time when he felt himself strong enough to throw down the gauntlet to
the adherents of the old philosophy. As a necessary part of his
doctrine on the movement of bodies Aristotle had asserted that the
time occupied by a stone in falling depends upon its weight, so that
the heavier the stone the less time would it require to fall from a
certain height to the earth. It might have been thought that a
statement so easily confuted by the simplest experiments could never
have maintained its position in any accepted scheme of philosophy.
But Aristotle had said it, and to anyone who ventured to express a
doubt the ready sneer was forthcoming, "Do you think yourself a
cleverer man than Aristotle?" Galileo determined to demonstrate in
the most emphatic manner the absurdity of a doctrine which had for
centuries received the sanction of the learned. The summit of the
Leaning Tower of Pisa offered a highly dramatic site for the great
experiment. The youthful professor let fall from the overhanging top
a large heavy body and a small light body simultaneously. According
to Aristotle the large body ought to have reached the ground much
sooner than the small one, but such was found not to be the case. In
the sight of a large concourse of people the simple fact was
demonstrated that the two bodies fell side by side, and reached the
ground at the same time. Thus the first great step was taken in the
overthrow of that preposterous system of unquestioning adhesion to
dogma, which had impeded the development of the knowledge of nature
for nearly two thousand years.

This revolutionary attitude towards the ancient beliefs was not
calculated to render Galileo's relations with the University
authorities harmonious. He had also the misfortune to make enemies
in other quarters. Don Giovanni de Medici, who was then the Governor
of the Port of Leghorn, had designed some contrivance by which he