shouting, echo the voices to the stars of heaven, and horsemen fly
about, and suddenly wheeling, scour across the middle of the plains,
shaking them with the vehemence of their charge. And yet there is some
spot on the high hills, seen from which they appear to stand still and
to rest on the plains as a bright spot."

The atomic theory of the Greek thinkers was constructed by reasoning
on natural phenomena. Lucretius constantly appeals to observed facts
for confirmation of his theoretical teachings, or refutation of
opinions he thought erroneous. Besides giving a general mental
presentation of the material universe, the theory was applied to many
specific transmutations; but minute descriptions of what are now
called chemical changes could not be given in terms of the theory,
because no searching examination of so much as one such change had
been made, nor, I think, one may say, could be made under the
conditions of Greek life. More than two thousand years passed before
investigators began to make accurate measurements of the quantities of
the substances which take part in those changes wherein certain
things seem to be destroyed and other totally different things to be
produced; until accurate knowledge had been obtained of the quantities
of the definite substances which interact in the transformations of
matter, the atomic theory could not do more than draw the outlines of
a picture of material changes.

A scientific theory has been described as "the likening of our
imaginings to what we actually observe." So long as we observe only in
the rough, only in a broad and general way, our imaginings must also
be rough, broad, and general. It was the great glory of the Greek
thinkers about natural events that their observations were accurate,
on the whole, and as far as they went, and the theory they formed was