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