214 Alternate Current and Potential Difference Analogies. 



between the P.D. at the terminals of fg and the P.D. at the 

 terminals of hj. Connect up the high-resistance dynamo- 

 meter successively as shown, and let d ± , d 2 , and d z be the 

 three deflexions obtained. 



Each circuit of the dynamometer consists of a coil of fine 

 wire, and a non-inductive high resistance in series with it. 

 Let r be the total resistance of each circuit, and let (/> be the 

 angle of lag between a current in either circuit of the dyna- 

 nometer and the P.D. at its terminals. 



Let V/ and Y/ be the maximum values of the P.D. between 

 /and g, and between h andy respectively, then 



d x cc 



d 2 cc 



cos 2 </> ? 





d 3 GG J ( — — COS X '—*- COS (f) J COS 0, 



COS 



e 



s/ 



16 did* 



Figure 13 shows the way in which the Blondlot and Curie 

 double-needle electrometer can be successively connected up 



so as to obtain, from the readings d h d 2 , d 3y the angle of 

 phase -difference between the P.D. at the terminals of fg, 

 and the P.D. at the terminals of hj, the formula being, of 

 course, 



COS0: 



v4 



d? 



xdo 



I we desire to measure the angle of lag between the cur- 

 rent in any circuit ah and the P.D. between its terminals, we 



