648 PROCEEDINGS OF THE AMERICAN ACADEMY. 



that if the iron core has been already magnetized in the normal direc- 

 tion by a current which has been slowly brought to zero, anomalous 

 magnetization does not occur when a second current is applied in the 

 same direction and then suddenly stopped, runs counter to all our 

 experiences. Specimens which have not been really demagnetized 

 show, of course, all sorts of abnormal behavior, but we have found it 

 easy, with suitable cores, to get reversals after a slowly applied current 

 has been slowly removed, by breaking suddenly a current in the same 

 direction whether this last was applied slowly or suddenly. If a 

 quickly applied current has been slowly cut off, we can get reversals 

 by quickly breaking a current in the old direction, applied either 

 quickly or slowly. If we apply either slowly or quickly a current in a 

 fixed direction, then open it suddenly, and repeat this process a score 

 of times, the reversal usually occurs at every break of the circuit with- 

 out any reversal in direction of the exciting current. The remanent 

 magnetism after a slow break, is greater if the current was quickly 

 applied, but, as we have seen and as Wiedemann's statements would 

 lead us to expect, anomalous magnetism occurs more regularly if the 

 current has been slowly applied. 



As Righi pointed out in 1880, if one cuts a number of pieces of dif- 

 ferent lengths from a stout steel rod and, beginning with the longest 

 and taking them in order, tests the sign of the remanent magnetiza- 

 tion of each after the exciting field has been suddenly destroyed, one 

 often arrives at a length where anomalous reversals begin and continue 

 for shorter pieces. Figures 9, 10, 11, are founded upon a set of such 

 tests made upon rods cut from the very soft bar which furnished the 

 specimen to which Figure 4 belongs. The diameter of the bar was 

 about 2.83 centimeters, and the lengths, in centimeters, of the pieces 

 used were 40.1, 31.8, 20.9, 18.0, 13.6, 12.0, 10.0, and 8.0. Figure 9 

 shows the residual fluxes through the centres of the pieces for all the 

 specimens except the first and the fifth. These are all reversed in sign, 

 but the amounts are extremely small because of the remarkable softness 

 of the material. The horizontal unit corresponds to a solenoid field of 

 20 gausses, the vertical unit is about 7 maxwells. The first piece, 40 

 centimeters long, showed a slight reversed moment for excitations in 

 the solenoid up to about 38 gausses, but the ordinates of the positive 

 loop were not so high as the other curves of the series might lead one 

 to expect them to be. Figure 10 shows the residual fluxes after the 

 exciting currents had been slowly reduced to zero. The horizontal unit 

 is here 80 gausses and the vertical unit 30 maxwells. Figure 11 shows 

 the induction fluxes through the cross sections of the rods while they 

 were in the magnetizing fields. The horizontal unit is in this case 80 



