. Throughout this period there
is scarcely a generation that has not produced great scientific
thinkers--men who have put their mark upon the progress of civilization;
but we shall see, as we look forward for a corresponding period, that
the ensuing thirty generations produced scarcely a single scientific
thinker of the first rank. Eight hundred years of intellectual
activity--thirty generations of greatness; then eight hundred years of
stasis--thirty generations of mediocrity; such seems to be the record
as viewed in perspective. Doubtless it seemed far different to the
contemporary observer; it is only in reasonable perspective that any
scene can be viewed fairly. But for us, looking back without prejudice
across the stage of years, it seems indisputable that a great epoch came
to a close at about the time when the barbarian nations of Europe began
to sweep down into Greece and Italy. We are forced to feel that we have
reached the limits of progress of what historians are pleased to call
the ancient world. For about eight hundred years Greek thought has been
dominant, but in the ensuing period it is to play a quite subordinate
part, except in so far as it influences the thought of an alien race. As
we leave this classical epoch, then, we may well recapitulate in brief
its triumphs. A few words will suffice to summarize a story the details
of which have made up our recent chapters.

In the field of cosmology, Greek genius has demonstrated that the earth
is spheroidal, that the moon is earthlike in structure and much smaller
than our globe, and that the sun is vastly larger and many times more
distant than the moon. The actual size of the earth and the angle of its
axis with the ecliptic have been measured with approximate accuracy.
It has been shown that the sun and moon present inequalities of motion
which may be theoretically explained by supposing that the earth is not
situated precisely at the centre of their orbits. A system of eccentrics
and epicycles has been elaborated which serves to explain the apparent
motions of the heavenly bodies in a manner that may be called scientific
even though it is based, as we now know, upon a false hypothesis. The
true hypothesis, which places the sun at the centre of the planetary
system and postulates the orbital and axial motions of our earth in
explanation of the motions of the heavenly bodies, has been put forward
and ardently championed, but, unfortunately, is not accepted b