BABBITT. — THE VON WALTENHOFEN PHENOMENON. 



231 



a slight modification of the usual procedure in step-by-step ballistic 

 measurements would give consistent results. Instead of keeping the 

 secondary circuit closed during the whole flux change corresponding 

 to a given step of the primary current, advantage was taken of the slow 

 movement of the amperemeter and, when the current had attained a 

 certain value in the primary, the secondary was broken. The flux 

 change up to that point was recorded with more or less accuracy. 



Figure 1. 



The iron was then carried on around its hysteresis curve, and, when the 

 primary current had reached the same value that it had at the instant 

 when the secondary was broken, the secondary circuit was again closed, 

 and it remained closed during the completion of the step of the pri- 

 mary current, thus giving a ballistic efl"ect which measured the change 

 of magnetic flux during the second part of the step in question. If 

 two minutes are required for the complete flux change and a galvan- 

 ometer with a period of five minutes be used, a division of the one step 

 into four parts instead of two as just described will give a result having 

 a probable error not greater than 0.4 of one per cent. The sum of the 

 four throws will give the total flux change in that step. The applica- 

 tion of this method to the various steps of an hysteresis curve will 

 give results of any desired degree of accuracy up to the limit of the 

 instrument. In fact, numerous tests showed that after the iron had 

 been carried through a cycle a large number of times two successive 

 cycles obtained in this way were equivalent both as a whole and in 

 their corresponding steps to within one half of one per cent. 



The three curves A, C, and D of Figure 2, corresponding to 4, 28 and 

 56 steps respectively, were obtained in the manner just described. The 

 maximum value of the magnetizing current and consequently the maxi- 



