respecting the Phmnotnena of Electricity. 99 



munication with the ground. The machine being worked in 

 this state, a luminous point was seen at the extremity of the 

 point fixed to the rubber, indicating that some electric fluid 

 passed from the air of the room to the ruhl'er, and thus tliat air 

 was made negative. Now the pair of balls, which did not 

 again diverge in the next room, being brought into that wherein 

 the machine was, they strongly dii'erged, and by the test they 

 diverged positively, being l)rought into an atmosphere rendered 

 negative l)v the point fixed to the rubier, 



11. These experiments cannot leave any doubt, on Volta's 

 theory, that in the divergence of a pair of balls, the standard of 

 plm and minus is not^ as Franklin had determined it, a natural 

 electric state of bodies ; but that it is the actual and variable 

 electric state of the ambient air. Had Mr. Donovan been ac- 

 (juainted with that theory of Volta, still retaining the fundamental 

 theory oi positive und vegatii'e, first announced by Franklin, but 

 changing the standard from a Jixed to a changeable state v/ell 

 defined, he would certainly have retained the fundamental doc- 

 trine of positive and negatiue with that correction, 



12. As to the theory of .^pinus, that electric atmospheres do 

 vot exist, which Mr. Donovan seems to prefer to that of Franklin 

 corrected by Volta, — I have shown in one of my works, that 

 iEpinus, instead of simplifying the theory, has fallen into a greater 

 complication of hypotheses, even contrary to some general laws 

 of nature. But I* shall not enter into that discussion, as Volta's 

 system renders it unnecessary. 



13. It is by this influence of the air, receiving its share of the 

 electric fluid possessed bv the bodies u-hich it surrounds, that 

 Voha explained the motions of electrified balls, and the following 

 is liis explanatidii. " When two balls suspended near each other 

 are in a positive state compar?.tively to the air of the place, they 

 loth communicate some electric fluid to the air between them; 

 while each of them communicates alone the electric fluid to the 

 outward air. Each of the balls therefore moves towards that 

 outward air on each side, not by repelling each other, but by 

 moving towards the air possessing less electric fluid. 



14. During the course of my experiments to demonstrate, in 

 various manners, the certainty of Volta's system on the cause of 

 motion of electrified balls, it came into my mind that an analogous 

 phtenomenon might be produced, in which the came of the mo- 

 tion might be visible ; and it havin}> succeeded, I have described 

 this experiment from p. 116 to 119 of the same volume, of 

 which it will be sufficient to give here an extract, 



15. An accidental observation led me to that experiment, 

 which those who shave themselves and employ soap powder will 

 cu-ily repeat. If the basin used happens to be covered with 



G 2 dust J 



