2/4 Memoir upon the compound 



proximity to the earth, or by some other means ; and let this 

 cloud, containing thennogen, be carried by the wind under an- 

 other cloud (B) in its natural state, then this cloud will become 

 electrified by induction ; for the therniogen which it contains 

 will be expelled from it into the air above ; and when the cloud 

 A is carried away by the wind, the cloud B will remain electri- 

 fied, and in a state contrary to that of A, like the brass ball in 

 the second experiment. 



The air above the cloud B having received an additional 

 charge of thermogeu, and this element having a strong attrac- 

 tion for moisture*, will attract moistin-e from the surrounding 

 air, and thus a new cloud will be formed. 



When the cloud A is carried away from under the cloud B, 

 let it be supposed that it jiasses over or under a very thin cloud, 

 then will this cloud be electrified by induction ; but it will receive 

 the same element as that of the cloud A : the reason of which is 

 shown by the second experiment. 



As an excited barometer tube will produce an electrical effect 

 at the distance of four or five feet, it may be supposed that a 

 cloud iiighly electrified may affect other clouds at the distance 

 of some miles. And hence we may infer that all those various 

 changes, which are daily taking place among the clouds, may 

 arise from that unerring law of nature called inducted electri- 

 city f. 



Lynn, Oct. 10, 1814. Ez. WalkER. 



[To be continued.] 



XLIV. Memoir 7tpon the compound and smooth or simple Eyes 

 of Insects, and on the Manner in which these two Species of 

 Eyes concur in Vision. By M. IMarcel de Serres, Pro- 

 fessor oj the Sciences in the Imperial University. 



[Continued from page 191.] 



III. On the Mechanism of Vision. 



JL HE eyes of insects, according to the foregoing observations, arfe 

 formed in a very difl'erent manner from those of the vertebral 

 animals, or even the molluscae, am.ong which there also exist 

 distinct humours. Nothing similar is seen in the eyes of insects 

 which, deprived of every humour, appear as it were to feel 

 the light almost immediately. Although formed in a manner 

 so peculiar, these organs are nevertheless eyes, as we may be 



* Phil. Mag, vol. xliii. p. 252. 



t Dr. Franklin discovered tliat tlie clouds would cbnnge from positive 

 to negative electricity, several times in the course of one tljunder-gust. 



convinced 



