90 ELECTRICAL MEASUREMENTS 



by a coil upon another placed in a parallel plane, their axes being 



coincident. 



An absolute current balance of this sort was used by Lor 

 Rayleigh and Mrs. Sidgwick, 1884, in their determination of the 

 electrochemical equivalent of silver. Since that time the instru- 

 ment has been brought to a very high degree of perfection, par- 



Three Supports like this 

 rePUoedl20Apart 



lead ot 180 as shown 



FIQ. 48. Absolute current balance used at Bureau of Standards by Rosa 

 Dorsey and Miller. 



ticularly through the work of Ayrton, Mather and Smith at the 

 National Physical Laboratory in England and of Rosa, Dorsey 

 and Miller at the Bureau of Standards at Washington, D. C. 16 



Rayleigh, and following him, Rosa, Dorsey and Miller used a 

 balance with two equal fixed coils, the smaller movable coil being 

 placed midway between them, all three coils being coaxial. 



The Rayleigh current balance is not intended for general use 

 as a current-measuring device, but for the absolute measurement 



