i 7 6 



HISTORY OF SCIENCE. 



which it rests, has been claimed for several different persons. Some 

 find evidence that the idea originally occurred to Hero, the Greek 

 mathematician ; others claim it for Galileo ; but the names of SAN- 

 TORIO and of DREBBEL are most commonly associated with the inven- 

 tion. In the form of the air-thermometer it is a simple arrangement 

 which might easily present itself independently to the experimenters of 

 the seventeenth century. In a letter written in 1638, Castelli stated 



