RELATIONS TO OTHER SCIENCES 125 



according as the intensity of the electric field is supposed to present, 

 or not, a discontinuity when it crosses the surface which limits the 

 volume occupied by the electron. Inertia, of electromagnetic origin, 

 which we are about to refer to a similar centre, is opposed also, under 

 the difficulty of its becoming infinite, to the hypothesis of a finite 

 electric charge condensed in a point without extension. 



The various considerations, more and more precise, all converging 

 toward this notion of the atomic structure of charges, form the start- 

 ing-point of all recent works on electricity. 



II. The Atom of Electricity 



(6) The Electron. The remarkable laws of electrolysis discovered 

 by Faraday establish an intimate and necessary connection between 

 the atomic structure of matter and that of electricity. They were 

 sufficient to lead Helmholtz to conceive the latter as constituted of 

 distinct, indivisible portions, elements of charge, all identical from 

 the point of view of the quantity of electricity which they carry, and 

 differing only in the sign. This elementary charge is equal to that 

 carried by a monovalent atom or radical in electrolysis; a polyvalent 

 atom or radical carries an equivalent number of such charges. 



It was Johnstone Stoney who first used the word electron to desig- 

 nate atoms of electricity as distinct from matter, with which they 

 combine to furnish the electrolytic ions. The presence of similar 

 electrons combined with material atoms allows us to represent certain 

 peculiarities of the spectrum, the existence of doublets of like fre- 

 quencies; the electron, in motion, is thus considered as the origin 

 of the emission of all luminous rays. 



(7) Gaseous Conductors. But there are the researches on the 

 electrical conductivity of gases, which have presented to us in a 

 forcible manner the idea of electrical atoms, which have made this 

 notion more tangible by allowing us to count these electric centres, 

 to lay hold of them individually, and to measure for the first time 

 the charge of each of them in absolute value. 



As early as 1882, Giese, in observing the peculiarities of the con- 

 ductivity of gases escaping from flames, the departure from Ohm's 

 law, the impossibility of drawing from the gas, whatever might be 

 the electric field employed, more than a limited amount of electricity 

 of each kind, the progressive recombination of the free charges in the 

 gas, had expressed in a precise manner the idea, that as in electrolytes 

 the free electric charges in a gas are carried by distinct positive 

 and negative centres in limited numbers, capable of moving in oppo- 

 site directions under the action of an external electric field in order 

 to discharge the electrified body which produces the field. 



It is difficult, in fact, to conceive how, on the hypothesis that the 



