212 Prof. Townsend on the Conductivity produced in 



As the variables extend over large ranges, the points 

 are given on two diagrams, figs. 7 and 8 ; one for values 



of —less than 320, and the other on a different scale for the 



larger values of the variables. The positions of the points on 

 the diagrams show clearly that they all lie on the same curve 

 so that the results of the experiments confirm the result to 

 which we have been led by theoretical considerations. 



Fiff. 7. 

































4- 

































< a 



5 





























y/% 































4 





























Sy 































X 3 





























/c 















2 















/ 





























) 



¥ 



















j 











A 



/ 



























/. 



y 



y + 3 























•5 



/_£ 



/ 



^<jl 



























20 



60 



120 



140 



200 220 



240 



280 300 



X -=-£>. 



The problem of determining a in terms of p and X is 

 therefore considerably simplified; and the three variables «, 



p, and X have been reduced to two : - and — . 



p p 



Before we proceed to determine the coefficients in equation 



7 we may here mention an interesting geometrical property 



of the curve (fig. 8). 



320 



