422 Mr. J. Larmor on the Molecular 



All sources produced the same result. 

 The mean of all experiments performed was 

 1 Siemens unit=0*94356 ohm; 

 or, one ohm is equivalent to the resistance of a mercury- 

 column having a section of 1 square millim. and a length of 

 105-98 centim. at 0° Centigrade. 

 Of the values determined, 



the lowest was 1 Siemens unit =0*94323 ohm, 

 the highest was 1 Siemens unit =0*94380 ohm. 



XLIX. On the Molecular Theory of Galvanic Polarization. 

 By J. Labmob, Fellow of St. Johrfs College, Cambridge*. 



1. "TT was first pointed out by Varley and Sir W. Thomson 



J- that the polarizing action of a galvanic cell may be 

 explained by considering the cell to act as an electrical con- 

 denser of very large capacity. The mechanism of this action 

 has since been examined in detail, especially by Helmholtzf. 



In the polarization of a water- voltameter with platinum 

 plates for electrodes, the action according to Clausius's well- 

 known molecular theory consists in the transfer through the 

 fluid of the temporarily dissociated hydrogen and oxygen 

 constituents under the action of the electric force ; so that in 

 the course of time a layer of hydrogen particles with their 

 positive charges accumulates in the immediate neighbourhood 

 of the kathode plate, and the complementary layer of oxygen 

 particles with their negative charges at the anode. 



Each of these layers will form a sheet, with positive or 

 negative charge, lying close to the metal plate. On the plate 

 will therefore appear an equal and opposite charge by induc- 

 tion. There is thus a double electric layer formed at each 

 electrode ; the charged particles forming one side of it being 

 prevented from coming up to and discharging themselves in 

 contact with the metal, in obedience to the electrical attrac- 

 tion, by chemical forces of repulsion. 



A double layer of this kind forms an actual condenser, 

 whose capacity is inversely proportional to the distance 

 between its faces. , And Gauss's well-known theorem relating 

 to magnetic shells shows, when applied to this case, that the 

 effect of such a condenser is to cause a sudden rise or fall of 

 potential in passing through it without producing any change 

 in the distribution of the electric force in the neighbourhood. 



* Communicated by the Author. 



t See his Wissenschaftliche Abhandlungen, vol. i., section Galvanismus, 

 and his Faraday Lecture, in the Journal of the Chemical Society for 

 1882. 



