148 A Short History of Astronomy [CH. vi. 



weight ; but if so he would probably have said that it would 

 fall ten times as far, or else that it would require ten times 

 as long to fall the same distance. To actually try the 

 experiment, to vary its conditions, so as to remove as many 

 accidental causes of error as possible, to increase in some 

 way the time of the fall so as to enable it to be measured 

 with more accuracy, these ideas, put into practice by Galilei, 

 were entirely foreign to the prevailing habits of scientific 

 thought, and were indeed regarded by most of his col- 

 leagues as undesirable if not dangerous innovations. A 

 few simple experiments were enough to prove the complete 

 falsity of the current beliefs in this matter, and to establish 

 that in general bodies of different weights fell nearly the 

 same distance in the same time, the difference being not 

 more than co Id reasonably be ascribed to the resistance 

 offered by the air. 



These and other results were embodied in a tract, which, 

 like most of Galilei's earlier writings, was only circulated 

 in manuscript, the substance of it being first printed in the 

 great treatise on mechanics which he published towards 

 the end of his life ( 133). 



These innovations, coupled with the slight respect that 

 he was in the habit of paying to those who differed from 

 him, evidently made Galilei far from popular with his 

 colleagues at Pisa, and either on this account, or on account 

 of domestic troubles consequent on the death of his father 

 (1591), he resigned his professorship shortly before the 

 expiration of his term of office, and returned to his mother's 

 home at Florence. 



117. After a few months spent at Florence he was 

 appointed, by the influence of a Venetian friend, to a 

 professorship of mathematics at Padua, which was then in 

 the territory of the Venetian republic (1592). The ap- 

 pointment was in the first instance for a period of six years, 

 and the salary much larger than at Pisa. During the first 

 few years of Galilei's career at Padua his activity seems 

 o have been very great and very varied ; in addition to 

 jiving his regular lectures, to audiences which rapidly in- 

 creased, he wrote tracts, for the most part not printed at 

 the time, on astronomy, on mechanics, and on fortification, 

 and invented a variety of scientific instruments. 



