62 



BRIDGMAN. 



where AT" is the tension; and if the strains are produced by pressure 

 we have 



A5/ _ A5^ _ 1 1 /dr\ 



Substituting these expressions for the strains gives 



^ 1 1 /dv\ , 



and Kt = T. [ki — o-Av] 



where /Vt is the tension coefficient of resistance tabulated above, and 

 Kp is the pressure coefficient of resistance above. But since these two 

 coefficients are known experimentally, we have two equations to 

 determine, the two unknowns ki and kr. I have made the calculations 

 and tabulated the results in Table II. 



TABLE II. 



Let us now consider what sort of numerical values our theory would 

 lead us to expect. For a normal metal we expect ki to be positive, and 

 greater than unity, since in addition to the increase of resistance 

 brought about by increasing the distance apart of the atoms, there 

 is an increase due to the simultaneous increase of amplitude. Since 

 most of the electron paths have a transverse as well as a longitudinal 

 component, the same reasoning would lead us to expect that kr would 

 also be positive and less than ki, but of the same order of magnitude, 

 there being two transverse degrees of freedom against one longitudinal. 

 In the same way, we would expect that for bismuth, where the effect of 



