i58 Mr. R. Appleyard on Dielectrics'. 



Appendix II. 



Change of Dielectric-resistance with Temperature. 



Let the resistance at some fixed temperature be R ; and 

 iet R 1} R 2 , R 3 , &c. be the resistances at 1°, 2°, 3° . . . above R. 



The assumption is that the resistance diminishes -th of itself 

 1 n 



for every 1° rise of temperature. In this case, 



Ri = R- — j 



n 



and 



Ro = Ri • 



n 



Or, putting in the value of n, 



R s=TT 



Hence 



and, generally, 



R - R (|)' (2) 



If t and 6 are any two values of t, we have 



R T =R,(§) T ~ e ; • • • • • • (3) 



, /RxX logR — logR. 



By putting observed values of R., R fl , t, and 6 in this last 

 expression, the value of f~ J may be found, and substituted 

 in (3), which then becomes the working formula. In the 

 paper, I ^j ) is represented by a. 



Comparison of a for Centigrade and Fahrenheit Scales.— Let 

 R x be the resistance 1° 0. above that at which R is measured. 

 Then, by the preceding, 



•■-m 



