264 POPULAR SCIENCE MONTHLY. 



with argument. Galileo's retorts were bitter and brilliant, his sar- 

 casms 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 through- 

 out 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 recom- 

 mended him to his friends in Venice, and as a result he was appointed 

 to be professor of mathematics at the University of Paclua, for a term 

 of six years, this time at a salary of 72 zecchini, about $90. He re- 

 mained 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, fortifica- 

 tion, mechanics and the like. His lectures were thronged with stu- 

 dents. 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 e Floren- 

 tine ' 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 win- 

 ter cold to 20°. So late as 1741 Florentine thermometers were in com- 

 mon 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, Beaumer's from 1730, Celsius's (the 

 centigrade) from 1742-3. 



