tronomy that fought the battle of, and won the victory for, the new
principles of research. Its glory was not so much its positive
addition to knowledge, great as that was, but its mode of thought. By
pure reason a new system was established and triumphed over the
testimony of the senses and of all {638} previous authority, even that
which purported to be revelation. Man was reduced to a creature of
law; God was defined as an expression of law.

How much was man's imagination touched, how was his whole thought and
purpose changed by the Copernican discovery! No longer lord of a
little, bounded world, man crept as a parasite on a grain of dust
spinning eternally through endless space. And with the humiliation
came a great exaltation. For this tiny creature could now seal the
stars and bind the Pleiades and sound each deep abyss that held a sun.
What new sublimity of thought, what greatness of soul was not his! To
Copernicus belongs properly the praise lavished by Lucretius on
Epicurus, of having burst the flaming bounds of the world and of having
made man equal to heaven. The history of the past, the religion of the
present, the science of the future--all ideas were transmuted, all
values reversed by this new and wonderful hypothesis.

But all this, of course, was but dimly sensed by the contemporaries of
Copernicus. What they really felt was the new compulsion of natural
law and the necessity of causation. Leonardo was led thus far by his
study of mathematics, which he regarded as the key to natural science.
He even went so far as to define time as a sort of non-geometrical
space.

[Sidenote: Theory of knowledge]

Two things were necessary to a philosophy in harmony with the
scientific view; the first was a new theory of knowledge, the second
was a new conception of the ultimate reality in the universe.
Paracelsus contributed to the first in the direction of modern
empiricism, by defending understanding as that which comprehended
exactly the thing that the hand touched and the eyes saw. Several
immature attempts were made at scientific skepticism. That of
Cornelius Agrippa--_De incertitudine et vanitate scientiarum et {639}
artium atque excellentia Verbi Dei declamatio_--can hardly be taken
seriously, as it was regarded by the author himself rather as a clever
paradox. Francis Sanchez, on the other hand, formulated a tenable
theory of the impossibility of knowing anything. A riper theory of
perception