of Electricity through Metals. 193 



removed, while below it the current may persist for days 

 without undergoing any considerable diminution. It seems 

 to me that this is another, and fatal objection to the theory 

 that metallic conduction is due to the presence in the metal 

 of free electrons which drift under the electric force, for no 

 permissible increase in the number of free electrons or in the 

 mean free path would explain the difference between the 

 ordinary and super-conducting state. In the case of the lead 

 ring the maximum free path (equal to the longest chord that can 

 be drawn in the ring) cannot be more than a few millimetres. 



It is the object of this paper to show that the effects 

 discovered by Kamerlingh Onnes are in accordance with 

 the theory of Metallic Conduction which I gave in 'The 

 Corpuscular Theory of Matter ' (page £6), and which, with 

 the substitution of an electron for a charged atom, is sub- 

 stantially the same as that given in my ' Applications of 

 Dynamics to Physics and Chemistry/ 18o'8. 



On this theory, the atoms of some substances, including 

 the metals, contain electrical doublets, i. e. pairs of equal 

 and opposite electrical charges at a small distance apart. 

 In the normal state of a body the axes of the large number 

 of doublets occurring in even a small volume are uniformly 

 distributed in all directions : when, however, an electrical 

 force acts on the body, the axes of the doublets tend to point 

 in the direction of the force and the moments of the doublets 

 have a finite resultant in this direction. It the axes of the 

 doublets were quite free to set in any direction, the smallest 

 electrical force would be able to pull the axes of all the 

 doublets into line and thus produce the maximum polarization. 

 There are, however, several influences at work which limit 

 the number of doublets which point in the direction of the 

 •electric force. 



In the case of gases, for example, there are collisions 

 between the various molecules which tend to knock the axes 

 of the doublets out of line as fast as they are brought into 

 it by the electric force. Langevin has calculated from the 

 principles of the Kinetic theory of Gases the magnitude of 

 this effect, and has shown that if M is the moment of each 

 doublet, N the number of doublets in unit volume, I the 

 resultant of these moments parallel to <r, and X the force on 

 a doublet in this direction, 



1 €*-€-* JC) 



when .r = MX/K0, 



6 being the absolute temperature and 1\6 the mean kinetic 

 Phil. Mag. S. G. Vol. 30. No. 175. July 1915. 



