﻿Mechanism of Electrical Conduction. 57 



is of no moment in electrostatics. On the other hand, both 

 Ampere's theory of magnetism and Weber's theory of dia- 

 magnetism suppose the existence oi perfectly conductive particles, 

 and are thus strongly supported by our result. 



In discussing Weber's theory of diamagnetism, Maxwell* 

 points out that the currents excited in a perfectly conductive 

 body by any external cause are entirely confined to the surface 

 of the body. Thus the perfectly conductive bodies in Theorem I. 

 may be replaced by perfectly conductive surfaces, without 

 altering any of our conclusions ; but it would be hard to 

 decide whether a perfectly conductive geometrical surface is 

 or is not a physical possibility without knowing more of 

 electromagnetism — not to speak of ordinary matter. 



4. Theorem II. 



In metals, and in other non- electrolytes whose conductivity is 

 finite, the transmission of currents must be effected by the inter- 

 mittent contact of perfectly conductive particles. 



For if there were not these intermittent contacts, any given 

 two of the conductive particles would be either permanently 

 in contact with one another, or permanently out of contact, 

 and there would be only two cases to consider. If through- 

 out the substance there extended continuous chains of (per- 

 fectly) conductive particles in contact with one another, the 

 substance as a whole would be a perfect conductor ; while in 

 the absence of such chains of particles, the substance would 

 be a perfect non-conductor. Finite conductivity can only 

 exist when the contacts are intermittent. 



5. An immediate corollary is 



Theorem III. 



If we suppose that in a substance at the absolute zero of 

 temperature there is no relative motion amongst the molecules or 

 amongst their appreciable paints, it follows that every substance 

 at this temperature must have either infinite specific resistance 

 (which need not imply infinite dielectric strength), or infinite 

 conductivity. 



For the denial of relative motion involves the denial of that 

 intermittence of contact which in Theorem II. was shown to 

 be necessary to finite conductivity. 



This conclusion is in accordance with the experiments of 



* ' Electricity and Magnetism,' 2nd ed. vol. ii. § 840. 



