respecting the Pkcenomena of Eledricify. 103 



iricjiidd of the halls, they are certainly negative comparatively 

 to the ground and the amlievt air ; but the deferent Jiuid of the 

 positive disks giving more expansive power to their electric 

 matter, a conductor communicating with the ground may be 

 brought into immediate contact with them without effect : their 

 negative divergence still continues. The same phsenomenon is 

 produced by inversely electrifying the horizontal insulated con- 

 ductor and the disks : when the balls, Xhew positive, are made to 

 communicate with the ground by a brass conductor, they con- 

 tinue to diverge, being under the infuence of the negative at- 

 viospliere of the disks. 



26. These phaenomena much interested M. Cavallo, who was 

 a very liberal-minded man. He persisted in his opinions as 

 long as he found reasons to defend them, but was ready to aban- 

 don them whenever his arguments appeared to be contradicted 

 by facts, to which he was very attentive. Having made some 

 stay at Windsor, he came often to me and proposed some altera- 

 tions in -my apparatus, which he thought could change the phee- 

 iiomena. I foretold him what would happen by tiie changes, 

 some of which would change the effect on account of causes 

 which I pointed out, and others would produce the same effect. 

 At last he saw and acknowledged that those phaenomeaa could 

 absolutely not be explained but Iiy admitting the composition of 

 the electric Jiuid of two ingredients, one of which only, which I 

 had called electric matter, produced electric motions^ and the 

 other, which gave expansibility to that matter in proportion to 

 its relative quantity, which I named electric deferent. Thus 

 Volta's theory, applied to all the electric phsenomeiia which were 

 opposed to Franklin's theory, in his own expressions, have cleared 

 the system oi positive and negative electricities from the objec- 

 tions of Mr. Donovan, arising from the erroneous principle which 

 he admitted in it, of a natural cjuuntity of electric ^natter be- 

 longing to all terrestrial bodies. 



27. I come to another \erv important object in the science 

 of electricity, that of the effect of friction, which in vol. xxxiii. 

 of Mr. Nicliolson's Philosophical Journal I have explained in a 

 manner different from that of Mr. Donovan in p. 337. His 

 hypothesis is this : " That during attrition between bodies, one 

 of which must be an electric, the pores of the latter being open 

 will receive the plus quantity, and will give it out again when 

 the pores close," — In this respect I have proved, that there is no 

 other distinction between bodies than that of conductors and 7ion- 

 eonduetors ; the latter of which only can be excited hy friction y 

 because the electric fluid, thus set in motion on the surface, 

 moves slowly to inake its escaj)e by a conductor offered at a di- 



G 4 stance. 



