proposed to pump out a dock. But Galileo showed up the absurdity of
this enterprise in such an aggressive manner that Don Giovanni took
mortal offence, nor was he mollified when the truths of Galileo's
criticisms were abundantly verified by the total failure of his
ridiculous invention. In various ways Galileo was made to feel his
position at Pisa so unpleasant that he was at length compelled to
abandon his chair in the University. The active exertions of his
friends, of whom Galileo was so fortunate as to have had throughout
his life an abundant supply, then secured his election to the
Professorship of Mathematics at Padua, whither he went in 1592.

[PLATE: PORTRAIT OF GALILEO.]

It was in this new position that Galileo entered on that marvellous
career of investigation which was destined to revolutionize science.
The zeal with which he discharged his professorial duties was indeed
of the most unremitting character. He speedily drew such crowds to
listen to his discourses on Natural Philosophy that his lecture-room
was filled to overflowing. He also received many private pupils in
his house for special instruction. Every moment that could be spared
from these labours was devoted to his private study and to his
incessant experiments.

Like many another philosopher who has greatly extended our knowledge
of nature, Galileo had a remarkable aptitude for the invention of
instruments designed for philosophical research. To facilitate his
practical work, we find that in 1599 he had engaged a skilled workman
who was to live in his house, and thus be constantly at hand to try
the devices for ever springing from Galileo's fertile brain. Among
the earliest of his inventions appears to have been the thermometer,