Page:Popular Science Monthly Volume 66.djvu/268

264 with argument. Galileo's retorts were bitter and brilliant, his sarcasms searching and unsparing. Before the end of his three years' engagement as professor had expired, he had involved himself in a hopeless wrangle with his colleagues and with Aristotelians throughout Italy. An imbroglio with John of Medici put him out of favor at court also at this very time. The nephew of the reigning Duke of Florence had invented a machine for dredging the harbor of Leghorn, and the plans were submitted to Galileo, who declared the apparatus to be useless, as indeed it was. He made no friends by this candor and gave another weapon to his enemies which they were not slow to use. The students in the university were incited against him and he was publicly hissed at lectures, so that he felt it advisable to resign his professorship (1591).

He returned to Florence discredited and out of favor. His father died in July of this year, leaving his family in distress for money. Galileo's friend and patron, the Marquis del Monte, warmly recommended him to his friends in Venice, and as a result he was appointed to be professor of mathematics at the University of Padua, for a term of six years, this time at a salary of 72 zecchini, about $90. He remained titular professor for a period of eighteen years, until 1610, his appointment being three times renewed and his emoluments increased to $500. In December, 1592, he entered upon his duties. His lessons embraced a wide range of subjects: astronomy, gnomonics, fortification, mechanics and the like. His lectures were thronged with students. The halls were not spacious enough to hold them all and at times he taught in the open air.

In 1597 he invented his proportional compasses of which he was very proud. His manuscript description of them was plagiarized by one Balthasar Capra, and Galileo's scathing review of the work excited general notice for its bitter satire. He was already recognized as an adversary to be feared.

It has lately been demonstrated that we owe the invention of the thermometer to Galileo. His first instrument appears to have been a crude air thermometer devised in 1595. It was soon (1611) applied by physicians to the diagnosis of fevers and about 1641 to regular meteorological observations of temperature. The scales were arbitrary. The idea was developed by his pupils in various ways. The ‘Florentine’ thermometers used by the Accademia del Cimento (1657-1667) had straight sealed tubes connected with bulbs filled with spirits of wine. The highest summer heat corresponded to 80°, the lowest winter cold to 20°. So late as 1741 Florentine thermometers were in common use throughout Europe. It was not till 1694 that the freezing and boiling points of water were proposed as standard. Fahrenheit's thermometer date from 1709, Réaumer's from 1730, Celsius's (the centigrade) from 1742-3.