Double-Layer of Solid and Liquid Bodies, 299 



consists of a positive central nucleus of minute dimensions 

 and a cluster of electrons rotating about it. The correctness 

 of this conception, due to Rutherford, can hardly be disputed 

 at the present time. We may neglect the mass of the 

 electrons compared with that of the nucleus, and therefore 

 neglect the motion of the latter compared with thut of the 

 former. In other words, we may consider the nuclei as 

 immobile. 



Let us imagine a surface passing through the outermost 

 nuclei and call it, for the sake of brevity, the surface of the 

 body. One half of the electrons rotating around these 

 nuclei will remain outside this surface along with a lot of 

 other electrons belonging to nuclei which are situated within 

 the surface at a distance from it not exceeding the radius of 

 the largest electronic orbits. Wo may identify this radius, 

 corresponding to the " valency electrons," with the atomic 

 radius r. Thus a layer of thickness r within the surface 

 will be positively charged owing to part of the electrons 

 which belong to its nuclei remaining outside the surface and 

 forming there a negative layer of the same thickness r. 



This conception of an atomic electric double-layer is, as 

 will be shown, in remarkable quantitative agreement with 

 the experimental facts. Turning to the evaluation of the 

 intrinsic potential, due to such a layer, we shall first assume 

 each atom to consist (like a hydrogen atom) of a single 

 electron at a fixed distance r from an immobile nucleus 

 of charge +e, and calculate the mean electric density p x at a 

 given distance x from the surface (reckoned positive inwards), 

 all positions of the nuclei inside the surface and all orientations 

 of the atoms being equally probable. 



Fig-. 1. 



Let SSi (fig. 1) represent the surface of the body (supposed 

 plane). The planes AA 2 and BB 1? drawn at a distance +r 

 from SSx and parallel to it, will represent the limits of 

 positive and negative electrification respectively. 



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