Transformer Indicator Diagrams. IG'J 



the sequel, we can obtain by its means the magnetizing- 

 current wave. ?iit\ + «gC 2 , with the same accuracy a* any of 

 the other quantities. 



Incidentally will be given new methods of comparing 

 mutual inductances, and of measuring both mutual and self 

 inductances in terms of a resistance and a time. 



2. In the paper just quoted I have shown that if a periodic 

 current C flows in the primary of a pair of coils who.-e 

 mutual inductance is M, and if the secondary be joined 

 through a suitably arranged commutator (running synchron- 

 ously with the generator of the periodic current), which 

 commutes twice per period, to a large resistance r and thence 

 to a galvanometer, there will be a steady deflexion y in the 

 latter which is connected with the instantaneous value C of 

 the periodic current at the instant of commutation by the 

 relation 



where \ is the reducing factor of the galvanometer and T 

 the period. 



Bv arranging so that the commutating brushes can be 

 rotated on a divided circle round the drum of the commutator, 

 commutation can be effected at any desired instant of the 

 period, and the corresponding galvanometer reading when 

 multiplied by the factor given in the above equation gives 

 the ordinate of the current wave at that instant. 



Take now a triad (see fig. 1, T) of coils of which p 1 and p 2 

 are to serve as primaries and the remaining one s placed 

 between p 1 and p 2 to serve as common secondary. Let s be 

 connected as before through commutator and resistance r to 

 the galvanometer, and let Mj be the mutual inductance of jh 

 and s, and M 2 that of p 2 and s. Then, when a current C x 

 circulates in p± and none in ^ 2 , the galvanometer deflexion y± 

 produced is connected with the ordinate of Ci corresponding 

 to the instant in the period at which commutation takes 

 place by the equation 



and when a current C 2 , equiperiodic with C l5 circulates in 

 p 2 and none in p x , a galvanometer deflexion y 2 is produced 

 which is similarly connected with the corresponding ordinate 

 of C_ 2 by the equation 



