•. . l 209 A.PPENDIX. Degree, the 860th part of a circle; or the a sign. 8~tb part or Diagram, figure or representation used {or illustration. \ Digit, the 12th part of the sun's diameter, which i. or used in the calculation eclipses . . DUe of' the sun or mOOD. is its round face, which, on account of the great distance of the object, appears flat. Diumal motion of the earth, its rotation on its axis. Dorpat or Dorpt, a town of Riga, Russia, where a University alid Obse"atory were established and Ii berall y endowed in 1802. . • Eecefrlricilg, the distance between the centre of a planet's orbit, and the roous round which it revolves. Eclip88, a deprivation of the light of the SUD, by the interposition of the moon; or of the light of the mOOD, by the interposition of the earth. Ecliptic, a great cirole in the heavens through which the 8un apparently makes his annual. revol UtioD; but which is in Teality the earth's path.round the sun. It makes an angle with the equator 23 degrees, ~8 min. · utes. EltiIJorated, produced with labor, improved by succes. aiTe operations. ' Ellipticity, likeness to an oval. Elongation, the angular distance of a planet from the .UD, as it appears from the earth. It is applied only to the interior planets, Mercury and Venus. Emerrion, the reappearance of a celestial body. after having been t'clipaed. Epoch, particular period of time, period from one date to another. • Equation of time, the difference between real and apparent time, or between that shown by a true clock and a sun.dial. It depends on the obliquity of the ecliptic, combined with the unequal motion of'the earth in its orbit. Equator, or a great circle of the earth whioh separate. the northern from the lOuthern hemisphere.' When re· ferred to the heavens, ,it is oalled the Equinoctial. Equinoctial, or Celestial Equator, the imaginary circle or . IS- 210 ~B!fDIX. in tbe heaTens described by the sun in its daily revolution at the time of the equinoxes,~r its apparent passage over the line, when days and Dlghts are equal allover the earth; the centre of the ecliptic. Equi~J two opposite points in Aries and Libra. where the ecliptio outs the equinoctial. W.hen the aUD is in theae points, the days and nights are equal to each other. E"olutiora, unfolding or unrolling of any thing Ederior plane"" those which move at a rurther distance from the 8un than the earth j as Mara, Jupiter, &0. Poci of an ellipse, two points in the longest, or transTerse axis, OD each side of the centre; from each of which any two lines be drawn to meet each other in ~e ciroumference, their sum ·will be equal to the traD8verse axil. ir Gala:q, or the Milky Way, a luminous and irregular zone which encompasses the heavens, whioh is found to be composed of an immense number of stars. Geocentric place of a planet, is that position which it hlB when seen from tbe earth. Gihbmu, a term used. in rererence to the enlightened put of the mOOD, (rom the first quarter to the full, and from the full to the third quarter. GraD;", or Gravitation, that force by which all ma. . . matter tend towards each other. or Halo, a luminous circle round the body mooD. Heliacal rising or a star, is "hen or the IUD or it emerges from the sun's raya, and appears above the horizon before him ia the morning. Heliacal setting of a star, il when it is 80 hid in the lun's beams as not to be seen above the horizon after him in the evening. Heliocentric place a planet, is that in whioh it would ap~8r to a spectator plaoed in the sun. HemiqAertJ, the half of a globe or sphere. or UPBN'DIX. 211 BeUtwcii, a name given to the inhabitants of the tem. perate zones, because their shadows at noon always faU one way. Hori'ZMI, (the sensible,) a circle which separates the risible from the inYUdble hemisphere, and forms the boul'. dalY of our sigbt. H~Oft, (the rational,) a great eirc1e which is parallel to the former, and whose poles are the zenith and the nadir. Hour circk8, the same as meridians-marking the hours. 1W1merBiOft, the moment when an eclipse begins, or when a planet enters into the shadow of the body that eclipses it. 1ncli:tuJtitm, the angle which the orbit o( one planet makes with that of another, or with the plane of the ecliptic. Interior plane"', those that move at a less distance (rom the sun than the earth, which are Mercury and Venus. Irre801'Oable, incapable of being analyzed, defined, or perceived as distinct objects Latitudt of a place, its distance from tbe equator, reck. oned in degrees and minutes upon the arc o( a great circle. Latit,u,tk of a star or planet, is its distance from the ecliptic, reckoned in degrees, &c., on the arc ot a great circle. LeOflb, a star in the constellation Leo or Lion. LeIJ8er circle. of the same sphere, those whose planee da not pass througb the centre, and which divide tbe sphere into two unequal parts. Great circle. of tbe equator, meridians, &e., divide the sphere into two equal parts. Li1wation the moon, an apparent irregularity in her motion on her axis by which we sometimes see moft than the usual half of her disc. Longitr'de of a place, its distance east or west (rom the first meridian, Feckoned in degrees, &c., upon the equator. or 212 APPBXDIX. Longitude or a star or planet, its distance rrom the first point or Aries, reckoDed in degrees, &c., upon the ecliptic. ~, a body giving light, a celestial body. lM1I4I', rela~ to the moon. LUIItJtion, the time between one new moon and another; which is, on an aTenge, 29 days, 12 bours, 44 minutes, a leCOoda. ~ dark spots which appear on the face of the Bun; and Pacrik are bright spots sometimes seen on the 101ar disc. Ma,e!J,a,nic clotuU, certain whitish appearances in the heavens, in the southern hemisphere, supposed to consist either or an immense number of stars or nebulm. MtJBfIitude&. The stars are divided into six classes; the brightest are called stars of the first magnitude; the next in b~htne88, the second magnitude, &c. Mea motion of a planet, that which would take place ir it moved in a perfect circle, and equally every day. Meridian, a great circle of the sphere which passes through the zenith and the poles, and is perpendicular to the borizon. Meteor., transitory luminous bodies in the air or sky. Micrometer, an instrument fitted to a telescope to measure Tery small angles; as the diameters of the planets, &c. MicT08copic, relating to the properties of the microscope, -an instrument for magnifying small bodies by an are rangement of glasses or lenses,-to be seen only with the rmc~pe. . Milky Way, Via Lactea, or Galaxy, the broad white path or cloud, seen as 8uch by the naked eye, and vary. ing in width from 5 to 16 degrees, but found by the telescope to consist of innumerable stars, (8 or 10 millions at least, l and . assemblages of nebulm and closters stars, the mingling light of which evolve whiteness. Mythological, relating to the fabulous, though 80metimea beautiful stories and theories of tbe ancients. or Nadir, that point in the heavens directly opposite to the zenith, or imm~iately under our Ceet. , APPENDIX. 213 N,1Ju1a, luminou8 sPots in the heavens, or clusters of amall stara, discovered by the telescope. NocturMl arc, that space of the heavens which the SaD apparently describes from the time of his setting to hi. rising. NOtk8, tWO-points where the orbit of the moon, or of a planet, interseQts the plane of the ecliptic. 1Vucleu, a term used to denote the head of a com~t. Oblique tuctmBitm, an arc of the equinoctial contained between the first degree of Aries, and that point of it which rises with the centre of the 8un or atar. Oblique Ipilere, that position of the globe in which either or the poles is elevated above the horizon any number degrees less than ninety. Ob.eroatory, a place or building fitted up and provided with proper instruments for observing celestial bodies. Occultation is wh~n a star or planet is hid from our Bight by the interposition of the moon or some othel planet. Oppoaititm, an aspect of the stars or planets when they are 180 degrees distant from each other, marked thus, 8. Orbit, the oune which a planet describes in its revolu. tion round the SUD. Orrery, a machine to represent the motioDs of the plan. etary bodies, 80 named in honor of the Earl of Orrery. 08cillatory, moving backward and forward, like a pendulum. or Paralla:t, the difference or the place or any celestial object 88 seen from the surface of the earth, and (rom ita centre. Para'lloz of t1ae eartA'. amaual orbit, the angle at any planet 8ubtended by the distance between the earth and the lIun. Parallela of latitude, small circles of the sphere which are dra WD parallel to the eq nator. Penumlwa, a faint shadow observed between the perrect shadow and the full light in an eclipse. . . Perigee, that point of the solar and lunar orbit which is nearpst the earth. , • 214 UPBNDn. Perilaelior&, that point of' the orbit of a planet nearest the 8UD. Pemcii, the inhabitants of the frigid zones, named because their shadows go round them ror six months, or fall towards opposite points of the compass. Perturbation, disturbance, disorder, disquietude. Pluss, the different uppearances of the illuminated _ parts oC tile moon or planets. PkeflO'lMftOf&, any extraordinary appearance in the heavens, 8S a comet, &c. Planetarium, an astronomical machine for showing the motions and other phenomena of the planets. Planetary, relating to planets. Pleiadel, or the seven stars, aD assemblage stars in the constellation Taurus. . Polar circles, two small circles, 23l degrees from the poles; the arctic in the north, and t6e antarctic in the BOuth. Pole 814,., a star of'tbe second magnitude in the tail or the Little Bear; so called, because it is near the north pole. Prece8ritm of tile equi".el, a slow motioq the two points where the- equator intersects the ecliptic, which go backward about 50 seconds in a year. 80 or or Quadrant, the fourth part of a cirCle; or an instrument or (or measuring angles, and taking the altitudes the SUD \ and other heavenly bodies. Quadrature, that position of the moon when distant 90 degrees f'~om the sun; as in the first and third. quarters. Badia Vector, a line supposed to be drawn rrom the centre or any planet to the centre oC the sun, which, moving with the planet, 8escribes equal areas in equal times. Refraction, the bending of the rays or light in passing through the atmosphere, by which the heavenly bodies appear mOTe elevated than they really are. Refrangible, capable of being bent or tumed aside. Regula, a star of the first magnitude in the conltel1~ lion Leo. , RuoZ"dle, that 215 .l..P1»BNDIX. whic~ may be analyzed, brought. together and explail)ed or defined. Retardation, hinderance, act of delaying. R",."ade, an apparent motion of the planets in 8O~e parts of their orbits, when they seem to go backward, or contrary to "the order of the signs. Right a8cenaitm is that degree of the equator which cornel to the meridian with the sun, mOOD, or star, reck. oning Crom the first point of Aries. Rotation, the motion of any heavenly body round ita axis. " &tlllile8, secondary planets or mOODS, which revolte roWld the primary planets. " " Selenograp1ay, a repre~Dtation of the moon, with a deacription oC her different spots and appearances. s.tik, an aspect of the heavenly bodies, when they are 60 degrees distant from each other. Sidereal, of or belonging to the stars •. Sign, the twelfth part of the ecliptic, or 30 degrees. Sina, "the Dog Star," one of the brightest in the heavens, is in the eODstellation Canis Major. Solar, relating to the sun. So18titial pointB~ the first degree of Cancer and Capricom, at whioh the ecliptic touches the tropics. SpAere, the concavity of the heavens in which the atara appear. Sphericity, rotundity, roundness. Spica, a atar or the tirst magnitude in the constellation Virgo. " . Star Dul, clusters oC small stars appeariDg like sparkling land. Stellar, relating to stars. "" " Sy6letlt, a Dumber of bodies revolving round a common ~ntre, 88 the planets round the sun. .t )1" ',. ," SY:1gy, a term ~ually applied to the ~~R,.'rip~~' 'in opposition or in conjunction, or when at t~"H'Yc .9 r ,fWl. ['('If! I • ~ '\ Telucope, an optioal iDstrument eo, the,;P~f~ or,vj~~ ing distant 'obiects, particularly the IU~ W90~i' 'pl~H~m. 216 APPBKDIX. and Italll. Telescopes produce their effects e.:ther by refraotioD through glasses, or reflection from speculums. Telucopit; 8tar6, those stars which are only visible by meanl of telescopes. All stars beyond thoee of the sixth magnitude are reckoned telescopio stan. Torrid zone, that part the earth whioh is contained between the two tropics. Trajectory a term applied to the orbit a comet. TraMit of a planet denotes its pa.ing oyer another planet or star, or aoro. tbe disc of the 8un. Trine, an aspect of the planets when they are 120 de,rees distant {rom each other. Tropia, two circles parallel to the equator, and 23 degrees 28 minutes distant OD eaoh side of it. They are Ilamed Cancer on the north, and Capricorn on the muth. or or Vertical circle., the same as azimuth circles, or .ucla as are drawn perpendicular to the horizon. Prime W11ictU, is that azimuth circle which passes through the east and west points or the horizon. Year, (the solar,) the time which the IUD tak~ to p888 Crom one tropic till it returns to the same again, and is 865 da Y8, Ii hours, 48 min utes, 49 sooonds. Year, (sidereal,) the time which the sun takes to pass Crom any fixed star to the same again, and is 885 daya, 6 hours, 9 minutes, 9 seconds. Zenitl, that point or the ·heaveos immediately oyer head. Zodiac., a zone surrounflirlg the heaven., 18 degrees broad, in the middle of which is the ecliptic. . The orbits of all th~ old planets are included in this zone. Zodiacal, relating to the Zodiac, great circle of the 8phere, signs, &c. . Zodiacal light, a brightoess sometimes obae"ed in the heavens, somewhat similar to the MilJtr, W ay. Zone, a division the sphere betweed two parallels at latitude. There are fiye zonel; one torrid, two temper• .,18, and two frigid. or QUESTIONS ELEMENTARY ASTRONOMY. BY H. MATTISON. LBeSOM L-WBAT do we undel'Bland by the term .eime,1 What is utnnltnR, 'I How do the son and moon compare with each other in their apparent· ••, 'I How with the other heavenly bodies 1 What ditFerence in their liglt'l What· Mid of their change of POfttion with respect to each other1 What said of the different appeartJflee. of the mOOD 1 What remark respecting the 1&onu of the olel and Dew moon! In what directitm does the mOOD actually 1(0; and how is it 88Certained 1 What Rid at ber enering, or Ob8CUnftg, the etars 1 What of the Uric line. or Hurd upon her face 1 Wbat is an ,elip.? Hal'e you eyer seen one 1 Was it of. the "", or moOfl? What laid of the apparent me of the stars 1 What of their relative fIOfttiou1 What exceptioD8 to their general apparent fixedness 1 What in-'pltJrity is obae"ed in their motiona1 What Rid of the fIUW1&iftg and ,wai.g 8tar 1 Of the staN about the North Pole 1 Of the eluJng. of the pHition, from winter to II1IIlmer, &C. 1 May all the p~enomena thua far enumerated be obeerved by the fUJked ,ye, or without teleeoopee 1 How did the aftcimt. lItudy astronomy 1 Of what is the leieDce of utronomy compoeed, and how HI it constituted t "fl.'. a.-Where do we find the oldest recorda of utronomieal science 1 What clU8teftl of Itar8 aN there mentioned, and in what books 1 How doee the Bible J'eprel8Dt the earth 88 upheld 1 What Greek philosopher taught utronomy before Christ, and who in the second century after Christ 1 What W88 Ptolemy's theory called t Where did it locate the earth 1 De8Qribe the Ptolemaic theory in detail, and illustrate by the ma~ a.-Were there any special difticultiee in the theory of Ptolemyt What is the fir., mentioned by JOur author1 What ia the 8tcontJ1 What ill the ,Aird, anel how , it illustrated 1 What is the fOJl,rtil and last diftioulty named 1 What woold be the hourly motion of the upon thil tbeory 1 jlpw Iwiftly would it require the nearest ped .tar. to move 1 ~ucb an abBord theory ever generally believed , How long did the doctrines of Ptolemy prevail? .u. 218 aU.BN'IA.BY ASTBONOMY. ~-Who originated the preaent generally received syatem of lUItronomy? About ",bt tirM 'I What is this theory called, and why 1 How dOM thilllJ8iem aecoODt for the apparent daily motion of the .un, mOOD, &0.. tiom eut to west 1 Do we ever suppose objects to move that are at real, .amply beea. . . . are moving? Give aD illustration. Where doea the Copernican theory place the .un 1 Wha.t two motions doee it attribute to the Dumeroul worlds that 8UlIOWld him 1 What doea the first of these motiona produce, or cause? What the I8CODd? What map illustrates this theory 1 Where is the 8UD Men on the map 1 Where the p1aneta, and hed &tara1 What is meant by the orbit of a pJanet, and how repreaenteci on the map 1 In what direction do the planets move around the IUD 1 How indicated OD the map 1 What particular fact is referred to .. evidence of the truth of the Copernican theory t .,.tem a.-What are the fiIIIt grand dil'ili0D8 of the 1lDivene 1 What is meant by the 101M' 'I What by the . . . . .1 "~tft)eftl 1 How is the lormer situated in reapect to the latter 1 Which of theee, grand diYirioDa Is m.t eoMidered by your author 1 ••-From what doee the eoIarllfBlem deriTe ita ~ame? What are the bodiea of our IIJ8iem called, as a whole 1 How are the BOlar bodies 6IIt divided 1 How is the Bon distinguished from th~ planets? The planets from the BUll? What does the term planet ngfti/y ? How are the planets d;,,;ded'l What are the prifUrie., l)eecribe the eeeontltwUJ.. Point oot. each OD the map. •Which are the itaim. planeta, and wby? Which the esttrior 1 What are the ..teroilU? What are t:tmaet., and how distinguished? Poin. out the clliFerent cla.ea of IOlar bodi. on the map. pltJ.,. V.-How many fWi"'tJrY are there? What are their tatJtnd'l Wltat are they generally Damed after 1 In heathen mythology, who wu lfIercury, and what does the astronomical sign of this planet repreeent 1 Who wu Ven•• , and what is her aigo 1 What two ligos repl'e8eDt the Bartl 'I Who W81 lfIar., and what iB hial .ngn t Deecribe V uta, and her lip; A.trea, and her sign; Juno, and her 1Iign; Cer••, and her lign; Palla, ·and her sign ; Jupiter, and hie sign. What il the origin of the sign of J opiter? Deseribe Bat"'NI, and hi8 sign. FlOm what did Her.cla,' derive his name 1 What other namel haa he 1 What constitutes his siln': From whom does Verrie'1· derive hill name? Of what is his sign compoeed? What Dame did the Board of Longitude of Paris recommend for thiB planet 1 Can you make the Bips of the different planets UPOD th6 black-board? [The clua showd here abake and explain the diit8r. eat lipl, in cODII8CDtive older.] Make the trign for "~ID, Iudf-".-n, and full IIIOOfL The IIigDa of the IUB. What doea the first repre_at 1 Find the 8everal primary planeta on the map. When mouid Le VerrUr be placed 1 u ~ .. • QUBSTIONS Foa UAXllIATION. 219 What is the .cale of flu. employed OD the map? Give the diatancee of the several planets, comnlencing at the BUD. What Baid of conceiving justly of vast distances 1 At the rate of five hundl'ed mil.. per hour, how long ould it require for a body to paaI from the sun to Mercury 1 How long from the IUD to our globe 1 How long to reach HelllChel? What illustration employed 1 How long would it take for a train of ears to pass from the sun to Mercury, at thirty miles per hour 1 To our globe 1 To HellChel1 To Le Verrier? How illustrated by refere.Dce to Whitney'8 proposed railroad 1 If a train of C8l1l had left the SUD, at the creation of .the world, to visit the orbit of Hel'lChel, where would they be now 1 How much longer would it require to finish the journey 1 To reach the orbit of Le Verrier 1 8.-What is the subject of this lealOD 1 ttJ1&CU 8.-What is the subject of thia Ia.on? What i8 a circle 1 A . qUGT."t 'I A 8ezta'llt? A Big'll 'I A degree 1 A minute 1 A ~cOftrll mnstrate these several divisions of a circle, by the map. How P,iany degreeS are there in a circle 1 Have all circles the _me nuwber of de~ees1 l\tlake the 8igns for degrees, and minutes, and BeConds. What is measurement by degrees, minutes, ·and seconds, called 1 I 1O.-Giv& epmples of anpar measurement, distance8, diametel'l!l, alti.tudes, and velocities, from the map, Fig. I. How does the flutance of the observer from an object eiFect ita apparent magnitude, &c. T How ill thit illustrated by Fig. 21 ll.-Upon th~ principJee of the preceding le8lJOD, how would the 8OJ1 a.ppe~, viewed from Mercury 1 From Vena 1 From Le Ver .. 1 ~rom Sir;'IU? What is the angular diameter of the BUD, lUI vie.wedfrom our globe 1 What would it be from Mercury 1 From JUliter 1 From Her.chel? From Le VefTier 1 What idea o~ the distanc, to Le Verrier would arise from the diminutive appearance of the lun, if viewed from that point 1 ner lA.-What is the I1lbject of this )elBOD 1 By what rule do we determine the 1'8Jative amount of light received by bodies placed at unequal distances from their luminary 1 H~w is th.. rule illustrated by Fig. 41 18.-By applying the role of the preceding 18llODB to the planets, aud 8upposing the light and heat of each to be proportionate, what would be the r,'ati,,~ light and heat of Mercury, Venus, &c.? What. then, would be the average temperature· of Mercury 1 Of Veo.. ·r Of Jupiter? Of Saturn 1 Of Hel1lChel1 Of Le Verrier 1 II it certaiD_ that the light and heat are proportionate upon the several planeta 1 What said of the te1nfJerature of Mercury? What of the temperature of Jupiter, 8aturn, H ••chel, aDd IA Verrier 1 "1 120 RLS• •KTAaY ~ONO.Y. 1"-What ill the IUbject of tllia ..... 1 By what acaIe are the drawn OD the map 1 .. the IUD drawn upon the la1De acale 1 y not 1 Giye the . . . .w. of the .vera) pluets, beginning at Mercury. Do the rela&iYe" on the map 888m to etIITttepoRtl with til. . diameterw t At fotty tho.aad milee to an inch, what should be the diameter of Satam, on the map, aocordiDg to the table of magaitud. t What mould be the diameter of the earth t ~be.. JA-Of wbat doea tbille.oJl treat 1 What ill the scale o( map 41 What ia the actual diameter of tbe _D, in mil.? At forty tbousaDd miles of diameter to aD inch, how Iarp must he be drawn to correa- . poad with the other pluetl t What is the b.lk of Mercury, 88 compared with the earth t Of VeDUi t Of MBl'B 1 Of Jupiter 1 Of 8atum 1 Of HeJ'IIChel, ud Le Verrier 1 \Vhat iI the bulk of the _11, u compared with our I(lobe 1 What u compared with the whole aolar lyatem besides 1 How many global like ours would it. take, if laid lide by Bide, to reach acJI)88 the IUD'. diameter 1 What illustration of the lUIl'1 magnitude is drawn from the moon'l ntl 1•.- What i. the IUbject of thillellOn 1 What is meant by tkrt- .'y 1 Give examplee of lubatancee or diftereDt deDSities. Have all the pluetl the ..me deDlity 1 GiYe the de_ty of the levera) plan. ., 88 compared with the earth, aDd the lUb8taBcee with' which they ID08l nearly epee in weight. IV.-The aubject of thille110D 1 What iI meant by grtIfJita.titm 1 What COD8titutea the lIJeigAI of bodi.l Upon what does the amount of weight depend 1 Do luge bodiee .l••g. attract more strongly thau small ones 1 Why not 1 Do the planetl dift8r in their attractiYe force 1 What would a body weitrbiDg one pound on the eartl&, weigh upon Mercu,., 1 Upon VdU, &c. t What upon the "'" 1 Wbat .aid of the attractive force of the ..teroitU 1 Is the attraction of the planets in proportion to their bulk 1 Why not 1 18.-What iI meant by the ~dit: rnolalio" of a planet 1 What give tbe periodic times of the aeyeral plauets 1 What coastitatal a planet'. ,car 1 Do all the planel8 mOM with the MIme Nlocity 1 by ita periodic tUM 1 Cu Y011 U.-What ia the lubject of th. le.oD 2 Can you give the hour11 motion of the leVeral plane.' ".-What is meaDt by the centripet.l force of a planet 1 What by the centrifugal 1 What would be the result were the centripetal toree .uqeadetll What if the centrifugal! Why doea Mercury JeyoIye more rapidly in his orbit than any oth. planet 1 Why do the more distant planets move 10 1I0wly t What particular fact Ie- , Ql1BSTIONS POll BLUlINATION. 221 8pecting the motions of the planets is mentioned u exhibiting the ...dom of God 1 AI.-Have the planet. any revolution' except around the IUn? What .. it called in the caption of tbis le&80n 1 What natural pheDomena are produced by the revolution of the planeta upon their &%68 , Recite the time occupied in the diurnal revolutjon8 of the several planets, 80 far 88 known. What do you observe 88 rather remarkable respecting the fi1'8t four planets 1 What peculiarity in the time of Jupiter and StJturfl ? How many days have Jupiter and Saturn in ODe of our ye81'll1 How many has Jupiter in one of Ai. years 1 How many has Saturn in one of Ai. years 1 How waa it ucertained that the planets had a diurnal revolution 1 Has the motion of the planets 'on their axel any eJFect in modifying their form.? aa.-What effects would fol1ow if the planets were culM. instead of globe. 1- Are the planets exactly spherical in their forma 1 What is their true figure T Where is their diameter greatest 1 What causes this flattening or oblatenesa1 What is the di1Ference betwee. the polar and equatorial diameter of the aeveral planets 1 fIa.-Wbat is the ecliptie? Point out the ecliptic on the map. Why is the eartb represented of different siles1 What said of her pAtUe., color, &c. 1 What do the arrow. set in her orbit indicate 1 What further'ilIustration of the ecliptic is given by the author 1 Are ~e SUD and eurth always in the plane of the ecliptic 1 a..- What are the pole. of the earth 1 What the pol. of the ecliptic '-'!"- How illustrated by the pointer and map? A.;e the ecliptic and tbe eartA'. 'qtuJlor in the same plane 1 How, then, with their pole. 1 • •-How dOe. die ecli,tic lie with respect to the earll'. equ&,or? How d08l this affect the position of the .un at di1Ferent 88880_ of the year? Does the plane of the equator pass the ecliptic perpendieultJrly or obliquely? What angle is included between them? I What is this deviation of the ecliptic from the plane of the equator called 1 Can you illustrate this subject by the map? ....- What is the Zotli4c ? How ia it represe~ on the map t What portion of the heayeDa does the Zodiac include 1 av.- The .u1Jject of thil leIIOn t How is the Zodiac ditJiiletl1 Bow are these diviaiOD8 shown on tbe map? What did the ancientl imagine respecting the stuB of each sign? Wha.t are the name. of the twelve signs? Can you make their .ymboZ. on the black-board 1 What notion had the ancient utrologift. respecting the signs? Are there any that BtiU hold to thia idea? Ie it correet 1 What do theJ BLBJDNTAay ASTaONOXY • .... 10 UDClerItaDd bJ the ..ont " . . 7" What iI ita true meaai. ill AatroDomy t aa.-Its .abject 1 What doee Figure 1 on the map zepreaent? What ia the plane of the ecliptic 7 [23] How lIWly times muat a plan~t pua tbrourh the ecliptic at each revolutioD 1 What are the poiDti caUed where a planet cutl the ecliptic 1 How are the nodes &tinguilbecl1 Can you make the utronomical lip for eacb" What • meu.t by the lilae 01 tile JIDda 1 PoiDt it Ollt on the IDap In the _ure, where ia the A.:,,,tli"l1 Node placed .. respects the Wbere the tU.cmtlinK 1 Doee the fipre -repreeent the actual poeition of the node. of any planet'. orbit t .,081 "'."t . . .- What iI a 1 Which of the planets make traD8itB oyer the 81ID'. diIc gible to us '1 Why do not the other pillneta 1 What pluebl would make tnuuit. if we were placed upon Hencbel1 Where mOlt the planet making the traoait be, at such time, ia reI!p8Ct to the nodea of itl orbit 1 How with the obeerver t Wby do aot the i.uer1tw planets make traoaits at every conjunction with the IUD 1 How could this be etFected while their orbita do not coincide with the ecliptic 7 How are tranaita calculated" How often can Ibe Earth aDd Mercury meet at the same node 1 8O.-Subject " In vut fIIORtu do aU the trausits of Mercury occur 7 W!ty is thi." At which node do hi. Ntm,mb. transits occur 7 His May transita 7 Do the f.raD8its in the table conform to tbe ratio laid down in Le.on 29 1 Did you ever lee a transit 1 Wben doeI the next traoait of Mercury occur I 81.-Subject'1 Bow many revolutions ofVenas equal eight of the earth 1 Can you state of the other periods in tbe table 1 Where . . the liM 01 Vs"" ..de. lie 1 Wben does the earth p. . these peinta in the ecliptic t What fact fonoWil from the lut-name1l circumstance t When doee Venus make the next \nmsit t How mauy, yet to occur, are laid down in the table 1 Are those predicted to occur in accordance with the ratios given at the commeDcement ef the leaJOn 1 anr lSL-Subject'1 What do you undemtand by an ecliPft 7 [231 What are the orbit. of the planets t [4] What does Fig. 1 on (he map repreeent 1 • Is any planet's orbit thus inclinoci 1 What does Fig. I repreeent 1 Where is the Bun placed 1 What represents the EcLip. tit: '/ What are eeen on the ript and left 1 What do the plain linee represent. 1 Where do you find the names of the planets, IUld where the amount of their inclination respectively 1 How mucb is the orbit of Mercury inclined" That of Venua t Earth 1 (Tbink, now.) KanJ, &0. 1 Wbat part of the map represents the ZodiGc 1 Where do most of the planets' orbits lie, as respects the Zodiac 1 What ex- QUESTIONS FOR BXAMINATION. 223 ' eeptiODS" Hence eomet!mea caUed what 1 What two objects are seen near the middle of the figure" What di1Fel'8nce in their direction 1 What fact is this designed to illustrate 1 a.-Are the equinoctial and eeliptie in the .a1M pla1U? At what angle do they intercept each other 1 What is tnre.trial la'iCude? Is ctle.titll latitude reckoned from the equiftOctial or cele.tial ~quator? From what, then 1 What, then, is cele.tial ,latitude 1 What aeeming contradiction folloWi from tbiI fact" a".-What is longitude on the earth 1 From ."hat point in the heaveD8, and A.ow, is ceJestialloDgitude reckoned" What is the map, as a whole, a repl'elJ8ntatioD of" How must it be placed to answer to the Zodiac in the heavens 1 Show me where you begin to reckon longitude on the map, and where you end. U Aries, {or instance, were directly overhead, where would Libra be" What is the IoDgitude of the Twins; the Lion; the Balance; the Goat, &C. 1 aa.-Subject t In what ligu are the node. of Mercury'. orbit 1 Where and lunD ia this illustrated" Which Bide of the ecliptic is con_dered lUI aoo.,e, and which belo." 1 What, then, is it to aBcefUJ above, or de.e,ad below it 1 What do the arroVJ. near the sun show '7 What the next pair" Why ia not the longitude of both Dodes laid down in astronomical ~blee t What example does yoor allthor cite 1 Can YOIl give the longitude of the tUCending node. of the plan. JNpectively 1 aG.-Subject 1 What is a eouteUation? Do the ng.. and eonlItellatiou of the Zodiac bear the Bame namea" Do the signs" gov8I'D" different pa11I of the human body, u stated in lOme almlUllICII 'f What are tbe nelme. of the coustellatioDS of the Zodiac 1 , aV.-Subject 1 What does Fig. 1, Map 5, represent 1 When the earth is in Libra where will the 8t1D appear to be 7 As she paase. around to Scorpio, what will the BlID appear to do 1 He~lce what doee the sun seem to do ODce a yearl How is lb. illustrated by Map 61 What is the earth's longitude on the 20th of March 1 What sign does the aun ~nter on that day 1 When does the 8Ull enter the different signs" Does he really mo.,e around the ecliptic 1 What, then, gives him his apparent motion 1 Which are the Bpring signa, and why 80 called" Which the 1 The autumTUJl? The .inter ? ."""1Ier ".-Are there any Stan above UI in the daytime 1 Why do we 8e8 them" If we could lJ8e them would they be the same th~ ..e noweee in the Ilight 1 What sta1'8, then, are above us in the daytime 1 Are BtarB ever visible iD the daytime 1 When 1 How 1 Why do the stars rise earlier rwd earlier every night froID year.l.o DOt BLBKBNTABY ASTRONOMY. ,ear' How do you illOltrate thia .abject by the map 1 What other II8IB do you make of thiI map ? ".-Subject! Why are the names of tho tIIORtu placed 88 tb~ a~ OD the map 1 Do the months &Dei aigus .,.~e ift longittuk1 Which • entered fint, the new np or the Dew fIIOfItll What. the difference of time 1 HoW' is this mown on the map 1 .y.-Subject 1 By what imagiDary IiDeII is the Zodiac divided! Ilow distinguished on tbe map 1 What are the equiftDctial point. in the earth'. orbit 1 Why 10 called? What. tho equi1lOc,iGl? When doee the earth pall the equinoctial poi,:,bI t Bow are these points diitiDgoilhed 1 G..-Subject 1 I. th. an easy or a difficult I.,.,n 1 In what are the equinoctial points t What do you QIldel'8tand by the " Prece"''' 01 tle Equinoze. 1" Ia it an actual preceuion of the equinoxes, or a reee• .una 1 Do the equinoctial points, then, actual', recede 1 What i. the amount of their anDual motion 1 Are the equinoctial points fixed points, then 1 What, tben, constitute the "erul aDd autumna' equinoze. 'I What constituteI a fUlt.rlll or tTOpie," 'I II the equinox reached before the earth has made a comple&18 periodic revolution 1 How much more time is requisite to complete a nilereGl revolution t How long does it take the .un and equinoxee to fall back a whole degree? Do the ftgu recede like the equinoxes 1 Which way do they seem to move from the equinoxesl . What doee thi8 motion require in regard to mapa and celestial ff!0bes1 How often does tb. recelBion of the equiDoxes amount to 30 1 ftgnB ,ttl,· .a.-Subject 1 How are the lOl8tieitJl point. represeDted on the map 1 When does the eartb reach the _",mer 8Oletice? Wbell8 does the nn leem to be tben ? When does the earth reach the winter solstice? Where is the IUD then? What causes tbe tlecliUhDa of the SUD north and IOUth of the equinoctial? .a.-Subjeet 1 What are the Colwe. 1 How are they distingui8hed, and why? How are they compared to meridians? How do they divide the celestial sphere? How illustrated by hoopa 01 wire 1 What is gained by knowing the place of the colure. ill the heavens 1 .a.-Subject 1 Upon what supposition bas your author p~ eO thus fa~, .. respect. the planets' ~rbits 1 , What is thE-ir true figure 1 Where ill this represented 1 Are the planetary o~bil8 all &lib in this respect t What bodies have orbits still more eUiptical2 Whore is the BUD found .. respects the centre of these elongated orbits t Illustrate by the map. What. the point where the IUD is folUM! ealled 1 I' QUBSTIONI POB BUMINA.TION. 225 ".-The .abject 1 What iI the periluliora "nat in a plUle". orbit 1 What the sphelio1& 1 What do pmgee Uld spog" meaD in respect to the moon 1 Point OIIt the periJ,..lioa aDd s,helion pointe in tho earth'. orbit, on the map. What i. the dilerence between the perihelion and tJpAelUm distance of a planet 1 What i. meant by ita ".." distance 1 Whicb distance i. given in Le.on 8 1 What do you uDdentaod by the longitude of periieliGul 111 what longiwde is the ea.rtla nearest the sun 1 Can you point out upon Map 6 the perihelion pointe of the several planeta" accQI'ding to the long;' lade given in the table? . • •- What i. the lobject of this leaIOn' What is meant by the eccentricity of a planet's orbit 1 How illU8U'ated by the map 1 What iii the eccentricity of the orbit of Mercury 1 or that. of Venus1 or th. Earth 1 If the BUD is 1,618,000 mile. ODe lide of the centr, 01 the earth's orbit, M1D much nearer the aun iB tbe eartb at periAelilla thau at aphelion? Which of the planetary orbits are tbe most olliptical? Which is the neare8t a circle 1 ~.-Subject? How much is the ,srti'. as;' inclined to the ecliptic? Where is tb. illustrated 1 What other fact ia iUuatrated by the aame figure 1 When does the light of the IUD extend to both poles 1 When have we the greatest amount of .uolight in the fUWlh..n hemisphere? Is it .ummer or winter here, then 1 . Where, on the map, il the earth at tbis time 1 Where iI the eartb at the time 01 the wintn- aolstice? What bu the lun appeued to do betweeu the lummer and winter 80Istices 1 What iI thU8 prodllced by hit 888ming change of position 7 Are we neareet the Bun in nm,ner, OJ' in ."inter? Why, then, ia it Dot warmMt in thenortbem hemiapheN in Decemlwr '/ How"..., the eccentricity of the earth'. orbit atFec& ihe88880D81 ".-Subject? What do yon undendaDd by the BlUl'. ""li.tilm 1 When dON he have ttOrtAern decliQatiOD 1 When ."thena? Wbat ill his declination at the time of the eqainox.? WbeD i. it greateat? What figureI illuatrate this anbject? Wbat dON Fig. 2 abow 1 What farther iUUBtratiOD have we io Fig. 31 Point out the place of the .aD at the .time of the wiater -ut.it:& Where ia be on the 20th of March 1 Where on tbe 23d of September 1 Where on the 21st of JW1e 1 Is he directly overhead then 1 How many degrees does he lack of it, according to the figure8 7 What iI meant by the ~enitA poiat'/ From all this, wbat do we learn respecting decli1UJtio-n '/ .....-Subject? What do you underataad by right lUcen"'? Wbat is the equintlctiaZl [40] WIlerein doee c.le.titJllatitude diJFer fiom twre.triGll What oelestial meuuremeutl, theD, 8D8wer to latitude aDd longit.ude o~ thE' earth? Could you understand and remeinber tlecliutitm and rigAt MCeuitm better, if they were c.W · 226 BLBKBNTAKY ASTRONOMY. eel_a! "tu.tle and ltmgihltk'l What does your author thiak of mch a chop of tel'DW 1 How many tkgreu of right 88C8D8ion can there be 1 Wherein do rig'" fNCeuioa and cek.tilUloagitutk diWel't aG.-What iI the ,eliptit: 1 What are the orbit. of the planets T What .. the IAlbjece of I~n 32 ! What the subject of this lesson" \Vhat doee your author ..y of thiB l.,.,n 1 What represent. portiOD8 of the planetary orbiu on the map t How are their leveral tlSU Ihown? Ho.. their efl&dtor.? Their .OftU 1 Upon what does the tztent of the torrid lODe or a planet depend t How does the sun'• .ucliutio" north and BOOth of the equator, and polar iacli1UJtiou agree 1 HoW' doe. the tonid zooe compare, in iu extent, with the polar inclination of a planet 1 Do you no.. undentand Aot.O the incli. nation of the UN of the planet. "cta the extent ad character of their .on. 1 What .aid of Mercury, the 8IIte1'oid8, Henchel, and La Verrier 1 , Il.-Upon ..hat two C&UIM do the 8881OD8 of the planets depend 1 What doee the former determine" The latter 1 Illustrate by the map. Have you reviewed I~D 461 [See quMtiOD&] Do you still remember what is meant by the obliquity of the eeliptic 1 What do YOIl undentand by tkclinatioa? What .. the clliFerence between the ,cliptic and the e,Minoel",'? ' 6fL-Subject t How far are Venu' tropics from her equator 1 Hu she a frigid zone' What aid of the 8UD'. dPClinatiOD upon Venus? Of her Ie8IODl1 CaD such IeUODl produce vegetation 1 ".-Subject t What laid of the polar inclination of Mars 1 .Are bis 8888008, then, like oUNl Why Dot 1 How many &ea8ODS has he 1 Wbat is their leDgth t a4.-Subject 1 What iI the inclination of Jupiter's axis to the plane of his orbit 1 How does thia affect hil zones 1 What said of tbe lun', declination upon Jupiter 1 Of bia temperate zones 1 His day. and nights 1 Hia poles 1 What is hia light and heat, lUI compared with our globe 1 Hia diameter 1 Ilia r,latiN magnitude 1 Hia figure 1 The time of hiI rotation upon hil aD 1 Hie mean distaooe from the lUIll A.-Subjectl . What ..id of hi. polar inclination 1 What is hiB IJeriodic time' What iI the ftUtllb6r and kng'. of his ee880DS 1 What laid of his polar regio081 Where do the ring. of Saturn lie 1 What is tlle time of their revolutioD 1 How crc.ed by the lUll 1 How are the aides of the rings alternately enlightened 1 What said of the 1888008 on the sides of tbe ringsl When will they be turD.ed edgewiae towards the earth 1 How will he be enlightened then 1 Where, ia hia orbit, will he then be 1 Where in seven and a half y8&1'1 after t 227 QUBSTIONS rOB B%AXINATION. How will hia ri~p then appear 1 What win the sun's decliDatioD t.hen be from the planet'. equinoctial? What will follow in seven and a half y8&1'8 more 1 When wW hiB riDga become iuvi8ible? Why can they not then be Been 1 When will they become visible again 1 Save we any Curtber illuatration of the 8881008 of Saturn, the structure of hiB rings, &c. 7 Have all the planets, then, their da.yand aight, cold and heat, winter and BUmmer, &C.1 aG.-8ubject 1 What iI celestial longitude 1 [34] When are planconjunction? How illustrated by the map 1 WhAt planets have two conjunctions 1 What are they called 1 What is the dift"erence" Illustrate by m!,p. What diiFerence in the diBtance of Venus from the esrtA at her two conjunctioDs 1 How explained by the map 1 What conjunction has the e:cterior planetal Why Dot an inferior conjunction 1 When is a planet said to be in oppo•• tion 1 What .said of the rising and setting of planets in COllj unction aod opposition 1 Make the astronomical signs for conjunction and opposition upon the black-board. As VeuUI, passing eastward, fonDS a conjunction with the sun, how does she usually p888 him 1 How ia this accounted for 1 When does Venus pU8 over the 8un'e dISC 1 How is euch transit illustrated by the map 1 ets said to be in av .-Subject 1 What ia a nderesl revolution of a planet 1 What .. synodic 1 What is the dift"erence 1 How illustrated by the map 1 How long from one inferior conjunction of VeDus to another 1 Why do the synodic periods of Jupiter, Satlll1l, &c., vary 80 little from the periodic time of the earth 1 , SO.-Subject 1 What di1Ference between the diTect and retrogratk motioDS of planets 1 Can you explain the cause of this seeming retrogressioD, and illustrate by the map 1 81.-Can you explain the retrogreeaion of the exterior planeta by the map 1 What ia meant by the " (lTe of retrogradstion 1" Why have the more distant plane.. the smallest arc? retmgrading 80 short a distaDee 1 . Why 80 long in • a.-Subject ? When ia VenUl etUt, and when tl1en of the aun 1 When is abe morning .taT, and why 1 When e"",ing .tar, 8UJ why 1 What did the ancients think of this star, and how named l How long is VentJ8 alternately ~orning and evening start What I:~ meant by her greste8t e/,ongstion eut and west 1 CaD you .lluHtrb.1.0 the diWerent points in th. leIIOD. by the map 1 88.-Subject 1 What is meant by III pAtUe.1" Why do Mercury and Venus preaent different pbues 1 IUl18trate by map. When dO&t Ven.. appear largest, and why 1 228 BLBKBKTAllI' .&sTKOlfOIlY. "'-Subjeet 1 What three factB dOM your aathOl' state reapec&iIIg tbe primary plane." Baye aoy IpObI eyer been seen UpoD Mercury? By whom? What el8e does be _y he 8BW aod IDe8&lINd 1 What is the teI.copic·t»lor of Mereury" Have you carefally noticed the ten flew. of Ven.. Ihowa on the map 1 What do you auppoae theee IpObI to be'l What said of the tIIOUnt.ifUI of VeDU81 What of ber .,..,lne 1 What of her eolor 'I What doN Fag. 13 on the map repl'Nent'l Where is the obeerver supposed tD be, and how ••isted in hia vilioa1 Wby would the land appear bripteet? From what woald th. ohlerver iDfer that our globe revolved OIl her Oill, and the hnw of her rotation'l From what the inclinatioD 0{ her I1xis" From what mer that abe had an ."".,iere'l W baa Rid of lODes, colon, &c. " Whicti figures on the map are repreeeatatiooa of Mars? Have Y01l noticed the 88veral figures from 14 to 23, the views were had, and IDleR? How .. this variety or appearance accounted for? What said of tbe bright spot, Fig. 221 What Aid of the -.r/cee of MU81 What Dr. HeISChel of tbiI planet t Who coostructed a ma, of Man What is his color 1 \VIaat ia supposed to be the cauae of this roddy appearance" Can it be discerned by the aaked eye" What said of our knowledge of the asteroids? Of tbe appelU"lUlC8 of Pallas" Are the asteroids visi· b1e to the naked eye 1 What i. their t.eleacopic color ? What does Fir. 24 repreaent 1 What is his color 1 Where are his 1HZ,. 1 What are they suppoBed to be 1 What is their nUfJlb,r 1 What said of changes in their forms 1 Of spots in them 1 Is the figure an exact cBcle" Why not 1 .,.,Juma -r ".-Subject 1 What does Fig. 25 represent 1 What said of 8aturn's beltll ? IDs ringll ? Of the color of the planet and rings '1 How was Saturn regarded before the invention of the tt'lescope 1 Have you carefu1ly obBerved the diJFerent views at the top of the map from 1 to 12, and noticed what is said or them in the letIM>n'1 When, and by whom was the first view had '1 Through how long a period do these views extend '1 Where have we a correct representation of Saturn '1 What said of tbe different appearances of Saturn 1 Can you e~plain the caw, of theee di1Ferent aspects of Saturn, aDd illustrate by the map 1 For what other purpoeee may this diagram be U8ed'1 What is the fir.t fact shown '1 Dlustrate. What is the .t:fJlItl point illUltrated 1 How MOwn by map 1 What next doN it ..bow 1 Where are Satom'. .l.ti'ial points 1 His eq.inoctit.&ll How may this diagram illustrate tl,cliftGtitnN 'I Why can we DOl lee Saturn in the night at all se880M of the year? . .e.-SUbject 1 What iI Satom'. diameter? The distance tiom the body of the planet to the interior riDg'1 What is the width of this ring '1 What space between the two rings? What is the width of the exterior ring '1 The distance acl'088 the enerior ring 1 What. &he thickne'll of the riDP 1 What doea Fig. 4 reprel8nt 1 What &aid QUBSTIOIfS POR BlllIINATION. 229 of the stan" What doee Fig. 5 represent'l Describe ita diWerent part& What does ~ig. 6 represent" What additional particulars are etated by your author respecting the rotation of Sa~urD, the nature or hie rings, their actual .paralion, U8e8, &co " What said of spot8 UPOIl Herschel" What said of hi8 (ltm0llf'her~ 1 How doee he appear through a telescope 1 What. his color? What said of Le Verrier" WhaL does Mr. La.-el say of Le Verrier'. baving ring. an~ a lI(Jt~l· lit~ 1 «I.-What is the subject of this lesson'l Who discovered Mercury, Venus, Mara, Jupiter, and Saturn 1 Can you tell tDh~n aud by tDhom the other planets were discovered 1 Who demonstrated the existence of the last Dew planet 1 What otber astronomer was making .,ilniJar calculations at the ..me time 1 Who first .atD Le Verrie~ and where 1 Can you explain what has been called " Bode'll LinlJ, ' respecting the diataucee of the planl)t t How does the distal)ce of Le Verrier compare with the distanoes or the fixed etara1 What part of your book are you DOW in -I What part of the solar eystem have you DOW. gonl) over or considered t A.-What .. the .ubject of thUI clGptw 1 What of tbis le.8Oft '/ What are the eectmdaf"J planet. '/ What Dumber is knl)WD to exist " How are they distributed to the .veral planets 1 Point them out on the map. In what respect8 do the lI8Condary planets resemble the primaries 1 What porpoae do they Be8m to answer in the economy of nature 1 What are they usually caned 1 •••-Subject'l II it probable that Venus bas a satellite 1 What .. its Buppoeed pniotl, tliBttJftCe, and magnitude? VO.-Subject 7 Why is our moon an object of great interest to 1181 What i. her mean distance from the earth's centle 1 How long • she in makin, a aclereal refHJlution 7 A -ynodic revolution 1 What is her hourly motion in her orbit 1 Her mean angular motion per day 1 Her tlitJraeteT'/ Her angular diameter! Her bulk aa compared with the em' 'I AJJ compared with the BUn 'I What is the iacliDation of her orbit to the ~cliptit: 'I The iIIc1ination. of b6r (I~. to the plane of her orbit? In what time deee she rotate upon her axis 1 How much light does she reflect, u compared with the SUD 1 Why doee abe appear u large 88 the sun 1 How does her diataDCN compare with bia 1 Do you remember in what ratio dvta'f&ce diminishes the apparent lise of bodiee 1 W /&ere and /WW is thil i"IUltuoated 1 VL-Subject? What doee the apper 'row of figul'8l represent 1 Can you explain the clI. .e of theBe various appearances of the mOOD, as seeD from the earth 1 How would she appear to a penon stationed in the 8un 1 Explain the different figuroa fl'om A to H. What ~ . ~30 ELBMBNTARY ASTROKOXY. .,.,giu, .......,...., are 8Uch a JeVoiatioD aDd the eoD8! queDt chaac- caDed., Wbf'J"8 are the &ad in the mOOD'. arbit 1 tIC"'" Va.-Wbat doea rll. i OIl the map I8p1'M8nt 1 Where are the moo.. leeR t Where are the jvll mooDS t Which in clJnjunetion, aDd which in OfIlIHititntl [56] How much of the moou is al. WI1YS eoligbteDed t ~How maay revolutioD8 does the moon make ill a year 1 What iI a laur yeu t How much shorter is it than the civil yearl .U1 What are the ,.u. of a planet'. orbit 1 Are the moon'. DOd. permanent in the ecliptic t What motion have they 1 To what doe. it amount every IQBar year 1 How long, then, does it require for bel' nodee to revolve quite around the ecliptic t Vl.--8abject t V"- What iI the .dUFereace between a ade,-etJl and .,.tlil: revolution of a plaet 1 CaD yoo illUlltrate by any figure on the mapt th. VI.--8ubject 1 What fact respecting the moon is obvious to the naked eye 1 What fonr conclusions follow from fact 1 How is it .hown by the map that if the mOOD always presents the aame side to the earth, me mU8l revolve on ber uia every 291 days? VfS.-8ubject t What iI meant by the moon'slibratiou '! What iI her libratioD in long-it'"" 1 What causes this rolling motion? What is libration in lGtitu.tk, and how is it accounted for 1 . VV.-Subject 1 What ia the leDgth of the moon'. year? What laid of ber daya and nights 1 Of the aun'. declination upon her? Of her 188801181 Va.-Subject 1 What does Fig. 4 repl'8l8Dt 1 What is meaDt by the " circle 01 illumination 1" What is the termifttJtor? How does tIlilline travell8 the moon'. diIc t What are Figs. 5 and 6 1 V8.-Subject 1 What particular fact becomes obvious by obIerviDg the mOOD with a teleacope 1 What three circulDBtancea show the eXistence of 11lJl&r motlDtaiD81 Can you ill_trate by figures 4 and 6 " What is the character of the lunar mount&iDs? Wbat did Dr. Hencbel 88e 1 What ia said of eeeing cities, fortificatious, &c., iu the mOOD °l Hu the mOOD an atmosphere 1 How d08ll sbe bppear through the moBSter teleacope of Lord Roese 1 . SO.-Subject 1 What ill the average height of the nine ptiueipcd mouDtains of the moon t Have you looked up TycJw, Kepler, 'Cll&c. 1 Can you point out the principal 8e. upon ber 8W'- ,ern",", face' . QUESTIONS FOR EUMIKATION. 231 81.-SubjJct? How many mOOD8 hu Jupiter' ? What are their diameter. respectively 1 What their dutancell from Jupiter 1 What thE'ir periodic tirM. 1 What resemblance i. discovered between Jupiter'. first mOOD and 0Ul'81 What striking contrast 7 How does its velocity compare with that of our moon 1 How ie tbis rapid motion accounted for 1 How do the orbits of Jupiter's moons lie 1 What iti their inclination, respectively, to the plane of his equator 1 'Vhat is said of their eccentricities 1 In what direction do they revolve 1 What said in respect to the visibility of these satellites 1 What of Jupiter and hil attendants as a whole 1 Can any member of the class point out each moon upon the map, and (ive their distancea, . magnitudes, ~nd periodic times 1 8D.-Subject 1 How many moons has Saturn 1 How is this 88eertwned 1 In what direction do they revolve 1 What Baid of the jOrm and po8ition of the orbits of the first six 1 What of the seventh 1 Can yon give tbeir dutanceB, respectively, from the body of Saturn 1 CaD any of-them be within the rings of the planet 1 [Compare with distance LeMOn 66.] What are their periodic times 1 What said of their relative magnitudes 1 How are the two interior moona ~en when the rings of Saturn are twned edgewise 1 aa.-Subject 1 How many mooDS has Hel'lChel1 Can you recite their reepective diBtanc81 from their primary 1 What ale their periodic times 1 What two remarkable peculiaritiel distinguish the moons of HeI'BCbel1 How ill the latteriDdicated on the map'l WhtLt is the general form of the orbits of these satellites 1 .,,-SubjeCt 1 Is it probable that Le Verrier hu one or more satellit.e81 Have any ever been leen, and if 80, by whom 1 What other circumstances seem to render the existence of IUch mooDS prob8bl~ 1 Do the secondaries rotate upon their respective axee? Hlive 'hey any attendants revolving aroond tlem '/ · 85.-What .. the lubject of this clapter '/ What part of the solar SY8t~m have you now considered t What is the subject of this lellIlUn? What iI an eclip., 1 A IOlar eclipse 1 A lufUlf'? \Vhore do we begin in explaining the philOllOphyof eclipaes1 Wbat is a .hadolD '/ Upon what do the length and form of shadows depend? Illustrate by map. What would be the form of the earth'8 shadow if she were larger than the IUD 1 WheD the opaque body is 8f1&aller than the luminous, how does ita ii.tance affect the I~ngth of ita shadow? Illustrate by map. What difference betwoen the umbra and penumbra '/ What, then, is the cau., of a 8Olaf' eclipse 1 illustrate by map. Which limb of the IUD .. first obscured, and why" Illustrate. What causes lunar 'eclipaesl Explliin, by map. why the ~a8tern limb of the moon ia first obscured. Why a,n, Bolar eclipeee aJ~ayl at fielD '11WO'n 1 Why luftGr at full .won 1 232 BLEXENTAKY ASTRONOMY. ".-Subject 1 What is the fil'IIt thing to be determined in calculating a eol. eclipee 7 How does the place of the earth in her oraL affect tbe length of her Ihadow? Illustrate. Why are tbe shadows of the earth and moon longer at U t and shorter at T 1 Bow does the MOOn'. position, in her orbit, aiFect Ian- shadow t What is the lAird circumltance mentioned u affecting the length of the moon'. shadow 1 When the earth • at U. and the moon in pwigee, how far will her Ihadow extend 1 What will be it. diameter at the earth'. 8urface T What of the pe""..Jwa 1 When will the eclipee be pcrtitll, and when tutal? How iI it wheD the lun and mOOD are both Dearest the BUD, a~ at T and U t How when the IUD and moon are at their "'eGR dlstancee 1 Why do the IUD and mooD appear to vary in size 1 How mWlt the IUD and mooD be situated, u to distance. for a central BOJar eclip86 to be tottJl? How 10111 may a total eclipse of the BUD last 1 When doee the moon appear ",..'l~r than the IUD 1 Should a ceotral eclipse of the IUD occur then, what would be ita character 'I How loag may the ring lut in an aDD»lar eclipse 1 What is meant by " digit. 1" Do you now tlDdentand the cauae of partial, total, . central, aod aIlR"",," eclipse81 What laid of the eclipses of 185tl, 1861, &0.1 Of thoee of 1854, and 18751 Knowing the time of ODe eclipee, how CUl we the time of oth8ll. either put or to come 1 ina or • •-Subject 1 What is the ave~ length the earth's shadow T How doee tbi8 compare with the f'I&OOft. dutaflce 1 What its average breaatl at the distance of the moon t What three circumstances are mentioned u afFecting the ezten' and duration of lunar eclipses f Illustrate the lut-named principle. Why is a lunar eclipse ever partial? Why are they fUNr G""ul. ? DelCribe the progr•• of a lunar eclipae. 88.-Wby do we not have two central eclipses ev~ry month 1 DI.... trate. Where must the mOOD be for an eclipse to occur 1 Explain by }~ir. 2. M118t the mOOD be exactly on the line of her nodes f What are the 80lar and lunar ecliptic limit. 1 To what do they amount respectively 1 Bow illustrated by Fig. 2? What singular motion have the moon'. nodes? Dluatrate. Why are we sure of an eclipse every one hundred and 88venty-three days 1 What are the flDd~ montlas ? What the leut, and what the greatest number at eclipaee per year? What the U8Ual number? 8§.-Subject 1 What caosea the occult.tUm of a .tar 1 What conc) DOns are drawn from these eelipeee of the 8tarB 1 8O.-Subject t . Do all planets cut ahadoWII? \\l1y canbGt the primarie8 eclipee each other? What said of tbe character of Jupiter's Ihadow t Of its positiOD? or the plaDe of his equator' Of the orbits of three of his mooDl t What said of the fourth, or mORt distant I&f.ellite' What is generally the cue as to Jup:ter'. moons? Abcnd QUESTIONS FOR BUXINATIOK. 233 how mallY eclipeea haa Jupiter in a month T Are they u8ually p"". bal, or tota, and why 1 What ..id of the lbadOWB of hi• •tellites1 What are the immer.um. and man.,.. of his mooD81 How are these eclipses made IMViceable in navigation 1 • 81.-Subject 1 Bu Satum any eclipeea T Why confined to the time ..hen bis riDp are 88eD edgewi8e 1 What Rid of Hel8Chol'. mooDS? 8A.-Wbat .. the IDbject of this eluJptw? Which diviBion of the book are you DOW in 1 What are the 8ubjeobl of the chapten already gone over 1 .What is the subject of this fim lealOD on tides T What are tide.? Flood tide? Bbb tide 1 How many each day 1 What ca"•• tbe tides T What does Fig. 1 repl'8IIent 1 What does Fig. 2 DIU8tr,te 7 Fig. 3 7 H()w do you account for high tides on the side of the earth oppoftte the moon 1 IllUlltrate by mRp. What is dIe 8Uppoeed amount of the earth'. perturbation, 88 affected by the moon t 83.-8ubject T Whekre ia the vertex of the tide-wave generally found 1 How illustrated by mapT What is the cau. of thialagging, or delay 1 Wby is high-water later and later every day T Why is everyaltemate tide higher than the iDtennediate ones, when the DlOOIl iI far from the eqllinootiart Illutrate by the map. ....-Subject" Ie the moon the only caU8e of tid.? What_ the cotnparative bulk of the BUD and mOOD 1 Why, tben, is not the 8UD the priDcipal cause of tides 1 What ia his inftlleJlCe upon tbe earth, in the production of tidee, u compared with that of the moon? Would the BUD .loru produce a perceptible tide-wavo 7 When both iDduencee are united, what is the comparative iaer,... of the tidewave 1 WbeD they ctnlntertJDt each other what is the reeult 1 What are theee very singular tides called? What the low tides 1 When do the .,-i'flg tide. occur 1 When the fl,ap ,ide.? . How illustrated by the map 1 When the 81lD and mOOD are' in oppofttion, bow are spring tid. produced 1 Doea your author leem latiafted with the usual explanation of tbis point 1 What objection doee he name 1 What said of ProfealOr Olmsted'. explanation 1 What does Fig. }' represent 1 What A and C T What Band F T Can Y011 etat8 ProfeaiOr Davies' theory, &Dei WlI8trate by the map T What ..ys your author of thi8 theory 1 M.-How are our tid. 1dFected by the ."'ance of the mooD? Illustrate. What principle. iUustrated at E 1 Wi.t .",.itJtion. in the height of the tidee in different parte of the world, and IunIJ eGa.ll? Wililt said of Zoea Ct.lu• • detaiDing or butenillg the tides? Of lak. and inland 118881 Of t.ltmDBplwit: tides 1 Of tides on the aft ? tNI.-Sobject 1 Define the G";de. of the mOOD'. orbit, and W. . ill mea. by the II _ _a . , ,/w .,.ular" IUIIIIraIe.. Ia what ti... iI ea e.tire nmJIaIiaa eompIeted '! 11M tbiI ...... ea, eaa..-. willa trat.. by.... ~at _,-.1 "'.-What .. the _bject 01 tbia ella,..., What aN the aubjeeta of the chapte.. preeedinr t What .. the 811bject of lb. luatna., What ..w of the C_lJeter of comeI8 t FrGID what .. their .... derived 7 Of what "..u do cc.ne........., COT • r 1 De.cn"be each. Have aU cometa a alleleu1 Bave they all tail.., What _yw C...Di of the comet 0( 16821 What. the pDeIaIllireea.. of the tails of eometa" DIWltrate. What peculiarity in the comet of 1823, and hoW' iU __ lrated by map? Row are the tail of cometa ...."y clUTed 1 What • the c:tI.. of th. clllftblre" Coakl a comet get through oar atlDOIIpbere ., u 10 .trike the earth? What aid 01 the comet of 1744 t How "'OWll OD the map 1 What.aid of the eltnt,..tio. and eotdnIe,in of the tail. of comet. t or •• expe-iOllS? or the pA,neal of comet. 1 What ",...1. of their ligbta. . 110m attnctioD 1 Wbat W88 Sir l.laac Newton's opinion of their de_ty? Bow are their .,.6iu 80IJletimM a8Bcted by the attnctioo of the plane.. ! Are .t.r, tl_ they .,If·lumillOU8, CJI' opaque bodie.1 What proof1 reality U pr, bodies 1" Are the, iD 88.-aobject81 What aid of the comparative ••e of the teaeki of comets 1 CaD yoo give the diameter of any 1 What said of the magllitude of the tait. of cometll1 Of that or 371 yeam before Chriat 1 Of A. D. 16181 Of 1680 1 Can you point out theee comMa on the map 1 Give the length or the taiIa of lOme of the moat remarkable cometL Doe. the angular length or comets, as I88D from tbe earth, Ibow their true relative length 1 What said of the _locity of comet81 What ioequalitiee 1 When ia thei!' yelocitv 6'"sate.t 1 When le.., '! W bat . u tbe anplar velocity of COIDet 01 14721 [&8 leMOn 10, and map.] What wu the ADurl, 'Delocityof the comet of 1680 1 What laid of the ,naper.'ure of comets wbeD neaJ'Mt the 8un 7 What wu the perihelion diataDCE' of tbat of 16801 What its relative light 1 Ita "eall What IAlPpoaitiOD respeCtiD, the prodsctitHa of the tails of come. 1 the ".-Subjecbl? What. the p~du: titJU of Bncke'. comet 1 Of Bie14'.l Of Balky'.? Of tbe comet of 1680 T When next to return 1 Ha ve any lltill longer periods 1 Do all comet. I'8tum to our ayltem 1 Wby not 1 What ill ProfeMOr Nichol'. opinion 1 Who COBcun witb him 1 What said or the GvtllftCe to which BOrne that retUfn must go 7 What does this prove in rerud to the distance to tbe rixed atars 7 What aid of the periA.elion avtGnce of comets 1 How were tbe perihelion points of the ODe hundred and thirtY-lElven comet. mentioned distributed? Wbat said of the ftumb,.,. of comets 7 What circumltal)c~. render it probable that their Dumber amounts to millioua7 What wu Prof~r Arago'. coBcluaion, and from what premia. 7 QUBSTIONS FOR BX• •INATION. 235 lOG.-What said of the direction of comets? What _Y8 ProfetBOr Kendall of their inclination.. 1 How is this circomstance re·' garded by him 1 What is the usual form of the comets' orbits 1 Why Dot eeen 10llKer from the earth 1 How were comets formerly regarded 1 Are. they dangwoa in the solar system? Is a collision with the earth probable 1 What are the chance, for 8uch a catastrophe 1 What would be the result, if they should strike our globe 1 What i8 Profeaaor Olmsted'. opinion 1 101.-0f what does this chapter treat 1 What is the subject of this particular le'Mm 1 What said of the po,ition, office, and coml(lf"ative importance of the 80n 1 What is his dia~ter? How llloatrated by tunnel, and railtDtJy 1 How does hi8 diameter compare with that of the earth 1 How hi. 1 How with the whole solar tyatem be8idee? How is the suhject of his magnitude iJlostrated by reference to the moon's orbit 1 What is tho true form or figure of the .un 1 Illustrate his relative diameter by the map. ma., , 10Sl.-Sobject' What does the telescope reveal opon the sun'. disc 1 What aa.id of their number 1 Are spots always visible 1 What is the greatest nomber ever visible 1 What aay. your author of hw own observations 1 lOa.-Subject 1 What is the appearance of the solar spots t Point out a ftucleu" and its penumbra, on the map. Can you name some of the principal phenomena of the solar spots 7 What did Proffl88Or Henry ascertain 1 What was Lalande's opillion 1 What thooght Dr. Hel'llChel of this soggestion 1 What W88 Herachel'. opinion 1 What said of tides on the SUD 1 To what conclusion did Profe880r Wilson arrive 1 lCK.-Subject 1 What view of the 80n is shown on the map 1 W"at 8aid of Dr. Hel8Che)'s ,observations and statements 1 or Dr. Dick's views1 What does he infer from the fact that spots have been seen by the naked eye 1 What says yoor author of this conclll8ioD 1 loa.-Sobject 1 What is the inclination of the sun's axis to the ecliptic 1 What proof have we of his revolution on his axis? Iu what direction does he revolve 1 In what tifM? What ddFeren~e hetween his tidereal aDd .ynotlic revolotioua1 How do yoo account for this difference of time ? lANI.-Subject 1 In what direction do the solar .pots CI'Oll8 the .un". d~1 How, then, can he revolve from west to east 1 How illustrated by two 8pher~1 What said of the appareut inequality of motion of the solar spots 1. How explained, or accounted for 1 liow' ~U8trated by Fig. 11 Explain their change of figu.re by the m<.Lp. 286 BLEMENT.RY ASTRONOMY. What chaDges in the apparent dir~ction of the spots at difFerent 8eUOD8, and how explained' and illustrated by the map 1 IOF.-Subject 1 II this subject well understood 1 How does the IUn appear through a teleeeope 1 What was La Place's opinion con. cerning it 1 What is the most probable opinion 1 What says Dr Herachel of the tmapw"ture of the sun 1 What calculation in reference to tbe light and heat of the sun'. 8Urface 1 What remark in regard to ignited solids '1 What does Dr. HeJ'BCbel infer from this., DOes hia conclusion ftece ••arily follow 1 What says he of a rejlecti'De caRtJpy, &C. 1 What does he consider the great mystery in regard to the- lun 1 Does chemical ltCience throw any light upon this question T What d068 Dr. Hel'llChel conjecture 1 loe.-Subject'1 What is meant by the soditJcal light? What is ita fM'fll? How does it Beem to surround the 8un 1 With what does ita shape 166m to ,correspond? How, then, do we account for its apparent 8hape as seen from the earth 1 What said of the Rature of this 80bstance 1 What is Profe&l!JOr Nichol's opinion 1 What says Dr. Herschel? What say Dr. Dick and La ,Place upon t.his point 1 Wbat are the tlimennOft. of this phenomenon, 88 given by Dr. HerIChel? What other opiuion is advanced respecting the zodiacal light 1 What -y" ProfeB»r Olmsted 1 Wbo concur with him ill this opinion? Which are the best months for observing this phenomenon 1 What interesting fact is stated by Profel8Or Nichol? What does this ...eem to indicate 1 IOD.-Subject" What astonishing fact bas been ascertained respecting the lun' How many motions haa he 7 What is the fir.t ? The .econtll The tlaird? Who aacertained the direr-tiD" and "elocity of the 8Dn 1 What i. the point of tendency? What is the estimated "elocity of the BUn? With this tact in view, how Mould the sun be regardE'd? What still more magnificent idea 1 What further ligbt is thrown upon this intereSting subject 1 Who haa the credit of discovering the "emtral sun 1" Where does he locat.. the centre of our cluster of 8uns1 What star does he fix upon as the central orb 1 What is the 8Upposed distance of Alcyone, as compared with that of our sun" }Jow does this distance compare with t4at of Le Verrier 1 How long would light be in travendng this distance" What is Mldler's estimate of the periodic tirM of the Bun 1 Of hj. ",loeity ? How does the plane of the aun's orbit lie, with ret'pect to the ecliptic 1 Where the tUCeatling notk of bis orbit 1 ,110.-What i. the subject of this cluJpter? Of tbis particular le880D 7 Can you deecribe what is cal16d the nebular theory? Wbo originated this theory? What circumstances seem tG f ••or it " I. it open to allY BeriODS objections" What ill the fir.t? What is the .eetmtl objection T The tlard? The fourtA ? The fifth? Do an1 QUBSTJOlfS FO& BUXm.TION. 287 reran! this theory incoJUJiateDt with the MONic account of oreatioa t What is the opinion of your author 1 111.-Subject? How many priDcipallaw8 that govern pJauetary motions 1 What called, and wby? What is thejir8t of these laws 1 What is an ellip,e 1 What is meant by the f1UJjor, or tranlmer.e azu of an ellipse 1 What are the foci 1 What i8 the radiu.8·."ector 1 [See map 7, Fig. 1.] What is the ,econtllaw of Kepler? CaD Y011 illustrate this law by the map 1 What i8 the tAird law 1 CaD YOIl illustrate by an example 1 Does thia law prevail throughout the solar Iystem? llA.-Subject 1 In thi8 iIIustratiou, what i8 tile relatJve diameter given to the SUD? Mercury 1 VeDU81 Earth 1 Mars? The Asteroids 1 Jupiter? Saturn 1 Herschel? Can you give any of the d"ttlRCe, accoq to thia repl'e88Dtation 1 113.-What MI,- ill the qoestion discu.ed in thw lesso11 1 What picio1& was entertained before the discovery of the asteroids? UpoD wbat was it bued 1 What influence had this opinion upon astronomen? What opinion hu been advanced in respect to the origin of the asteroids 1 What aix facta are 8Upposed to favor this hypotbeaia1 To whom does this theory belong 1 What other astronomers favor, it 'I What say. Dr. Henchel of it 1 What remark by Dr. Dick 1 What Dew theory by General Root 1 What doea your author think of Dr. Olber'. theoryt and why 1 U"-What question ill discosaed in this chapter 1 Have we any direct testimony upon thi8 subject 1 Upon what, then, is the argument based 1 What is requisite to a foil appreciation of this argument from analogy 1 What facta, then, seem to require that the planets should be inhabited 1 The first ? ' Second 1 Third 1 Fourth 1 Fifth 1 Sixth? Seventh 1 Eighth 1 Ninth 1 What argument from the animal inbabit8dneas of aU parts of our globe 1 What part of the universe, and of your book, have you now gone over? What yet .remaiDS to be coDBiderecl1 What.. meant by the BOlar 8y,tem 1 What by the .tkrealleaNU 1 UI.-What is the subject of Part II.? Of this first cAa.pttr? or this particular IMIOn 1 'Vbat four characteristics are mentioned as distinglliabing the fixed atarB 1 118.-What i8 the ftrIt step in cl8llifying the stars 1 What the .eoad1 How many magnitudee1 Whioh are visible to the llakt'ld eye, and which telescopic 1 Illustrate by map. Does this cJaaI.fi· cation indicate their tlctutJl relative magnitudes? Why not 'l What is the third step in clusifying the stars 1 How are the individual IWB in each coD8tenation desipated 1 What is the fourth help in 238 KLEMBNTA.D. Y A.STRONOMY. finding and Dumbering atan1 The )ifth1 Can you give lb. "allie' of any stara T Can you Dame any cl..tw.l How are the .tare still further diatinguiabed T or 11V.-Subject T II it poable to determine the actual number the fixed starsT What is the estimated number visible to the naked eye 1 Can you give the numbers of each of the first 8ix magnitudes 1 What is the estimated number visible through telescopes 1 Cau you recite the number of eu.h magnitude from the seventh to th6 twelfth iuclu8ive 1 What is the entire number of all magnitudes 1 What remark of Dr. HeJ'8Chel1 Of ProfealOr Olmsted 1 Wbat estimate respecting the Dumber ot worlds in our firmament T How do all these compare with tbe bouDdleaa univel'88? What idea is advanced in regard to the employment. of the Chriltiau in a futore atate 1 ll8.-8ubject 1 What is the estimated tliBttJRCt of the Dearest fixed star! How lon, would light be traversing .ocb an aby.. 'l How many timea its prNent di8taJlce must such a 8tar be removed to appear only of the twelfth magnitude 1 What astonishing coDclusioDiJ follow from theee premi8e81 . l18.-Subject 1 What inference respecting their magnitutk. rrom their duttJ1ICe, 1 II it probable that the atal"8 are of uniform lize 1 What opinion prevails among utronomen respecting them 'I How many timee his present distance must our 8un be removed to trall8lDit DO stronger light than Sirius 1 How far oir would that be 'I How much I. . than the distance of Sirius1 If, then, the light 01 Sirius would equal that of our 8UD, though seven millions of miles farther off, what must be his relative magnitude and splendor 1 What does Dr. Wollaston conclude respecting this &tar 1 What is the magnitude of V~ga in the Lyre, 88 compared with the 8UD -1 Of 61 in the Swan 1 What inte.reatiDc circllrnehtnce ja mentioned reepectinK Sir John HeJllChel and Sirius1 Can)'oo give the relative li,ht ol the stan of the 1iDt six maanitudee 1 lAO.-Subject 1. What are coD8tellatioD8, and what was their origift 1 What said of their tJfttiquity 1 What proof 1 What aaid of their ft"mI(.n at fibIt 1 b there room Cor any additional conateUatloDS1 How are the coDStellatioD8 divided, or claasified 1 Which are the *odiacal? Which the nortAttn? Which the _uthem 1 What other dietiDction of the constellations? Can you name the .odiGcal con8tellations 'I What is their number 1 How many ftfWtAeTft conatellatioQ.e are there 1 Of theile, how many are modem 1 Can you name any of the northern constellations 1 What is the number of .utluna constellations 1 How many aDcient 1 Modem? Can YOQ ~ame some of the southern oouatel1atioDs1 Can you recapitulate the number of coD8tel1atiou8 in each divi8ion, and the total DIlIDber-r What is the total Dumber of priDcipal .tara 1 [Thls nu.mber itt 1917 QUESTIONS POR BXAlIIIfATION. 239 1e811 tban the· number given u visible to the Daked "ye, in the table 117; bot one table includee only the "principal" starJ, while the other embracee all that are " tMibk."] , A1,-Subject 1 Upon what ael. is the student to trace the constellationa? How are the zodiacal coD8tellations arraoged 1 How may A1V• .,. known 1 How find Tau"" 1 What &aid of the largest Btar in this coustellation 1 What are the H !lade8 ? Of du.--ir arrangement 1 How may' 08'lnini be known 1 What said of Cancer 1 For what distinruiahed 1 For what is Leo remarkable 1 Wha t iI the -.flle, magnitude, and p08ition of bis largelt star 1 In whl1t manner are his other lItal'll arranged, and where, ill tbis arrangemeot, is Regulus 7 What other aar i. named, and what itJ ita magnitude aud position 1 Deecribe the next constellatioo. What star is named, where is it round, and what ita magnitude 1 What said of the remaining atara 1, How may Lilw. be known 1 What constitute the beam of the ecales 1 Where is the 8mallest ot the four 8tars 1 What said of 8ctWpio? Of his head 7 Of his relation to the ecliptic 1 What star is Damed, and what laid of its poaition, color, lind magnitude 1 Where does Oapricorn.. lie, and how may it be k llown 1 How i8 Aquariua represented t What are the magnjtudea of hiH fOllr largest at&l'8 7 How find the le.d of the figure 1 DeflCribe PiSCN, their position, number of 1tarB, &c. Whe~ is the largest star situated, and what is ita fUJme and 1IUJgflitutk ? • • UA.-Subject 7 Where do we begin this review, and in what dir6ction do we proceed 7 How may Andromeda be known" Describe the figure. What said of the middle star 1 Of the one ",Nt of Mirach 1 Of the e.'~m one 1 What aaid of the position of Mirach in respect to the CoiOles? What of the Bize of the three principal atan 1 Of the girdle of Andromeda 1 What directly Boutb of Mirach 1 Where is Per-,eu lituated? Wbat is the figure" Where is Algol situated, and what is ita magnitude 1 What star eut of AJgol, and how far 1 What other Itam are mentioned 1 What i8 the figure of Au.riga, his posture, and position 1 What said of his principal &tar 1 Where situated, and how known 1 ,\\'here i8 the L:Ju •• tuated, and what said of ita component stan 1 Of what is Leo Minor composed, and where sitaated 1 What said of CO'11&G Berellice', its situation, and principal star? What of Charles's Heart 1 What is the figure of Bootee 1 What 18!P star in thi8 cODBtellatioll, bts magnitude, IituatioD, and oolor 1 What 8aid of his "IOUS 1" What other principal 8tar8 in Bootes1 Where is The Crown situated 1 or what doe8 it 00D8iat 1 What ill the poeition, rDllgnitude, and name of the largeet aar 1 How elae known 1 Where i8 Herculee situated 1 What the figure? How placed? Describe tb is constellation. Where i8 OpkiucAu, situated 1 D~8Cri~ the figUl e. What constitute the Mad of the serpent 1 How trace the folds of the I8rpent 1 What ia the ume auld mag'I.itaM, of the P!·.uc!pal IJtar Ie , 240 BLEKBKTABY ASTBONOKT. th. conatenatioD 1 Where is it BitoaW 1 For what ie Aq'J.iltl eonapicU0U81 What ia the po.tion, flltJgnitutl~, and appelJr.nee of ita prineip~ star 1 Where, with respect &0 the Eagle, dOO8 the conetellidion A.tinou8 lie 1 Where is the Dolplin aituated, and bow may he be known 1 How is Peguue situated, and how dNCribed 1 How may he be known 1 What said of their magnitudes, &e.1 Where ill the Hor.'. Head .tuated, and boW' deacribed 1 What CoDltellatiolUJ are Den to be coll8idered 1 Where is Ursa JliftIW aituated 1 Of what doee it coD8iat 1 In what form are til" .V~D prillcipal .tan arranpd, and where is the Pole Star 1 How lDay UrM ltIfJjor be known1 How many.ara in the Dipper 1 What part of the Bear do they conatitute 1 Can you Dame any of these 8tara 1 For what is Jli.ar remarkable 1 Which are tbe Pointl!r8, and why 80 callE'd 1 Where doee the le"d of the Great Bear lie, and of what compoeed 1 What aid of hill feet' What said of the .zteftt and 8itutltion of Draco 1 How may he be traced 1 By what may hie "'~tltl be identified 1 W-hat ill the magnitude of hi. principal Ital'lll Where does CepAeu lie 1 he any coaspicuous stars 1 Deecribe the figure. How is CtUriopritJ repreaented, and how situated 1 Of what ia ber eluJir compoeed, and what are their magnitudes 1 For what is Lyra distinguitlhed 1 Where lituated 1 What is ita principal star called '1 What. ita magnitude" What other atara in this constellation 1 Where iI Cyg"," situated 1 Deacribe ita princip.1 atara. Give the ntlme, place, and magnitude of the largest oi the group. What said of the remaining stars 1 Where is CameloptJrdalra .tuated 1 What 8aid of its chllracter 1 or ita principal 8tars 1 Where is ita h~(Jd situated 1 or what is the Lynz. composed '1 Where situated 1 I ts three largest stars are how large 1 ft""", au U3.-Subject 1 What general remark respecting the southern What is the comparative magnitude of Cetru 1 Where' situated 1 How placed 1 How may hi' Matl be known '1 Give the name, place, and magnitude or hie lalJest star. Where is Orion, and what said of bim 1 What i. the figure 1 How many principal stara 1 What stan form the ahoultler.? The IuJatl ? The 6elt or "bands 1" What other Dame have they, and why 1 What cOll8titutes his tnDortl '/ What are the belt and sword together 8Om6times called '1 Which star is called Mintiktl, and near what is it situated '1 Where is Rigel, and what his magnitude 1 Saip", and his magnitude 1 Where may upru be fouod, and bow know u '1 What is t.he DaDle and magnitude of his principal star 1 Wllere does . the Do". liel How many visible &tara 1 Name the brightest, and Dext brightest, and give their relative positions. How may Bet. be IlDOWD 1 What i. tbe direction of Eritlanu? Its Jellgth 1 How dividAd 1 Where doee the southern begin and tennlllate 1 ['rhe "utAern stream is a continuation of the northern, which forlDs a bt1ud Dear Cetus. alld puaee off lOutheMteri7 towards the Dove, and \beD consteUatiolls 1 QUES110NS FOR EXAMINATION. 80Wl to the lOuthwest till it dieappean. 241 Rigel,. in Orioo, is in thiI ItreWD. Its remaining stars are mostly of the third magnitude.J Where is Cani, Major situated 1 How, fouod? What said of 8iriUIJ 'I Where may Can;" Minor be found 1 What principal &tara, their narnes, and. magnitudes 1 Where is The Unicorn located 1 What is the magnitude of his principal stars 1 How may his head' be found 1 Where may the head of Hydra be found, and how known 1 What star in his heart, his position, and magnitude 1 Where is Th. OrolD situated, and how repre8(llnted 1 What number of visible atan, and th~jr magnitudes? What said of .Argo N a,,;" 'I How situated 1 - How known 1 Where is the star Mflrkeb 'I ,What atars of the second magnitude 1 What of the first 1 What said of CentaurU8 'I Of Lupru'l Where is 8e~taRl'l What is the size of its larpst star, and how situated 1 What laid of TIuJ Or088'1 Ita situation, aDd componena stars 1 i8 the subject of tbis cAapter 1· or thi8 le,1IOft 1 What meant by double, triple, and multiple stars1 What other Damell for the lame things 1 In what two ways are stars auppoaed to be rendered double 1 Are these companionabips more frequeni than could result from accidental causes? What does Fig. B reprellent 1 What said of their color and m.itudea 1 Why an interest· illg double star 1 What does Fig. C repreEM\nt 1 What said of the color8 and magnitude8 of its component sta1'8 '1, What is their dllttance from each other 1 What does Fig. D represent 1 Their magnitudes 1 Distance apart 1 Their color. 'I What said of this Btar ~ a te8t object 'I Of what is Fig. E a representation 1 What is the color of these stare 1 What their magnitudes, and distance asunder 1 What estimates have been made of the number of double sttr.lB1 What first led asirGnomers to 8UBpect the physical connection of double stars, and their periodical revolution 1 - JJI4.-What UI.-Subject 1 What are Binary 8'!J8tt'fM 'I How were their revolutions detected 1 What &aid of the periods of thOle best known 7 What double star is mentioned, and where found 1 When first noticed 1 What is their periodic time 1 Their angular motion 1 What curious calculation has Dr. Dick respecting these stars 1 What system is represented at Fig.- G 1 What is its probable period 1 What does Fig. H represent 1 Can you give their period, color, and mag"ituae, 'I In what light should these systems be regarded 1 What eays Dr. Dick-of them 1 What said of their proper motions in space.? What is the supposed cauae of the variety of colol'l they present 1 II it probable that the 00101'1 are merely Complementary in all casea 1 What said of isolated red st&r81 are 1A8.-Subject 1 What "ariable 8tara'l What ia the caaraCler of their variation 1 How is the term " period" applied to variable atara'l What two relDarkable periodic stars are mentioned 1 Where , 242 • aLBXBKT.BY ASTBONOMY • is .ir. lituated 1 What laid of its variatioD81 Where is Alpl' What laid of ita variatioDl1 period, color, &c. 1 What is the suppoaed • .,. of these periodic variatioDs1 Wbat _ys Professor Olmsted 1 What other theories to account for these variations '1 What remarb by Mr. Abbott" UV.-Subject 1 What are tmaptWary .tGr. 1 What aid of Hipparchua'l What of the temporary star of 3891 Of that of Nuvember, 15711 What remark by Mr•. 8umufJilie 1 What obaervation by Dr. Diele 1 What opinion by Prole.sOT Vinee? What ~ay La PlGce, and Dr. Goode 1 ",,-Subject 1 What Rid of introducing tbis subject here 1 What are the falling or shooting stan1 When great DUlnoom fall, what are they called 1 When did &Il.e most remarkable of theae occur, and bow deecribed 1 From whence are theee meteors 8Up~ed to come, and how ignited 1 How does Profeaaor Olmsted account 10r them 1 lAIt.-Subject 1 Give the ftt.lfM. and "lGce, of some o( the For what sometlmes mistaken 1 What list haa been formed, and what said of." Now known to be cluteT8, and uot t:OfMul Wbat said of the ffJ't"'fM of tbeee clustem1 What said of the Bomber of Btar8 tbey cootain 1 What said of Fig. I, and of red ItaJ'II q What aid of the probable nature and tl;'tance, of tbe indl'Vidual atara of theee clusters 1 What does tbelr globular figure indIcate 1 What fwther aaid of J and K 1 Of a new cluster 1 cJ.Q8te1'8. 1IO.-Subject 1 To what is the term MbuldJ applied 1 What are re.l"tJble nebulm1 What ifTeaol"able 1 18 it likely that any DeboIe are actually irreeolvable 1 \yhat evidence from Lord Ra.e'8 observatioD81 Where is the newly discovered .piral nebula situated 1 What resemblance to our Milky Way 1 What does this nebula reI18mble 1 Is this, too, composed of illdividual stars 1 Describe Fig. L on -the map. What said of 8inglt and double nebulm 1 What epecimen given, and where found 1 What specimen of hoUow 'nebu~, and wbel'l found 1 Wbat are ,tellsr fU!bul~ 1 What specimens, aDd where found 1 What laid of the 8un and .odiacal light? Whlit are plt.lnett.lry nebultB 1 What said of their magnitude ? What 1I1ustrative specimen 1 What tLl"e annular nebulre ~ [8ee annul.., in the Appendix.] Where may the most conspicuous be found, and how described 1 What d061 Fig. R represent 1 Fig. S 1 What does }'ig. T represent 1 What said of the nU1nber of nebuJm? What is ".tar dU8t 1" IIIUltrate appearance by the map. What iIlusUa. tion of the UBe8 aDd powem of ibe telescope from this map 1 What is the object of tbis experiment 1 What says Sir John Herschel of the uebule 1 What said ot the Milley Wt.ly 1 How iIIW1trated by map 1 Why, theu, appear 1M) extended 1 How would it Ilppear'to J . • 243 QUESTIONS FOR EUMIN A.TION • an oMerver II far off 88 the nebub., in the Lyre 1 1\la1, thereCore be called what 1 What is Madier's conclusion in respect to the structure of our stellar firmament 1 What estimate by Sir W. Rep. schel relative to -the numbw of the fixed stars 1 What said of then probable mutual distance" positions, and offices 1 What idea of the enent of the univerae drawn from the dimensions of our own cluster. and the number of clusters in remote regions? What closing re1leotioDs are subjoined by your author 1 • • / • .s ••. HUNTINGTON AND SAVAGE, RL 8'1'8111ft', . ."" 'W'OBK, PUBLIIU TilE POLLOWDIG '-.~LUABLE SCHOOL BOOKS. To which they very relpectfull, solicit the attention of County and 1'ownl IlupenoLenuents, Trulleel, School CommiUeel, Teacbera, and others in1.e.roMed in the cause of edu.catioD. . . AN ELEMENTARY ASTRONOMY. 'lor Academies and Scbools. Illustrated by numerous original oolonMl dlagralos. Adapted to uee witb or witbout the author's Large Mal& By R. MA TTI80N. Fifth Edition, with QuestioDa and a Glosnry. This is one of the moet comprebensive and splendidly illustrated wora OIl Astronomr that has ever been published in the United States. Its plan iI eminently onginal and philosophical. It il collfined to the fACt. of the act. ence, or the res.ltB that have been reached during the lapse of ages, Ytithou& delineating ita Mythologi(~al history. or tracing tile processes by whicb theae facti have been 8scertAlnp.d, either by tbe use of instruments, or by mathematical calculatioDtl. It embodies all the late discoveries, and is equally adapted to private Jearners. the library, and the schoolroom. 88 it is complete in itself, independent of the large charta. As a book of reference it it iDvaluable. To this may be added its perfect adaptation to use Mlit/a the larre Mapa, (of whicb the illustrations in the book are exact copies in miniature,) ., that tbe learner baving the Maps. baa on a large scale the same dia~ by which to illustrate the lesson at the recit.at.ion. that bave been preViously Itudied by the pupil in the text-book. To say nothing of the recommeJlda. tions that follow. the sale of ta tA"..aJId copies of this work, in a little OV8f a ,.,., iI a sufficient proof of ita popularity and intrinsic value. ASTRONOMICAL MAPS, ~pted to ulle with the " ELBIIEICT Aa y ASTao.oIlY." and de~igned to jl1ue&rate the Mechanism of the Heavens. For the use of Public Lecture... Pri vate Learners, Academies, and Schooll. By H. M.TTISON. This series eonsista of Sixteen Maps, or Celestial Charts. eflch 38 by oM IDches, representing the various appearances of the Heaven]y Bodies-th. Bun, Moon, Planets, Cometa, and Fixed Stars-and illustrating the lawe which govers them in their motions, the philosophy of Tides, Eclipses, and Transits, and indeed all the most interesting and wonderful phenomena of &he Mechanism of the Heavens. 1'be sixteen Maps cover an area of nearly 100 8Qwne feet. They are printed upon a black ground, answering to the Ilatural appearance of the heavens io the night, and are beautifully colored and mounted upon slats and rollers. They are beyond comparison the m08& Iplendid and complete eeries of scientific charts ever published in this couotry. They are not only invaluable for Seminarie., Academies, and the higher inltitutions of learning, but at the same time are admirably adapted to popular use in Common Schools. 0... tAouarul .d8 of this work have already been IOld and gone into use in different parts of the country; and the unaDimity and cordiality with which they are commended by aIL who have us~ or examined them, i6 truly graufying to the publishers. (See fo~owing page.) MAPS, per set, in case, with cloth backl, •.....•.................. $20 00 on 8trong papel, without cloth backs. 15 00 Books per copy J • •••••••••• • ••••• ••••• • • •••• •• ••• • •• •••• •• ••• • • • ••• • • • • 50 " U " ~ Each Set of Maps is nicely packed in a Wooden Case, lind can be I8Ilt La order wi~h perfect safety to any pan of the Unlt.ed States or Canada , ------------------------------------------------The attention of 8upm"tend~"t,· of T.fJcl&er., U re~ctf'ldly 8clwoZ" Tru.tt•••, tJtttI i"mt,4 to IAe /ollOfJlifw RECOMMENDATIONS Of the .. Blementary Astronomyt" and Mapa." II MtroDOmleal Having examined, aDd aeveral of 1J8 UIed, the EUDNTAlty A... and AITa.ONOJlICAL ~AP8, by H. Mattieon, we are prepared to say, that in Olll opinion, they are better adapted to the purpoeee of ~Iementary ill8truction in Astronomy, than any other work or apparatus now before the public. We would therefore cordially recommend their introduction into all schools where this sublime lIlieuoe ia taught. TRONOMY EDWARD COOPER Sec'y of Teachers' A88OCiatioD, state N. Y. ALBERT D. WRlGH'!:, Principal Normal !nst., Brooklyn, N. Y. lAS. L. McELLIGOTT, Prine Col. Scboc:!!t N. Y. city. JAS. R. BOYD, Prine Jefferson co. Inst., watertown, N. Y. R. K. SANFORDt...Teacher Natural Science, Middlebul'J AcadelDJ. Wyoming, N. Y. N. BRITTAN, l'rincipal of Union School, LY~DI. N. Y. R. F. HICKS, County Supt., Livingston co., N. Y. ALONZO BEEBE, County Supt., Ontario co., N. Y. HENRY GILLAM, former teacher of Math. Cayuga A.cademy, N. Y B. R. McALPINE, Supt. of Public School!t RoChester, N. Y. ELLERY S. TREAT, Prine .Pub. School .1"140. 1, Rocbester, N. Y. WM. BARNES, " " ,. 6, " A. F. HALL " u " 7, " REUBEN JOHNSON, U " "I, " DANIEL HALLOCK, .. ." "11, " A.. 8. GREGORY, " " "14 " H. G~ WINSLOW, Prin. Union School, Mount MOrril, N. Y. 8. P. BARKER. Prine Public School No. 10, Brookport, N. Y. G. L. FARNA~) Prine Public School No.3, Watertown, N. Y. G. R. JACKSO.N, Teacher, Oswego, N. Y. 1. PATTERSON. Prine Public Scllool No.4, N. Y. city. JULIA B. CLARKE. Teacher of Public School No.1, Oswe,o, N. Y. Prom Plto.. Ml'I'OlIJ:L, Dir,ctor of tie Citu:tftfUJti OHerN,.,.,. In a note to the publishers, Prot: M. saye: " Your series of Maps are hung up in the public reception-room of the observatory. I am much pleased with your plan 01 speaking to tile ey~; aud am confident that these maps will lOOn fiad their wal iP..o every well-conducted schooL" -- 16 THE GEOGRAPHY OF THE HEAVEN& AND CLASS-BOOI[ OP ASTRONOMY. I wL 18mo. ~mpaDiecl by • CeleRial AUu, imperlal4to., aeady colored. . . admirable work to follow the" BL.M.wTAa., AI,.aOllOMY" AIID .. .&. "aONOMIO.a.L M.a.,•." The two works together preaent a more thoroua embodiment of the leienee than any othel'8 of the lame compus, in die country. COXT.WTS 0,. TRW ATLAI. 1. Plan exhibitiq the relative Magnitudes, Distances, aDd Position of tbe . different Bodies which compose the Solar SY8tem. I. The Visible Heavenl in January, February. and March. a. The Visible HeaveDs io October. November, and December. 4. The VIsible Heavens in July, August, and September. O. The Visible Heavenl in April, MIlY. and June. I. The Visible Heavenl in the South Polar Regions, for each montb ta the year. T. The Visible HeaveDl in the North Polar Regions, for each month ill the year. L PlaniBphere of the Whole Heavena, on Mercator'e Projection. B., E. A. BURRITT. A. K. With .... Introduction by THOIU.. DICK, LL. D., Author of the "ehri.tum . Philoaopher," written expre181y for this work. A .-ariety of interesting facti and obllervationa, embracing the latest im.. provements in tbe science, were derived directly from the French and EDJ.. lish Observatories, ,..,••Z, for this Clas•• Book1 and are not contained m an! other. It is now comin8 generally into use In our principal SemInaries, ana' il recommended to schools in general by membeJ'l of the Board of Examination of Yalp College, as a work more needed, and which, it is believed, will be more useful than any other introduced into our " Instituti0D8 of Learning, for a number of years." This book, as its title importa, is deligned to be to the starry beaveu what geography is to the earth. Such a Clase-Boolt hae looe' been needed. Hitherto, the science of the stars has been but very superfiCially st_died in our schools, for want of proper helps. They have conunued to gaze upon the visible heavens without comprehending what they saw. They have C8!i1t a vacant ere uP.t!n the splendid pagel of that vast volume which the Bight unfolds. as ('hlldren amuse themselves with a book which they lU'8 unable to read. They have caught, here and thero. as it were, a capital letter, or a picture, but ther have failed to distinguish those smaller charaotera. on whIch the 88D8e of the whole depends. Botb teacher. and pllpll. have found that Class-Books and Maps are as mdispensable to this department or knowledge, as to that of Geography; and that an artificial globe ie just as poor a substitute in ODe case al in the other. Instead of the globe, and a few balls strung upon wires, Mr. Burritt's book Bnd Atlu introduces the pupil at once to the Grand Orrery of 'he Heavens. and makes him acquainted with the namel and positions of the bodies which compose It. He learns to locatf: and to cllunfy liis astronomical knowledge as be does b:i8 I8Ogrftphical; and experience has proved that a child or ten years will trace out all the constellations that are visible 1n the heavens, and name the principal stars in each, lUI readilyal he will learn the bt)unciariea of U. ata&e8 from a map. and I1&ID8 tb8 citie. they contain. Huntiftgton 4- Savage's Publicat 'OM. 17 . ----------------------------------------------------~ A NATIONAL 8EOBRAPHY FOR- SCHOOLS-, IDUitrateci by ao Engravings and eo Stylograpbic Maps; with a colored GLOB. MA.p, OK • Raw PLAa. • One vol. qu.rto. 1 New and improved edition. By 8. G. GOODRICH, Author of Peter Parley's Talel. I This work il designed as a .eAooI-boo~a manual for ',ocli",; and notblDl In the _ "rlt is allowed to interfere with this delip. At the same time, from the arrangement adopted, it will be found to contain a great quantity of Qlatter which will render it a convenient family book for reference. Ita utility, in this respect, will be enhanced by the index at the close of tbe Yolums. Biwa,licity, ".,.~, and con",,"-c, haye been carefully studied in the arrangement of the wbole wor~ Thus the typography, especially tbat w bien contains the leading ideas" of each lesson, IS clear and conspicuous; the letteriIlg of the maps is peculiarly full and distinct; the whole view of each country is brought together, so as not to embarrass the reader by ... referenee to I8parate pages or separate tablel; distinct ma~ of tbe prla cipal countries are given, and care bas been taken not to fill tbem with unimJM?rtant names, whicb may bewilder the student, nnd render all his acqwsitiona obscure and imperfect. Too many of the popular achool-bookl on this subject are made to complUJl two oJ?j,ct. j to combine a univel'BaJ pOfrapb1 and a school geography in one. Botb objects are not, therefore, wei attained, for while there 11 not enough for the former, there is too much for the latter: the eonaequence is incoDYenience and embarrassmeu& to the teacher-increased study and labor to the pupil, whUe be is imperfectly instructed, if not actually injured in his habits of study. Tb6 mBpa and text of this work contain quite as much 'of detail 88 the pu~il can remember. Tbe design has lMten to embrace just 80 much, that, If well studied, the pupil will carry in" his mind olear amd diatinct images of tbe forma of eountriel, courses of rivers, location of toWnI, cities, ~., 10 that every country, with ita lead.iDi featurea, can be and- will be permanentl, mapped on his mind. In respect to ma~ a new and useful device has been adopted, which we entitle a Globe JIG,. This, of neceSlity is separate (rom the pages referring to itl but its great utility and convenience, iD the way it is to be used, cannot raiJ to strike e1'erY practical teacher. It has a handle, and with a tIIOtW oj tM 8wh. in AU 1&tbi4, the pupil is taught the various names given to the divis\ons of land and water, the shapes of oceans and continents, and the relatn'e positions of countries and places upon the face of the earth. It is, in short. ~ ..,h.lit." lor "" GrtijiciGl 6'1obe. With the advantage of being toasily handled, and collltantly before the eye, during ,the early stages of the study. As Il means of rendering the progreSl of the pupil at once agreeable and eft'ective, the author haa- endeavored to invest the subject with every tiegree of interest of whicb it is capable. He has sought to keep the attention _ ilive by vivid descriptions; and, in order to convey accurate Impressions of Visible objects, he has introduced a larger Dumber of illustrative engraviugI than have ever appeared in" similar treatise. Everyone knows that mere wordl are incapable of conveyi~ correct and distinct ideas of a.nimals; am! that a simple cut of a lion, for instance, will be more useful in gl vinK an impression of his (orm and aspect., than a whole volume o( verbal deICri'ption. The same may be said 01 the countenances and costumes of 1'&.1OUS nations; of tbe peculiar mQ<ies of building, travelling, worshippiq, b. The engravings, therefore, are not introduceC:l aslnere embellishmenll ID4 allure menta to the pupil, but. U all emdent. and euentlallOurce ot cor ... iDlormatMm. Huntington 18 4- Sawzge'8 Publicatiou. PETER PARLEY'S NEW GEOGRAPHY FOR BEGINNERS. with 18 beautifully colored Maps, and 150 Engravings, aDd DeadJ bound in stil" covers. It were needlea to speak of the felicity of style, or of the simple~ clear, and practical method in which Peter Parley presents to tile young the subjeCts of which be writes. Notwithstanding other workl of the kind baye been issued. tbia little work, more full and accurate tban any, continues to make its way in all places wbere improvements in primary education are ,oing forward. It bas been reprinted in Eagland, and is extensively uaed througbout that country and Ciwada: it haa been translated into French and is much used in France; it baa been publisbed in Greek, and introdu;;! to 10,000 youth of that nation. It bas alao been translated by the missionanee in Persia, and introduced into their achooll, and has been more recenti1 reprinted in Sidney, New South Wales. This foreign use is evidence 0 the yalue and popularity of the work; yet it is to be regretted that we have DO oopyn.ht law to give authors and publiab\rs the beneAt of such uae. InUl~tecl FAMILIAR LECTURES ON BOTANY, PRA.CTICA.L, ELEMENTARY, AND PHYSIOLOGICAL: With a New and FuU Description of the Plants of the United States, aad Cultivated Exotica, &c. For the Use of Seminari88, Private Students, and Practical Botanilt8. By MRS. A. H. LINCOLN,-Row MRS. PHELPS, .BllfCIPAL 0,. THE PATAP8CO ,.• • "'L. IK8TI'I"O'l'. OF M.aYLAIJD. New Edition, re.iaed and enlarged. 1 voL imperial lImo. In the present edition of this work, in compliance with the request of man, teachers, the "Descriptions of Genera and SpE!cies" are DOW made to include all those native and foreip/laDts which the pupil will be likel,. to meet with in any part of the Umte States. The author has been anXlOUI not to omit Southern and Western plants of any interest, and large additionl wlder this head have been made. Should teachers, or students, observe such omissions, communications on the subject, made to the author, would be gratefully received. The author has now tboroughly revised the de8Cri~ bOilS of plants. For the numerous additions made she IS indebted to several Am£rican works, especially to tbe "Botany of the Northern and MIddle States," by Dr. Beck; and also to the descriptions of Torry, Bigelow, and Elliot. For foreign plants, Eaton'llLIld Wright's Manual. Withering's British Plants, Loudon's Encyclopedias, and some other works, have been CODlulted. For cleamflls, simplicity, and philosophic predsionJ there are few schoolbooks which hold a more pre-eminent rant than Mrs. J.,inooln's Botany: few certainIf have a wider and more justly deserved popularity. The work ia divided Into Foua P "'BTS1st. The Analysi~ of Plants, or Lessons in Practical Botany. td. The Organs of Plants, beginning with the Root, and ascending to the Flower; or what is termed ELBMBNTA.BY DaTA-NY, and Vegetable Pb,-10 logy.: 3d. The different Sy,tftU of Bot""" and the most impoltant NGtural r .... 'k.; the mOlt interelting genera and families found under each Clul aDd Ocder. 4th. The progreaiY8 appearance of Plowers in the SeUOD of BloomiDl: &he Phen~mena 'p~u~ by the cWferen& fiateI of J4ht, A&moapbere. &0;. • Ueo,rapbical DilUibutiOl&. " Huntington 4- Savage'8 Publicationa. 19 Hi~torr of Botanical SCience, and tne Analogies and Contrasts betweeli organized a.nd unorganized matter in Nature. A distinguished and experit-nced teacher in natura) science says of tbu work :-" Far from depreciating other ..,arks on thi~subject, I think my remark will not be invidious, when 118Y, that I think it far better adapted to the purposes of Eleme'otary Instruction in the science than UD)' I have seen. I am much delighted wit.h'the easy and natural method by which it intro. duces the scholar to a knowledge of the first prinCiples or the science, IUlti the strict philosophical arrangement it employs in imparting instruction. Tile whole work has the impress of one practically acquainted wit" the aJ"l of teaching, and adds another proof to the many already existing. that illoItru('Lors of intelligence are generally better qualified to prepare elementary works than those who have never had any experience in the businesa Of leaching." f BY TH&.fAM& AUTBOIL, DESIGNED FOR PRIMARY AND COMMON SCHOOLS, BOTANY FOR BEaINNERS. AJf DTlLODUCTIOlf TO ..... LINCoLN's BOTAlfY. By MRS. LINCOLN PHELPS. 1 vol. 18mo. pp. 150. This book is intended chie8y for the use of primary ecbools aDd the younger pupils in higher schools and seminariell. So much baa, of late, been urged by thOle who take an interest in the subject of education, in favor of introducing the Natural Science. into Common Schools, that it ill to be hoped that the time is not far distant when plants and minera.ls will be as familiar objects of study in our district school-house as the spelling-book DOW is. Perhaps some parent or teacher may be ready to inqwre. whetber it is recommended that such studies shall take the place of reading, spelling, or writing; by no means; but every teacher knows that there are many listless aod vacant momenta when even the most active of his pupils oseeza tired of their monotonous I!ursuitl; habit and rest»ect for their teacher ma, lead them to sit still and do no mischief; but it 18 not difficult to perceive, ~y the heavy eye and inanimate countenance, that the intellect 81umbera. These are the moments when the experienced teacher feels the need of some new stimulant. Instead then of saying, "John, or Lucy, 1,0u hal·. been sitting idle this half hour, wby don't you mind ,our book l' he who understands the human mind is aware that this 11 the very W&Yltill more to . disgust his pupil, and he will assuredly be read! with some new met.hod of awakening attention. Suppose, then, instead of a rebuke for idleness, the teacher sbould kindly addresl his pupil as follows! "You have been 10 10D, engaged upon a certaiD set of studies, that I perceive ther have become ti.... lOme; I think of introducing a new:study into the schoo ; to-morrow I,laall II uctur, "" Bo'.,; you may therefore briD, with you to-morrow aU tne wild lilies, or violets, or any kind of common wUd ftower that you can find in the fields." The eft'ect~anyone at all accustomed to the care of children will readily understand. lIut it may be said, "there are many teachers who are Dot capable of giving a lecture UPOD botany." To this it may be an.wered, that every teacher who ia in any degree fit to be .uch can use tb. "Botany for Begmners," evell though they never heard a lecture upon the aubject of botany; it will teach him the leading principles, and he can explaID them to his pupils; this will be ucluriftg Mpoll BotMY. Thousands are usmg this, little work, and give the strongest testimony m it. fayor. The succeSlOr of Mils Beecher in the Hartford Female Seminary say. :.. It Ja 11 clt'&(, simple. and interesting exhibition of the princ:plel or RU 8D o "fie 20 Huntington.4- Savage' 8 Publical:um8. tertaLming lIJCience, adapted to the comprehension of children, for w hOD - . de81gueu. and Cully capable of preparing them for a more extended trea It 11 partIcularly recommended ~ the instructor. of our common IChool.. f A an interesting employment for tbe leisure hours of their scholars; u . .~ mothers, WI an US1StaDt to them in th, great work of storing their chil~ IDI.UJa With the &Dowledge of the woro of their Crea&or." t, PHELPS' NATURAL PHILOSOPHY, i'O& TH& ua& 01' IOBOO1.8, ACADJUD&a, AND PILlVAT& ITUDUT& Illultrated with numerous EngraYings from ofisiDal desi8MBy MRS. LINCOLN PHELPS. New Edition. I voL limo.. PHELPS' PHILOSOPHY FOR BEGINNERS. 1 yolo IS.o. A teaeher of much experience, and Principal of one of our firBt Acad.emi_ UI1,.I of tbese work s ! . 'The 8ubject is treated tn a manner highly scientific: the enp1lvinp d.8lrigned for illustrating the text are bappily chosen and executed; and a delTee of freshnel8 pervades tbe whole work which cannot but impart life and animation to the t1tudent of its pages. But more than all, we rejoice to_ -' healthy moral feelmg di1I'using ita fr~rance oyer the wbole." PHELPS' CHEMISTRY. New Edition. I yolo limo. PHELPS' CHEMISTRY FOR BEGINNERS. 1 yolo 18mo. ProfessoT Caswell, of Brown University, baving examined some of the DJ08t important chapter8 of these works, saY8 :-'i'~ _The principle8 of the science a~pear to be stated with brevity and clearneu, and are h8ppily ill. . t.rated by CamiJiar and well-selected examplel." UlfIVBBSITY BDmOB 01' DIL WEBSTER'S DICTIONARYI Abridged from tbe quarto American Dictionary, with Walker's Key to the ProDunciation of Greek, Latin, and Scripture Pro~r Names, etc. With a Memoir and Bust of the Author. 1 voL royal duOdecimo. 556 pageL WEBSTER'S HIGH-SCHOOL DICTIONARY. limo. 3GO pagel. The design of this volume is to furnish a vocabulary of the more common words, which constitute the body of our 1anguage, With numerous technical terms in the Seiences and Arts, and many wQrds and phrases from otber languages. which are often met with in Engliih books, with a brief definition of each; to which is added an accented vocabulary of CLASSICAL, SCRIPTURE, and MODERN GEOGRAPHIC NAMES. The Ortbosnp~y and ProDUDciation .are made to correspond closely with those editlon. ot the work of the author recently rensed under \he editorship of Profeuor GOODRICB, of Yale College. Huntington ~ Savage's PUJ.. WEBSTER'S PRIMARY SCHOOL PIONOUI With Accented Vocabularies of Clasaical, Seripb phical Proper Names. Square 16mo. New \ larged, corre8}¥)nding in orthography to the lar. ' This work embraces about ten thousand more wot- . Dictione:ry, and is especially recommended to the at, .Also-POCKET EDITION, in several stylel of bin" and gilt embosled. . 0"" ;. .. Thil last is a vocabulary of the most important word" both common and scientific, with a concise, primitive defin~ .. word, followed by the derivations of the same word,-thus pres~.. _~_ two features in one, of a defining Dictionary, and one of the Synonyms. The following Testimonial is subscribed by a large number of the most distinguished men of our country: " The subscribers highly appreciate Dr. Webster's purpose and attempt to improve the English language, bK rendering its orthography more simple, • regular, and uniform, Hnd by remOving difficulties arising from its anomalies. It is very desirable tha.t one standard dictionary shdUld be used by the nu· merous millions of people who are to inha.bit the vast extent of territory belongin, to the United States; as the use of such a standard may prevent the formatIon of dialects in states remote from each other, and impress upon the language tmiforaity and atability. It is desirable, also, that the acquisition of the language should be rendered easy, Dot only to our OWIl. citizens, but to foreigners who wish to gain access to the rich stores of science which . it contains. We rejoice that the A...mcan DictUmary bids fair to become Inch a standard; and we sincerely hope that the author'S elementary books for primary schools and academiel, will commend themselves to the general use of our fellow-citizens." THE PRACTICAL FRENCH TEACHER. " NORMAN PINNEY, A. ~. The leading peculiarity tn this work is, that it exercisel the studen~ throughout in the constant practice of speaking. The preparation of every 1es80n is a preparation for speaking the ianguage, and every lesson is an actual conversation in it. These conversations. too. are progressive and I1stematic ; commencing with the simplest elements of the language, and advancing by an easy process, to the more ditlicmlt. The wbole has been prepared with a view to overcome the difficulties which an American meets in acquiring a knowledge of that 10 necessary part of a finished educatioD. KEY TO PINNEY'S PRACTICAL FRENCH TEACHER. THE FIBST BOOl[ Dr FIlI1WOB; or, A' PrRctieal IDtroduetion to the Reading, Writing, and Speaking of the French Language. By NORMA.N Plln.BY, A. M. PICTORIAL PICTORIAL PICTORIAL Pl~ORlAL PICTORIAL HISTORY OF THE U. STATES, ~y S. G. GOODRICH· HI~wroRY OF FRANC~" by S. G. GOODRICH. HISTORY OF ENGLA1~D bJ S. G. GOODRICIL HI~RY OF ROM~J.. by ~. G. GOODRICH. HI8TORY OF GREu.;E, by 8. G. GooDRICH. The above series of histories, formerly p'ubJisbed by Mesars. Sorin k Ba)). of Philadelphia, is very extensively introauced into both private and pub1i4Institutions througbout the Union. 20 u: . aU~~~ 1&.4- Sa'Oage' a Puhlicai:um8. ________________________ __ . ada t"O# MECHANIC', COMPA.NION I IiClence, p",. deslgneo. and Cully caps.): of 8uper1lces and Solids i tables of Squares aad It ~ partlr.~arly r8CoDlDlube RoOtI; Circumference and Areas of (...'11'01_ • all mLerestmg employm·.l Powel'l; of Steam and Sleam Engines ; mothers, as an aaalstaD~ Statel Weilrhts and Meuurea- .&.• Js WIth the lwowl~ -0 -Y~. • mill :BY J. K. SCRIBNER, A.. II. E L ~Q. . . .0 papa. Morocco, &ilt. with tucka. PH tty recommended by leveral diltinguished civil engmeera roa THE UP' .Dd. as a Manual for practical mechanics, 18 a work 01 t!'~sides the general topic$ already enumerated. it contams • 11l1U!'of valuable matter, in relation to Centres of Gravity; Gravlta.. . ;diel; Pendulums; Specific Gra\1ty of Bodies; StrenJth. Welgb\. .. awl Crusb of Materials; Water Wheels, H)'dl'08tatics; Hydrauhcs ; ~t1C8; Centr. of Perouuion and Gyrati0l;l; Friction; Heat; 'rabies of WeIgb&a ul Metals; Pipes, Scantlings; lntere~kc . . . .kc.. . tartlLlnlDg • . THE ENGINEER'S, CONTRAC'foR'S, AND SURVEYOR'S POCKET TAPLE-BOOK. BY J. II. SORIBNER, A. II. 1M papI, Mmo. Tuck bJndiDl, with gilt ed,.. The above work compri8el Logarithms of Numbers, Logarithmic 8in"p.I' ul(l Tangents, Natural Sme. and Natural Tangents; the· Travene Table, Dud it full and extensiYe set. of tables, exhibiting at one Yiew the number or eu.. UIC Yards contained in auy embankment or cuttins, and for any base or slope of sides usual in practice. Belides these essential tables, the work comprlse8 60 cagel more of Mensuration, Tables, Weights of Iron, 8trengt;h of. MatefIB 8, Formulas, Diagrams,. etc., for laying out Railroads, Canala. and Curves; much of which has never before been oft'ered to the publio, and kll indispensable to the engineer. This book will prove a great saving of tUlle. and "'iii enable the new beginner to furnish relul! accurately (and .. " .. mnch greater rapidity) as the most experienced in profession, without u.aid. '1'Ile tables of lOfarithms. etc., have been care u11y corrected and C('rupared wlth different editions of the same tables; and all the tables throughout the book have been read carefully by proofs four timea; hence the moe impliCit conAdence may be placed in their correctne8L i j I ~ • I KAME'S ELEMENTS OF CRITICISM. I yo1. bo. t)- Tbe only edition which received the latest reYilion of t.he Auther. ·PRESTON'S BOOK-KEEPING, DouaLB ARD SINGLB BlfTR Y. PRESTON'S INTEREST TABLE•• \ ,. per cent.-Large and Abridged. 7 per cent.-Larp anc.l Abridged. An7 valuable Boob to he IIad lD .ewTor~ will be taaishecl b7 B." . . at the Lnred Guia Pric-. , ~J The End. World Public Library Association