211 OF ELECTRICITY. CHAP. 7- 2. 



SECTION II. 



Of the Electricity of Thunderclouds ; and of 

 Lightning. 



IT has appeared by some experiments, that a 

 Thundercloud exercises its electrical influence 

 on the surrounding air, and throws it into an 

 opposite state : so that if the cloud be positively 

 electrified, there will be a portion of air nega- 

 tively electrified around it ; and, beyond that, 

 a positively electrified portion perhaps again. 

 But a sufficient number of experiments have 

 not as yet been made with electrometers, to 

 certify whether this be the case with all clouds. 

 It is probable that most of the flashes of 

 Lightning never reach the ground, but are 

 only communications between the Thunder- 

 cloud and some other either oppositely or not 

 at all electrified. 



The hypothesis of Van Mons, that the two 

 different kinds of Thunder and Lightning are 

 the result of very dissimilar causes, that one is 

 the combustion of the gases of water, and the 

 other the discharge of the electric spark, seems 

 wanting in positive proof. Their reports are 



