390 



ELECTRICAL MEASUREMENTS 



state at each reversal. Improved forms of secohmmeter have 

 been devised by Fleming and Clinton, and at the Bureau of 

 Standards. 



Galvanometer Battery 



H'l'l' 



FIG. 228. Showing connections for secohmmeter. 



The Impedance Bridge. Because of the nearer approach to 

 actual working conditions, capacity and inductance measure- 

 ments are now made by aid of alternating currents, preferably 



sinusoidal. 



Practically all the recent 

 researches on dielectrics and 

 condensers as well as the pre- 

 cision measurements of induc- 

 tances have been made by 

 bridge methods, using either 

 the impedance bridge or the 

 Anderson bridge. 



In the impedance bridge, 

 FIG. m-Meehcfogam for impedance which may fee ^jj^ to ^ 



measurement of either induc- 

 tance or capacity, there are four main conductors arranged as 

 in the Wheatstone bridge. Alternating currents are employed 

 and either two or four of the conductors are reactive. 



To deduce the condition for balance the arrangement shown 

 in Fig. 229 may be taken. 



