ELECTRICITY. 



63 



air is withdrawn. It is a confirmation 

 of this hypothesis, respecting the pecu- 

 liar kind of obstruction which air op- 

 poses to the passage of electricity, that 

 other substances have been discovered 

 in which a similar property exists. Mr. 

 Ermann, of Berlin, has found that the 

 flame of alcohol is possessed of a greater 

 conduct ilia; power with regard to posi- 

 tive, than to negative electricity. Alka- 

 line soap, on the contrary, conducts ne- 

 gative electricity better than positive ; 

 and will, therefore, serve to insulate a 

 IV degree of the latter, at the same 

 ti> hat it permits the passage of the 



:.) It has always been urged as a 

 objection to the theory of a single 



c fluid, that it necessarily involves 

 * Condition of a mutual "repulsion 

 K ^ng the particles of ordinary matter. 

 8ee$ 52. Before attempting to combat 

 this objection, it will be proper to enter 

 into a somewhat fuller illustration of the 

 position than we have already done ; 

 and for this purpose we shall avail our- 

 selves of the assistance of a few dia- 

 grams, calculated to aid our conceptions 

 of the forces concerned in the mutual 

 Actions of electrified or neutral bodies. 

 For the sake of greater distinctness, we 

 shall suppose the whole of the matter 

 in the body, of which we are studying 

 the actions, to be concentrated in a 

 small space, and we shall represent this 

 matter by a black square. In like man- 

 ner, we shall suppose that the whole of 

 the electric fluid contained in the same 

 body is condensed into a small space, 

 denoted by a white circle. The mutual 

 actions of the matter or electric fluid in 

 two adjacent bodies, are expressed by 

 lines passing from the one to the other 

 respectively ; the attractions being dis- 

 tinguished by unbroken lines, and the 

 repulsions by dotted lines. 



(234.) Fig. 44 represents a body B in 



Fig. 44. 



a neutral state of electricity, by which 

 is to be understood, that the quantity 

 of fluid it contains exists in a propor- 

 tion so exactly adjusted to the quantity 

 of matter, as that its repulsion for a 

 particle F of electricity at any distance. 

 precisely balances the attraction of the 

 matter for that same particle. "While 

 this equilibrium is preserved among the 

 forces which would impel any electric 

 fluid external to the body both from it 



and towards it, it is evident that the 

 body will neither acquire nor lose elec- 

 tricity, but remain quiescent, whether 

 it be insulated or not. 



(235.) The state of the forces ope- 

 rating between two similar neutral 

 bodies is shown in Jig. 45. Here it 



Fig. 45. 



follows from the condition of neutrality, 

 as above defined, that the two attractive 

 forces, denoted by the two whole lines, 

 are each of them equal to the repulsive 

 force between the two fluids, denoted 

 by the upper dotted line. Actuated by 

 these forces only, therefore, the two 

 bodies would attract each other. The 

 addition of a second repulsive force be- 

 tween the two portions of matter, as 

 represented by the lower dotted line, is 

 therefore necessary to account for the 

 state of equilibrium which we find, 

 under these circumstances, really ob- 

 tains. Some persons have conceived, 

 that by assuming the repulsive force of 

 the electric particles to be double the 

 attractive forces of the same particles 

 for matter, the equilibrium might be 

 explained without having recourse to 

 the mutual repulsion of the particles of 

 matter : forgetting, that such an as- 

 sumption is incompatible with that of 

 the neutral state of the bodies, which 

 is the condition under which we are now 

 examining them. 



(236.) The repulsion of two bodies, 

 each containing twice the quantity of 

 electric fluid requisite for the saturation 

 of their respective matter, is illustrated 

 byy?o-. 46. All the forces represented 



Fig. 46. 



