- WILLIAM SIEMENS, J-.K.S. 



57 



:iiul since for 

 and 



_ ;!' the integration constant 6'= log. K 



y ~ *' 



or 



and 



*- 



In a regular cable 



log. 



or Kw = - 



A 



and 



and therefore 



and 



and therefore 



A 



/ log.| 



t 



E 



log. 



A.27T./ 



, E t\ 



** y - -T 



. (V.) 



X : 7 = log. - : t 



y 



This method is well adapted for ascertaining the specific re- 

 sistances of insulating materials, and to compare the insulation of 

 two similar cables, even when no instrument capable of exact 

 measurement is at hand. It suffices to observe the times required 



for the reduction of the original tensions to a given fraction. As 



p< 

 the proportion although unknown is in each case the same, it 



/ 



is obvious from the former formula that 



t\ 



I 



/, A, 



and 



