﻿58 Dr. C. Y. Burton on the 



Dewar and Fleming * on the resistance of pure unalloyed 

 metals at very low temperatures. In the case of all the pure 

 metals examined by these authors (platinum, gold, palladium, 

 silver, copper, aluminium, iron, nickel, tin, magnesium, zinc, 

 cadmium, lead, and thallium), the temperature-resistance 

 curves are almost straight lines, and these, being produced, 

 would pass very nearly through the point whose coordinates 

 are zero temperature and zero resistance. 



The same was not found to hold good for the temperature- 

 resistance curves for alloys; but if these curves could be pursued 

 far enough by experiment, they must be found, I think, to 

 terminate at the origin of coordinates, like those of the pure 

 metals. 



6. Dissipation of Energy in a Conductor conveying 

 a Current. 



In fig. 1 let A and B be two perfectly conductive particles 

 (whether molecules or parts of the 

 same or of different molecules we Fig. 1. 



need not consider), and let them be A *L 



approaching one another. Suppose — *\~) v J 4 — 



also that there is an applied E.M.F. 

 acting from right to left (as indicated ^ (pc 



by the large arrow) . Then, generally 



speaking, A will be negatively electri- _/Os f~\—^ 



fied, owing to a previous encounter " vJ/ v_y 



with some particle farther to the left, 



and for a similar reason B will in general be positively electri- 

 fied. When A and B collide, the usual effect is to leave A on 

 the whole positively electrified, and B negatively electrified. 



Remembering that the conductivity of A and B is perfect, 

 let us consider what transformations of energy are effected by 

 movements and collisions of this kind. Before the collision, 

 A being negatively electrified is urged towards the right 

 by the applied E.M.F., while B being positively electrified 

 is urged towards the left : that is, A and B are urged 

 together, and are gaining kinetic energy at the expense of the 

 source of applied E.M.F. After the collision, the electrifica- 

 tions are, generally speaking, reversed, so that A and B are 

 now being urged apart by the applied E.M.F., and continue 

 to gain kinetic energy as before. Further, when particles 

 such as A and B come into collision, so as to cause a re- 

 adjustment of their electrifications, and also when they are in 

 motion between two collisions, electromagnetic disturbances 

 will be produced in the intermolecular ether ; but since all 

 * Phil. Mag. Sept. 1893, p. 271. 



