BABBITT. —THE VON WALTENHOFEN PHENOMENON. 239 



at L ; make the secondary again at L and reverse 0. The B calcu- 

 lated from this last throw will be in general different from the first B. 

 If one repeats the process, amounting to carrying the iron around the 

 hysteresis cycle, a sufficient number of times, it will be found that the 

 value of B will become constant or at any rate very nearly so. Instead 

 of computing B it will be just as satisfactory to compare directly the 

 throws of the galvanometer. This will be done throughout the work. 



Any one of the complete reversals just described will be referred to 

 as a 1-step reversal. A 3-step reversal will consist of the following 

 process. With a maximum of the flux in one direction at the start, the 

 current is broken by throwing over M and thus putting K in the cir- 

 cuit. After the introduction of resistance and the reversal of 0, M is 

 thrown back to the primary of the toroid. Finally the resistance just 

 introduced is cut out, by moving a rheostat arm, if it be in the rheostat, 

 or by short-circuiting a coil, if it be in one of the gaps. For each of 

 these three steps the flux change is recorded as a throw of the galvano- 

 meter. The angular displacement of the coil can be computed and 

 from the sum of these angles the corresponding single throw in centi- 

 meters. By correcting for leakage one has the single throw that can 

 be used as a basis for comparison. A 7-step reversal would consist of 

 seven steps between the two flux maxima, and so on. 



The result of carrying out such an operation is to go from one mag- 

 netic condition to another in a given number of steps. If the initial 

 conditions be twice the same and the final inducing field twice the 

 same, but the number of steps in one case diff'erent from that in the 

 other, there are at hand the means for determining, by comparing the 

 corresponding single throws of the galvanometer, what effect the num- 

 ber of steps has on a magnetic change. To satisfy the second of the 

 two conditions is a comparatively easy matter. The first is more 

 troublesome. However, if the iron be carried through a large number 

 of hysteresis cycles, until the maximum B for the cycle is constant, 

 a number of observations taken for 1-step reversals and then a number 

 for 3-step reversals, it is certain that for the first 3-step reversal the 

 initial conditions were the same as for the last 1-step reversal. Fur- 

 thermore, if the following 3-step reversals give the same result as did 

 the first 3-step reversal, it is fairly safe to assume that there has been 

 no change in the iron after the first 3-step cycle. For two low values 

 of H, 2.35 and 3.46, this process was carried out; the corresponding 

 maxima for B were 820 and 1394. 



In the first case, after the ballistic galvanometer was found to be 

 working with its usual accuracy (0.1 per cent), the iron was carried 

 through twenty-five 3-step reversals with a maximum field of 2.35. 



