402 Dr. C. V. Drysdale on the Use of the 



these figures. It will be noted that where the value o£ n is 

 less than about 1*38, K increases with an increase in tempe- 

 rature, while for greater values of n, K decreases as the 

 temperature increases. 



Flir. 8. 



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Values of n. 

 . The variation of K with temperature becomes greater as n 

 increases or diminishes from 1*38. 



Thus when n = l*80 (its mean value for a wr ought-iron 

 pipe), the mean variation in K is approximately 1 percent, 

 per 10° F. temperature variation. This rate of variation of 

 K with temperature decreases as the temperature increases. 

 The University, Manchester. 



XXXVII. The Use of the Potentiometer on Alternate Current 

 Circuits. By Charles Y. Dkysdale, D.Sc* 



OXE of the greatest inconveniences in connexion with 

 alternate current measurements has always been the 

 question of range. Owing to the fact that all instruments 

 employed for direct indication of alternate currents or P.Ds. 

 have a square law, their range is small and they become 

 impracticably delicate when low voltages are concerned* 

 There is therefore a very great need for some instrument 

 which, like the direct-current potentiometer, should be 

 * Communicated by the Physical Society : read January 22, 190J. 



