456 THE) INTELLECTUAL RISE IN ELECTRICITY. 



efforts; so that, after having invented one of the most in- 

 genious and natural theories imaginable, she will have the 

 perversity to act directly in the teeth of his system, and 

 flatly contradict his most favorite positions." 1 



Bernouilli gave not only an elaborate explanation of 

 the effect in accordance with the Cartesian theory, by as- 

 suming different matters respectively entering the vacuum 

 through the glass from without and arising from the mer- 

 cury within and then clashing together (in which he was 

 quite safe, seeing that he was comimmicating with the 

 Cartesian stronghold); but also laid down numerous pre- 

 cautions, which he said it was indispensable to observe in 

 order to reproduce the effect. This last rather surprised 

 the Frenchmen, because Cassini for one had been getting 

 light from his barometer for the last six years without 

 troubling himself with any precautions at all. And 

 Picard's old instrument had been taken to pieces by De la 

 Hire and set up over again, and sometimes it had given 

 light and sometimes refused to do it, from apparent sheer 

 wilfulness. In fact Cassini and De la Hire had compared 

 notes, and even thought they found differences in the sort 

 of light which their respective barometers yielded. How- 

 ever, it was thought best to follow Bernouilli' s directions, 

 with the unexpected sequel that the apparatus so made 

 refused to glow at all while more people began to pro- 

 duce instruments which behaved beautifully. 



Bernouilli, on being informed, calmly modified his 

 requirements, insisting, however, upon absolutely pure 

 mercury and total exclusion of air. But old barometers 

 obviously containing air bubbles still persisted in glowing. 

 Then Bernouilli himself discovered that the vacuum was 

 not needed, and that mercury shaken in an ordinary vial 

 shone finely. The French Academy seems to have been 

 unable to reproduce this, and Bernouilli investigated the 

 matter far enough to reach firm ground. He found that 

 so long as the mercury was fairly pure he could get lumi- 



1 Irving: Knickerbocker History of New York. 



