1632, he was careful to confine his researches, or at least his
publications, to topics that seemed free from theological
implications. In doing so he reverted to the field of his
earliest studies --namely, the field of mechanics; and the
Dialoghi delle Nuove Scienze, which he finished in 1636, and
which was printed two years later, attained a celebrity no less
than that of the heretical dialogue that had preceded it. The
later work was free from all apparent heresies, yet perhaps it
did more towards the establishment of the Copernican doctrine,
through the teaching of correct mechanical principles, than the
other work had accomplished by a more direct method.

Galileo's astronomical discoveries were, as we have seen, in a
sense accidental; at least, they received their inception through
the inventive genius of another. His mechanical discoveries, on
the other hand, were the natural output of his own creative
genius. At the very beginning of his career, while yet a very
young man, though a professor of mathematics at Pisa, he had
begun that onslaught upon the old Aristotelian ideas which he was
to continue throughout his life. At the famous leaning tower in
Pisa, the young iconoclast performed, in the year 1590, one of
the most theatrical demonstrations in the history of science.
Assembling a multitude of champions of the old ideas, he proposed
to demonstrate the falsity of the Aristotelian doctrine that the
velocity of falling bodies is proportionate to their weight.
There is perhaps no fact more strongly illustrative of the temper
of the Middle Ages than the fact that this doctrine, as taught by
the Aristotelian philosopher, should so long have gone
unchallenged. Now, however, it was put to the test; Galileo
released a half-pound weight and a hundred-pound cannon-ball from