respecling the "Phcenomena of Electricity . 101 



but the surface of which is of a certain extent ; the particles of 

 air in motion, returning from the electrified conductor, and 

 tlnis possessing more electric fluid, might transmit some to the 

 other body ; but their influence on it producing a diminution of 

 tension in the fluid proceeding from the conductor, at the same 

 time that they increase the tension in the fluid of the body, 

 there is thus a very small disposition of the electric fluid to 

 abandon the particles of air. But if it be a point, the electric 

 fluid belonging to it is in too small a quantity to increase the 

 tension of that belonging to the body: thus, every particle of air 

 which comes in contact with that body discharges its electric 

 fluid, returns instantly, and, as it takes the shorter way, thus is 

 produced a current of air. The same alternate motions take place 

 in the particles of air, whether the point is negative or positive. 



20. The difliculty concerning the impermealility of glass 

 to the electric fluid, which the autlior opposes to the pha^no- 

 mena of the Leyden vial, as accounted for by Franklin, has also 

 been removed by Volta, by supposing the electric fluid composed 

 of two ingredients, to one of which only glass is impermealdey 

 but the other passes readily through it. If the jar is coated on 

 l^oth sides with tin-foil up to a certain height, it will not receive 

 a charge, unless the outside coating is in commuiiication with 

 the ground. 



21. On the explanation of this common phenomenon rests 

 the whole theory of p05i/i/;e and negative electricities, which Volta, 

 having placed on its true foundation, has thereby clearly explained 

 the pliaenomena of the Leyden vial ; and it is his theory which has 

 led me to my systems on the nature of the electric fltiid. This 

 fluid, considered in its common phenomena, is composed of two 

 ingredients; one, which does not possess expansibilityby itself; the 

 other, which, united with it, gives expansibility to the compound. 

 Of this union I have given an example in the nqiieoiis vapouVy 

 which is composedof particles of i^'rt/er, asub-itance not possess- 

 ing expansibility, and of particles oi fire, which gives expansibihty 

 to the compound. — That analogy, with all its particulars, I have 

 explained in p. 77, sf'ction I. with this title :" Analogies and 

 Differences of the Electric Fluid, and the Aqueous Vapour." In 

 consccjuence of this analogy, I have given the name of electric 

 matter to that ingredient of the electric fluid to which glass is 

 not permeable, and deferent fluid to that ingredient Avhich trans- 

 ports the electric matter, and which alone passes through the 

 glass. 



22. In this system Mr. Donovan may find the solution of his 

 difficulties concerning the charge and discharge of the Leyden 

 vial. Franklin's system is true so fur as he supposes that the 



G 3 vial 



