cillations of the sun. We shall see that, even at a relatively late
period, the vaguest notions were still in vogue as to the cause of the
sun's changes of position.

That the sun, moon, and stars move across the heavens must obviously
have been among the earliest scientific observations. It must not be
inferred, however, that this 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