736 Mr. W, A. Jenkins on the Effect of a 



current. The resistance would be altered i£ the velocity 

 of the corpuscles carrying the current were to change. 

 Such an alteration of velocity might result upon a re- 

 arrangement of the atoms. From such a re-arrange- 

 ment one might expect slight velocity changes but not 

 changes of the order 10~ 2 . As the velocity of the corpuscle 

 is that due to its intrinsic energy and is not caused 

 solely by its being pulled out of the atom by an adjacent 

 atom ; such changes of velocity could not be expected as the 

 dimensional change is only of the order 10~ 6 or 10~ 5 . 

 From the equation 



R = — 



nXv ' 



we see that a decrease in n, i. e. the number of free corpuscles, 

 would give an increase in R. The specific resistance is 

 given by 



_ 4^ 

 /3ne*\v 



By calculation A, is found to be 7 x 10" 9 approximately, 

 and substituting the known values for the other quantities 

 we find that n is of the order 10 32 . Thus to produce an 

 alteration of the magnitude observed would require an 

 absorption of 10 3 ° corpuscles, when a fairly strong magnetic 

 field was applied. This means that each atom must absorb 

 10 7 corpuscles, which is unthinkable. The high value of n 

 is of course improbable from considerations of specific heat. 

 None of the factors therefore give a satisfactory explanation 

 of the resistance change. 



On the second theory of conduction the specific resistance 

 «is given by 



which reduces on substitution of known values to 

 R= 1 



3-5xl0- 12 p6 



where p is the number of corpuscles discharged per second 

 per atom and b the distance between the centres of the 

 doublets. The change in "&" will be of the same order as 

 the dimensional change and can be neglected in discussing 

 the resistance alteration. Variation of "jp" is the most 

 likely cause of the resistance change. Substituting for " b " 



