CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



THE VON WALTENHOFEN PHENOMENON IN SOFT 



mON RINGS. 



Presented by B. O. Peirce, May 10. Received July 11, 1911. 



By Louis A. Babbitt. 



The purposes of the investigation described in this paper were two : 

 first, to determine how the manner of growth of a magnetizing field of 

 given final intensity about a mass of finely-divided iron affects the 

 change which the field produces in the magnetic condition of this iron ; 

 second, to harmonize the results found by previous observers in the 

 same field of inquiry. 



About fifty years ago von Waltenhofen ^ observed that when the field 

 in a solenoid used to magnetize a soft iron rod was suddenly reduced to 

 zero by breaking the circuit, the remanent magnetism of the iron was, 

 under certain circumstances, opposite in direction to that induced by 

 the field just applied. This result, interpreted by means of Weber's 

 theory of elementary magnets possessing inertia, led almost immedi- 

 ately to the conclusion that the magnetic condition of the mass of iron 

 is affected by the manner in which the magnetizing field is built up. If, 

 for example, the field were changed continuously in the same direction, 

 in one instance by two steps and in the other by one, firom one given 

 value to another, the one-step method should produce, according to 

 Weber's hypothesis, the greater magnetic change in the iron ; for the 

 greater velocity acquired by the elementary magnets under this method 

 would cause them to rotate through a greater angle, and shoWi^a greater 

 flux change in the metal. Similarly, a high electromotive force applied 

 to the magnetizing circuit should, through the more rapid magnetiza- 

 tion produced, give a larger magnetic change than a low voltage would, 

 even though the final value of the current is the same in both cases. 



From a commercial, as well as from a scientific point of view, this 

 phenomenon is important. The calculations which precede electrical 



* Pogg. Ann., 120, 650. Winkelmann, Hand, der Physik, 5, 214. 



