134 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



ent values the largest of which (belonging to the curves C, M, N) was 

 about 82 : in this case the current was almost exactly 2.50 amperes. 

 Before each of the curves A, B, C was taken the core was thoroughly 



SECONDS 



Figure 28. 



Direct and reverse currents in a coil of 2788 turns belonging to the magnet 

 Q for three different values of the applied voltage, but the same value of r. 



demagnetized : R, P, M are direct curves, but 8, Q, N are reverse 

 curves. It is evident that the building-up times are not even approxi- 

 mately independent of E. 



Figure 29 shows the records of an oscillograph in a secondary circuit 

 in which were a few turns of wire wound around the core of the magnet 

 Q. The primary circuit contained, besides the storage battery, a rheo- 

 stat and an exciting coil of 1394 turns. 



When the primary circuit 



TIME. 



Figure 29. 



was suddenly closed with such a resistance in the rheostat that the final 

 strength of the current was 1.1 amperes, the induced current had the 

 value indicated by the curve Q; when the rheostat resistance was 

 suddenly removed so as to bring the final strength of the current up to 



