A History of Science, vol 1 | Page 6

observation implied a necessary conception
of the complete revolution of these bodies about the earth. It is
unnecessary to speculate here as to how the primitive intelligence
conceived the transfer of the sun from the western to the eastern
horizon, to be effected each night, for we shall have occasion to
examine some historical speculations regarding this phenomenon. We
may assume, however, that the idea of the transfer of the heavenly
bodies beneath the earth (whatever the conception as to the form of that
body) must early have presented itself.
It required a relatively high development of the observing faculties, yet
a development which man must have attained ages before the historical
period, to note that the moon has a secondary motion, which leads it to
shift its relative position in the heavens, as regards the stars; that the
stars themselves, on the other hand, keep a fixed relation as regards one
another, with the notable exception of two or three of the most brilliant
members of the galaxy, the latter being the bodies which came to be
known finally as planets, or wandering stars. The wandering
propensities of such brilliant bodies as Jupiter and Venus cannot well
have escaped detection. We may safely assume, however, that these
anomalous motions of the moon and planets found no explanation that
could be called scientific until a relatively late period.
3. Turning from the heavens to the earth, and ignoring such primitive
observations as that of the distinction between land and water, we may
note that there was one great scientific law which must have forced
itself upon the attention of primitive man. This is the law of universal
terrestrial gravitation. The word gravitation suggests the name of
Newton, and it may excite surprise to hear a knowledge of gravitation
ascribed to men who preceded that philosopher by, say, twenty-five or
fifty thousand years. Yet the slightest consideration of the facts will
make it clear that the great central law that all heavy bodies fall directly
towards the earth, cannot have escaped the attention of the most
primitive intelligence. The arboreal habits of our primitive ancestors
gave opportunities for constant observation of the practicalities of this
law. And, so soon as man had developed the mental capacity to
formulate ideas, one of the earliest ideas must have been the conception,

however vaguely phrased in words, that all unsupported bodies fall
towards the earth. The same phenomenon being observed to operate on
water-surfaces, and no alteration being observed in its operation in
different portions of man's habitat, the most primitive wanderer must
have come to have full faith in the universal action of the observed law
of gravitation. Indeed, it is inconceivable that he can have imagined a
place on the earth where this law does not operate. On the other hand,
of course, he never grasped the conception of the operation of this law
beyond the close proximity of the earth. To extend the reach of
gravitation out to the moon and to the stars, including within its
compass every particle of matter in the universe, was the work of
Newton, as we shall see in due course. Meantime we shall better
understand that work if we recall that the mere local fact of terrestrial
gravitation has been the familiar knowledge of all generations of men.
It may further help to connect us in sympathy with our primeval
ancestor if we recall that in the attempt to explain this fact of terrestrial
gravitation Newton made no advance, and we of to-day are scarcely
more enlightened than the man of the Stone Age. Like the man of the
Stone Age, we know that an arrow shot into the sky falls back to the
earth. We can calculate, as he could not do, the arc it will describe and
the exact speed of its fall; but as to why it returns to earth at all, the
greatest philosopher of to-day is almost as much in the dark as was the
first primitive bowman that ever made the experiment.
Other physical facts going to make up an elementary science of
mechanics, that were demonstratively known to prehistoric man, were
such as these: the rigidity of solids and the mobility of liquids; the fact
that changes of temperature transform solids to liquids and vice
versa--that heat, for example, melts copper and even iron, and that cold
congeals water; and the fact that friction, as illustrated in the rubbing
together of two sticks, may produce heat enough to cause a fire. The
rationale of this last experiment did not receive an explanation until
about the beginning of the nineteenth century of our own era. But the
experimental fact was so well known to prehistoric man that he
employed this method, as various savage tribes employ it to this