504 Mr. A. Campbell on the 



may prove o£ distinct value. The connexions are shown in 



fig. 3. 



Fig. 3. 



An iron ring is wound with superimposed primary and 

 secondary coils of turns N x and N 2 respectively, m being the 

 mutual inductance between them. These coils are connected, 

 as shown, through the coils of a mutual inductometer D to a 

 source of alternating current and a vibration galvanometer 

 (or tuned telephone), a sliding contact E allowing a part Q 

 to be selected from a resistance connected with the junction 

 of the coils of D. The galvanometer circuit is best made 

 highly inductive by a coil J. Let the hysteresis * and eddy 

 current loss in the ring be represented by a tertiary closed 

 winding, evenly distributed, of resistance E, and self induc- 

 tance L, having mutual inductances F and G to the primary 

 and secondary coils respectively. If Hi/N ? ==5, then Gr = 6F. 

 Let ti, i 2 , is be the instantaneous values of the currents in the 

 primary 5 secondary, and tertiary coils respectively, I l5 I 2 , 

 and I 3 being their effective values. Also let the current i t 

 be of sine wave form, which may be attained by electrical 

 tuning or otherwise, the period of the galvanometer being 

 also tuned to that of i x . The galvanometer deflexion can 

 now be reduced to zero by adjusting D and E to values M 

 and Q respectively. 



* If this be not considered rigorous enough for the hysteresis loss, the 

 part relating to it can be proved by another method. 



