A MAGNETIC CURVE TRACER 



23 



drum. The battery B-i supplies the field current, and Bz furnishes the 

 e.m.f. for the photo-electric cell, the value of the potential applied to 

 the latter being regulated by Ru The potential divider R3, and dry 

 cell Bu in series with the 10 megohm resistance i?o, are used to balance 

 out thermo-electric potentials and current from the photo-electric cell 



R6 

 0- 10,000^^ 



■AWc^W 



0-10,000*^ 



AMMETER 



Fig. 3 — Detailed diagram of the electrical connections. 



due to stray light. Ri and R-, are adjusted according to the amount of 

 flux in the specimen, in order to keep the maximum deflection within 

 the desired limits. The mutual inductance M is used to balance out 

 the potentials produced in S when no specimen is within it, so that the 



7750 



Fig. 4— Hysteresis loop of annealed iron. 



