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Book Reviews The Earth Its Origin, H i s t o r y and Physical Constitution Harold Jeffreys (4th edition, 1959, pp. 420+Ni, Cambridge University Press) All geophysicists will be grateful that Sir Harold Jeffreys has found opportunity to revise his classic work. Those hitherto unfamiliar with T h Emth will discover with delight Sir Harold's elegant and powerful command of the English language and of mathematical exposition. They will join the many readers who have been convinced by the arguments, amused by the chapter headings, roused by the polemics, and thrilled by the triumphs of scientific method as the author's story is unfolded. Those to whom the earlier editions are familiar will be most concerned to see what changes have been made in the Fourth Edition compared with the Third. In plan and paragraph numbering there is almost no alteration, but Sir Harold has added material from the research of the years 1950-58, including his own, on travel-times of earthquakes, and on the modified Lomnitz law of creep, with its implications for studies of the departure of the Earth's mantle from purely elastic behaviour. There are also new considerations on polar wandering, the Moon's surface features, and the Earth's thermal history. The bibliography has been considerably augmented, and includes about 700 references, in general running as far as 1956. Readers will not be surprised to find that on the whole Sir Harold continues to hold, and to defend with vigorous and lively argument, his well-known views on the constitution of the Earth's crust, mountain formation, continental drift, and the Earth's thermal history. It is easier to mention topics omitted than to list all those included. This book does not discuss the information on geophysical problems which has lately been derived from nuclear explosions and the motion of artificial satellites, nor recent work on continental and oceanic structure as deduced from widespread and accurate observations of surface waves. But in spite of the great range of modem developments in geophysics, there is still very little which cannot be found treated with insight in this book. The reader cannot fail to be impressed by the scope of Sir Harold's enquiries and the extent of his information. The arguments are close-knit, and the mathematics, never included for its own sake, is usually advanced and sometimes severe. But the text is so written that the argument can be understood when the mathematical details are taken for granted. The first edition of The Emth was published in 1924. In the second, published in 1929,a great deal of new material was included. The third edition, in 282 Book Reviews 283 1950, incorporated the results of rapid advances in all branches of geophysics, and again differed greatly from its predecessor. But the fourth edition, changed mainly in details from the third, shows that the accepted body of theory and experimental data is now large. To that body Jeffreys’s 120 original papers and books have made a major contribution. Sir Harold‘s close association with the development of geophysics over forty-five years has given to his writing, with its flair for highlighting key historical discoveries, something of the excitement of a first-class detective story. He must be a dull reader who does not catch from it some of the exhilaration of the intellectual search-and struggle which Sir Harold describes with enthusiasm, and in which he has engaged with such outstanding success. E.R.L. Physics of the Earth’s Interior Beno Gutenberg (International Geophysics Series Vol. I, pp. 240, Academic Press) Professor Gutenberg, whose death recently occurred, spent a lifetime studying the Earth, and as a seismologist was eminently qualified to write a book on the Earth’s interior. This book makes an admirable start to a new series on geophysics and should make a good textbook for graduate students. The study of the Earth’s interior relies most heavily on the results of seismological research but, to a lesser extent, draws on a host of other subjects. In these days, when the effort expended on geophysical research is so enormous, no one person can expect to have more than a nodding acquaintance with a few of these fields. Hence, there arises the need for a book which will contain all the important information from a variety of subjects and which supplies enough references to make the consultation of the original papers a relatively easy matter. In these respects, this book is very good. It is, generally speaking, well up to date with references to papers published during 1959. Perhaps it was expecting too much to see references to the new data on the figure of the Earth obtained from Earth satellites, but such subjects as radiative heat transfer, phase changes and the palaeomagnetic data collected during the past few years are discussed. A consistent feature of the book is the emphasis given to the physical problems involved, with mathematics reduced to the minimum necessary for exposition. Separate chapters are devoted to the crust, mantle and core and other chapters are concerned with the physical conditions and rheological properties of the various regions. Where the author feels less than expert, he is content to quote, sometimes with a healthy scepticism, extracts from original papers. This attitude is particularly evident in the first few pages of the book on methods of investigation and the accuracy of results. He draws attention to the dangers of using the results of investigations without a proper appreciation of their limitations. So often have the “facts” about the Earth’s interior been shown to be without foundation. For this section alone, the book deserves a place on the shelves of geophysicists. D.C.T.