Croo'k — Electromagnetic Alterncttincj Currents. 135 



eighth of that due to a current of the same current density 

 flowing directly through the iron strips in multiple. 



The yoke, fig. 2, used was one designed by Prof. D. B. 

 Brace and already described.^ 



The advantage of this apparatus over the old form of yoke 

 is that at all times during the hysteresis test the total induction 

 can be measured without changing the susceptibility of the 

 magnetic circuit, and the only change in the induction is that 

 caused by a change of current in the magnetizing solenoid. 



Diagram I. 



TTp^mimmg^TrTTTTT^Tf^^ 



itM}iz£l''"~Jl^ 



^i 



m^^ 





The alternating current used for demagnetization was 

 obtained from a 50-volt circuit, transformed from a-1000 volt, 

 40 h. p. Westinghouse dynamo. The frequency of the alter- 

 nating current was 133 periods per second. 



The three hysteresis cycles given on Diagram I were all taken 

 the same evening and nnder practically the same conditions. 



*This Journal, vol. xi, p. 365, May, 1901. 



