148 



EKDINGS uF THE AMERICAN ACADEMY. 



of eddy currents are very noticeable at the early portions of most cur- 

 rent curves, tin' win ile change of tlux < hie to a given current in the coil is 

 the Bame apparently whether the current grows steadily or by steps; in 

 this case an accurate diagram of the U form and a step-by-step ballis- 

 tic method with a proper galvanometer may be expected to yield 



0.2 0.3 



FlGI RE 12. 



SECONDS 



Theoretical form of reverse current curve for a coil of 1894 turns belonging 

 tn the magnet Q, under an electromotive force of 2<i8 volts. The resistant 



the circuit IB 160 ohms. 



identical results within the limits of the measurements. This state- 

 ment seems to be justified by such comparisons of the two as that 

 recorded on page 1 l_, which required many days in the making. From 

 a current curve we may expect to get a hysteresis diagram good enough 

 for any commercial purpose, but differing slightby at the beginning 

 from the statical diagram found ballistically. Of course, it would 

 not be easy to get any very accurate information, as some of the curves 



