148 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



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

 rent curves, the whole change of flux due to a given current in the coil is 

 the same 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 



0.1 0.2 0.3 



Figure 42. 



SECONDS 



Theoretical form of reverse current curve for a coil of 1394 turns belonging 

 to the magnet Q, under an electromotive force of 208 volts. The resistance of 

 the circuit is 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 142, 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 slightly 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 



