Aristotle off by heart, and any disposition to doubt or even to
question the doctrines of the venerated teacher was regarded as
intolerable presumption. But young Galileo had the audacity to think
for himself about the laws of nature. He would not take any
assertion of fact on the authority of Aristotle when he had the means
of questioning nature directly as to its truth or falsehood. His
teachers thus came to regard him as a somewhat misguided youth,
though they could not but respect the unflagging industry with which
he amassed all the knowledge he could acquire.

[PLATE: GALILEO'S PENDULUM.]

We are so accustomed to the use of pendulums in our clocks that
perhaps we do not often realise that the introduction of this method
of regulating time-pieces was really a notable invention worthy the
fame of the great astronomer to whom it was due. It appears that
sitting one day in the Cathedral of Pisa, Galileo's attention became
concentrated on the swinging of a chandelier which hung from the
ceiling. It struck him as a significant point, that whether the arc
through which the pendulum oscillated was a long one or a short one,
the time occupied in each vibration was sensibly the same. This
suggested to the thoughtful observer that a pendulum would afford the
means by which a time-keeper might be controlled, and accordingly
Galileo constructed for the first time a clock on this principle. The
immediate object sought in this apparatus was to provide a means of
aiding physicians in counting the pulses of their patients.

The talents of Galileo having at length extorted due recognition from
the authorities, he was appointed, at the age of twenty-five,
Professor of Mathematics at the University of Pisa. Then came the