ELECTEICAL MEASUREMENTS 



327 



on the impedances of the two circuits, as other things being equal the 

 smaller current should go through the hanging coil. 



Experiments. The coils used in the experiments were coils P lf P 2 , 

 C, B 1} B 2 , and A, which coils are described on page 315. From the 

 dimensions of P 2 and its self-inductance as found by method 25, B t was 

 designed to have a self-inductance of one henry. This will be shown 

 to be nearly the case. For ease of comparison B 1 has been taken in 

 the calculations of the results as being equal to one henry, and the 

 other coils were compared with this coil as a standard. 



In these experiments the connections were made as in the figure 7, 

 the coil BI that was taken as the standard being placed in circuit with 

 the fixed coils of the electrodynamometer as L" and the resistance of 

 this circuit was unaltered during the experiments in any particular 

 series. The coils whose self-inductances were to be determined were 

 placed in the hanging coil circuit and the resistance R was changed 

 until there was no deflection. The resistance of the two circuits, R" 

 and R -{- r were then measured by a Wheatstone bridge. 



The resistance r was in all cases small in order that (7 ibt should be 

 large, and therefore by induction <7 1 *< M +*> the current through the 

 fixed coils was made large and the instrument sensitive. The method 



