332 A Reply to Mr. Donovan's Ohsurvations. 



ments witli an excited glass tube, which he brought under a 

 pith-ball, anrl when removing the tu//e, the ball remained posi- 

 tive. This effect was probably owing to the aqueons vapour 

 being then abundant in the room, and thus producing a con- 

 duct big medium. 



Coming now to the great object of electricity, namely, the di- 

 vergence oi i\\e electrified bull, which is our electrometer ; Mr.D. 

 declares with ingenuousness that he has not had ojjportunity to see 

 Volta's system completely stated ; but he says, if I understand, 

 it relates to two bodies, one of which is in a natural state, and 

 the other in a super-natural state. But this is a misconception : 

 Volta's theory relates to two bodies, huth either positive or nega^ 

 tive; and this diver ^ence I have thus explained from Volta's 

 theory, as- in a pair of bails thus situated, hotk act to bring the 

 air bttioecn tliem to their electric slate ; while one only acts on 

 the external air on both sides, to which therefore they tend de- 

 cidedly. 



Mr. Donovan objects against that explanation, " that it vir- 

 tually destroys the principle of repulsion, and refers all to attrac- 

 tion" This is true in the common acceptation of the words at- 

 trnclio7i and repuhion ; but in ftrict natural philosophy, they 

 ought to be called tendencies, as a vi-ible effect, not implying the 

 idea of cause, of which we might remain ignorant. But Mr. 

 Donovan asks, " How can it be supposed at the same time, that 

 electricity is an elastic fluid P" In Volta's theory electricity is 

 only considered as an elastic fluid, in the upper region of the 

 atujosphere ; for, when it is produced in a manner which I have 

 explained, it darts in a straight line and soon vanishes, as seen in 

 lightninir. But within the atmosphere it is a parasite fluid, al- 

 ways fixed to the particles of air; and I have proved, bv an ex- 

 periment related in my work Idees sur la Meteomlogic, that a 

 perfect vacuum free from aqueous vapoztr is not a conductor. 

 This experiment 1 made in presence of Dr. Franklin and some 

 other experimental philosophers, who, knowing my opinion, de- 

 sired to submit it to a test which Dr. Franklin himself prescribed. 

 I performed the experiment, by which it was completely proved 

 that a perfect vacmim did not transmit the electric fluid. Thus, 

 after having doubted, they were fully convinced of this fact, that 

 the electric fluidh really a parasite fluid, always attached to the 

 particles of some atmospheric fluid and moving with them. 



There remains another object of disagreement between Mr. 

 Donovan and myself^ concerning the impermeability of glass to 

 the electric matter, which in my works on Electricity I had 

 uiaintained as the real cause of the phajnomena of the Leyden 

 vial. On this object Mr. Donovan refers me to an interesting 

 experiment which he has made, and thus describes: "A thin 



fla.sk 



