386 



ELECTRICAL MEASUREMENTS 



or 



r> 



CY = CP ^~ as before. 



(13) 



Maxwell Method for Comparing Inductances. An induct- 

 ance may be compared with a variable standard by an analogous 

 method due to Maxwell.* 



The arrangement of the circuits is shown in Fig. 226. As 

 before, R M and R N are adjustable non-inductive resistances. 

 L x and L P are the inductances to be compared ; they have resist- 

 ances R x and R P respectively. In order to make the adjust- 

 ment expeditiously, it is necessary to include a variable non- 



6 



FIG. 22G. Mesh diagram for Maxwell method for comparing inductances. 



inductive resistance, R, which can be thrown into the arm 

 L x if necessary, by changing the battery lead from c to e and to 

 use for L P a variable standard of inductance having a constant 

 resistance. 



The adjustment is made in two steps; a probable value of the 



r> 



ratio -5^ is chosen, and keeping KI closed, the resistance R is 

 KN 



adjusted until balance is obtained. In this case the arrange- 

 ment is an ordinary Wheatstone bridge, only the resistances 

 coming into play. When the adjustment is complete, 



RN RP ~\~ R 



After the balance has been effected, KI is released and K% kept 

 closed. L P is now varied until the detector gives no indication 

 when contact is made and broken at KI. Then 



* "Treatise on Electricity and Magnetism," third edition, Art. 757. 



