Potentiometer on Alternate Current Circuits. 



40: 



capable of measuring P.Ds. and currents of any range with 

 accuracy. It would also be a great convenience if tins 

 instrument were capable o£ indicating the phase as well as 

 the magnitude of the P.D. or current tested. 



In attempting to apply the potentiometer principle to 

 alternate current measurements, two processes seem to be 

 possible — (a) the balancing of the alternate current P.D. 

 against an equal direct current P.D. by the employment of 

 some differential balancing device preferably of an electro- 

 static character, or (b) the balancing of two alternate current 

 P.Ds. against one another. Such propositions as have 

 hitherto been made for an alternute-current potentiometer 

 have, the writer believes, always been based on the former 

 idea, owing to the fact that the latter principle would involve 

 equality of phase as well as of P.D. in the two voltages 

 compared. He understands that some time ago Mr. Swin- 

 burne suggested the use of a differential electrometer in 



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POTENTIOMETER. 



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STANDARD CELL. fl.C. P.D. V, . 



connexion with a potentiometer, but has not seen any 

 details. An obvious device would be that shown in hV 1 



