Download Selected excerpts from Compton`s Pictured Encyclopedia (1927)

Selected excerpts from Compton’s Pictured Encyclopedia (1927)
Ether. You know that the earth is surrounded by a layer of air called the
“atmosphere.” But what lies beyond that, in the immense spaces between the earth,
the moon, the sun, and the stars? Scientists have decided there must be “something”
in those spaces, and they have called that something “ether.”
According to the scientists, this ether of space is everywhere. It is a substance
finer than any known to our five senses, and it extends beyond the farthest star and
penetrates even the densest bodies. It exists in a ball of the toughest steel like water
in a sponge; but you can’t squeeze it out as you can water from a sponge, for as long
as the steel ball takes up the least bit of space, it takes up just that same amount of
ether. The nature of ether is closely related to the theories about the constitution of
matter (see Atoms and Electrons).
It has been discovered that it takes light about eight minutes to travel from the sun to
the earth . . . If there were absolutely nothing along the 92 million miles between
us and the sun, neither light, nor radiant heat, nor anything else could travel
through that space. Sound, for instance, travels through the air in waves. If there
were no air, there would be no sound. The same is true of light and radiant heat,
except that they do not travel by air waves, which are much too slow for them,
but by waves in what we have called the ether. This method of travel is called
“radiation” (see Heat, Light). Certain forms of electricity also travel through the
ether by radiation (see Wireless Telegraph and Telephone). [vol. 3, p. 1180]
Light. The speediest traveler in the universe is a beam of light. In the double tick of a
clock, it can go around the earth more than seven
times. Indeed, so fast does light travel that, until
250 years ago, the best of scholars thought it went
instantly from place to place . . .
The best measurement [of the speed of light] is that
made by an American professor, A. A. Michelson of
the University of Chicago. He found the velocity of
light to be 186,284 miles a second . . .
And what is light, this swiftest of all messengers?
We can think of only two things that can travel across
space, either matter or motion. That is, we must think
of light as some fine material substance thrown off by
bodies; or we must think of light as a motion set up in
some medium. Sir Isaac Newton . . . believed that light was a material substance,
and that a beam of light was a stream of fine particles . . .
We now know that Newton was wrong, and that light is not matter.
Then how are we to explain light? Let us go back for an idea of our childhood.
The boy throws a stone into a smooth pond or pool to watch the waves go out in
circles, and these circles travel outward until they are deflected from some floating
plank, or perhaps not until they reach the shore . . .
Of course light cannot be a wave motion in a heavy substance like water. [In
1690, Christian] Huygens said that there must be a substance which is far thinner
than the lightest gas, a substance which has no conceivable weight, and so fine that it
penetrates between the smallest molecules and atoms, and that spreads through all
space to the farthest star and beyond that. This substance is the ether (also spelled
aether). The only way we can know ether is by the waves in it, which we call light
waves, electric waves, radiant heat waves, and X-rays. (see Ether.)
Professor Michelson, who as we have seen has measured the velocity of light with
such exactness, has also invented a beautiful instrument which enables us to measure
the length of light waves, the “interferometer.” . . . [vol. 5, pp. 1997-1998]
Heat. Do you ever wonder what heat really is? Perhaps it would surprise you to learn
that for centuries very learned men were puzzled by this question. They weighed a
piece of metal and then heated it, only to find that adding heat did not increase the
weight. They found, however, that adding heat did increase the size . . . [They] were
led to believe that heat was a mysterious fluid, which was invisible, weighing
nothing, but which could flow in some way from the hot body to the cold body. This
fluid they called “caloric.”
This idea that heat is a material substance was
believed until almost the year
1800 . . . Then in 1798 and 1799 two men, Count
Rumford and Sir Humphry Davy, showed by
experiments that heat could not be a material substance
...
In 1798 Count Rumford wrote to the Royal Society of
London an account of experiments that he made while
boring brass cannon in Munich for the Bavarian army.
He observed (what every machinist knows) that in
boring metal the tool and the metal both get hot; but
Rumford asked: “Where does this heat come from? What is the heat?” He insulated
his brass block by felt, so that the heat could not come from outside; then he used
blunt tools and got fewer metal chips, but got more and more heat but by using more
and more mechanical work. In his account he wrote: “It is hardly necessary to add
that anything which an insulated body can furnish without limitation cannot possibly
be a material substance. It must be motion.” He meant the motion of the particles
of the body. . . .
[In 1840] James Prescott Joule of Manchester, England, by churning up water and
thus heating it, measured in long careful experiments the work need to produce a unit
of heat, that is, he got “the mechanical equivalent of heat.” We know from Joule’s
work, which has been repeated by many others, that it takes 778 foot-pounds of work
to produce a “British thermal unit” of heat . . .
If you hammer a piece of iron it gets hot, because the blows of the hammer give
motion to the molecules of the iron. You rub two dry sticks together, and under good
conditions you produce heat—that is, you set the molecules in high motion, so that
the wood catches fire. To explain heat, we must remember that all matter is
made up of molecules, and that in all bodies, at temperatures that we know, the
molecules are in constant motion. That is, all bodies that we know have heat . . .
[vol. 4, pp. 1617-1618]
Energy. Did you ever hear of a “perpetual motion machine?” . . . A perpetual
motion machine is a device which is supposed to run itself without fuel or other
outside aid, and yet is able to do work . . .
No such device has ever worked, although thousands of gifted mechanics have
wasted their lives trying to develop such machines. Further, science tells us that no
such machine ever will work. Why is this so? It is because nature seems to have
placed a certain amount of energy in the universe, and ruled that none of this
energy can ever be lost, nor can it be increased. We can merely transform
energy from one kind to another.
The railway locomotive shows how the principle works out. First the engine uses
coal, which is stored up energy, and turns it into heat energy by burning. The heat
energy turns the water in the boiler into steam, a form of expansive energy. The
engine turns this expansive energy into mechanical energy, which runs the engine.
From beginning to end, the chain is unbroken. We have transformed one kind of
energy into another; but at no time have we created any energy.
Neither, for that matter, have we lost energy. We didn’t get all the heat energy of
the coal in the form of steam. But the missing energy wasn’t destroyed. Some of it
warmed the air around the boiler; some went up the smokestack. It wasn’t destroyed;
it merely went where we didn’t want it. So too with the energy lost by friction in the
engine.
The statement that energy cannot be created or destroyed, but is merely transformed,
is called the law of conservation of energy . . .
What can the engineer do with energy? All the engineer can do is to devise
machines for transforming energy. He cannot make a machine to create energy.
And his greatest is to study nature’s sources of energy or stored-up work, so that he
can transform this into useful work. . . .
Now comes a remarkable fact, only recently discovered. If you were transforming
energy by heating iron until it gave off light, you might think that the more you
heated it, the more light it would give. This is not exactly true. Fine measurements
show that after it is glowing, the iron will absorb a certain amount of heat without
giving off more light; then just a trifle more heat will make it give off considerably
more light. It seems as though it has to absorb a definite quantity of energy
before it can change at all; then it changes all at once and emits the entire
amount absorbed.
Scientists have measured this mysterious “unity
quantity” of energy, called a quantum, and are
discovering why matter behaves this way. They think
that electrons do not absorb or give off energy while
merely moving in their orbits, but only when they
jump from one orbit to another, jumping to the outer
orbits when they absorb energy, and falling inward
when they emit energy. The “quantum” is the
amount needed to make one electron jump from one
orbit to the next, or given off when it falls inward one
orbit.
This wonderful story of the forces of nature and the
transformation and conservation of energy was
worked out about 1840 by Joule, Helmholtz, Kelvin,
and other men of the time. The quantum theory has
been added by Planck, Bohr, Einstein, and others, commencing about 1900. [vol. 3,
pp. 1148-1149]