^&, • I'HILOSOPHICAL TRANSACTIONS. [aNNO J778. 



at the same time ; viz. towards the electrified body it acquires a contrary elec- 

 tricity, and at the opposite extremity it acquires the same kind of electricity 

 with the electrified body. 



It seems therefore to be a law of nature, that the electric fluid which is accu- 

 mulated on a body, and finds an obstruction in its free passage to another neigh- 

 bouring body by the interposition of a non-conducting body (such as dry air, 

 glass, &c.) forces, by its repulsive power, the electric fluid, naturally contained 

 in all bodies, to the farthest extremity of the neighbouring body, so as to excite 

 in its nearest extremity a kind of defect of the electric fluid, or a kind of vacuum, 

 till at last the accumulation of the electric fluid becomes so great on the electri- 

 fied body, that it overpowers the resistance of the intermediate non-conducting 

 substance, forces its way through it, and rushes in the form of a spark on the 

 neighbouring body. 



If the electric fluid be thrown on the surface of a pane of glass, coated on 

 both sides with a metallic substance, such as tin foil ; the fluid, finding an ob- 

 struction to its passage through the body, is crowded on that surfitce of the 

 glass which has received it ; forces the electric fluid out of the other surface, if 

 some conducting body is near it, or in contact with it, and can convey it away; 

 till this fluid becomes so much crowded on that surface as to overpower the re- 

 sistance of the glass, and to force its way through the substance of the glass, in 

 order to diffuse itself on the other surface, on which was produced a kind of 

 vacuum. The glass, being thus rent, is no longer able to be what is called 

 charged ; but after the crowded electrical fluid of a prime conductor has in the 

 same manner rent the plate of air (which obstructed to a certain degree its free 

 passage between the prime conductor and the neighboui ing body) by giving it a 

 spark, the same spark may be repeated at pleasure, because the opening formed 

 by the spark through the plate of air is immediately shut up again according to 

 the nature of all fluids. 



If an insulated conducting body be situated in the manner described, so as to 

 possess at its different extremities a contrary electricity, it ma) inipart to any 

 other body brought in contact with it, or within its striking distance, a share of 

 that electricity which it has acquired at its farther extremity. The former body, 

 so touched, has effectually lost that part of electrical fluid which was in a certain 

 manner crowded on that extremity ; and therefore, being taken out of the 

 sphere of action of the excited body, as, for instance, a prime conductor, after 

 having thus lost a part of the electric fluid crowded on its extremity, is found to 

 possess a negative electricity if the excited body had a positive, and a positive if 

 the excited body had a negative one. 



Thus we see how far we must believe what is commonly affirmed as a fact, that 

 a body, plunged in the atmosphere of an electrified body, acquires a state of 



