ELECTRICITY. 



139 



lie succeeded, in company with some members of the Academy of Sciences. 

 There appears, nevertheless, to remain some doubt as to the share which 

 Volta really had in this famous experiment, since, in the account of it pub- 

 lished by Lavoisier and Laplace, it is related as performed by them, and Volta 

 is mentioned incidentally as being present on the occasion.* 



After the phenomena of electricity had, by the labors of Coulomb, been re- 

 duced to exact numerical estimation, this branch of physics was in a state to 

 permit its being brought within the pale of mixed mathematics. To accom- 

 plish this it was necessary to express, by mathematical formulae, the intensity 

 of the electric fluid on different parts of insulated conductors of given forms, 

 placed either separately, or in such a position as to exercise an electrical in- 

 fluence upon each other without contact, or, finally, when placed in actual con- 

 tact. To establish such formulae, it was necessary to assume some definite 

 hypothesis as the law of electrical action. The Franklinian theory of a single 

 fluid appeared to be incapable of affording the means of explaining, with numer- 

 ical precision, the state of such bodies. It is true that this long-received hy- 

 pothesis was sufficient to account, in a general way, for the electrical state of 

 bodies under the ordinary circumstances of their mutual action ; but when rig- 

 orous numerical accuracy was demanded when not merely the general cir- 

 cumstances of the dense accumulation of electricity in one part of the surface, 

 its more feeble intensity at another, its total abstinence from a third place, 

 or the presence of negative electricity on a certain side of a conductor, and pos- 

 itive electricity on another, were severally demanded ; but when it was required 

 to determine the exact numerical measure of the depth of the fluid at each particu- 

 lar spot on a given insulated conductor, placed under given conditions with ref- 

 erence to others, so that such numerical measure, so obtained by calculation, 

 might be compared with the actual depth observed by the instruments invented 

 and applied by Coulomb, then this theory appeared to fail ; at least, none 

 of its advocates produced any such calculations. Laplace investigated, on 

 mathematical principles, the distribution of electricity on ellipsoids of revolu- 

 tion, assuming, as the basis of his reasoning, the hypothesis of two fluids. Biot 

 also investigated the same problem applied to spheroids of small eccentricity ; 

 but the general subjugation of this portion of electrical science to mathematical 

 analysis is due to Poisson. 



This illustrious analyst took as the basis of his investigations the theory of 

 two fluids proposed by Symmer and Dufaye, with such modifications and addi- 

 tions as were suggested by the researches of Coulomb. He regarded the 

 mutual attractions and repulsions exhibited by electrified bodies, not as real 

 forces exercised by those bodies, but as altogether due to the electric fluids 

 with which they are charged. The laws of attraction and repulsion devel- 

 oped by Coulomb are therefore assumed as those of the electric fluids. The 

 particles of each of these fluids are assumed to repel each other with a force 

 varying according to that law, while the particles of each fluid attract those of 

 the contrary fluid by a force governed by the same law. These conditions 

 are sufficient to supply the mathematical formulae necessary to the determi- 

 nation of the depth and quality of the electric fluid on every part of the surface 

 of a body of given figure placed under any given electrical conditions. The 

 electric fluids of either kind would, by virtue of their self-expansive property, 

 escape from the surface of the body on which they rest ; but this is prevented 

 by the pressure of the surrounding air, which retains them in their position so 

 long as their expansive force is less than that pressure. On bodies of elonga- 

 ted forms, or those which have edges, corners, or points, it is shown, as a con- 

 sequence of this theory, that the electric fluid accumulates in greater depths 



Eloge de Volta, p. 21. 



