CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



THE ANOMALOUS MAGNETIZATION OF IRON AND 



STEEL. 



Bt B. Osgood Peirce. 



Presented May 10, 1911. Received January 2, 1912. 



In 1863, von Waltenhofen, who had been making experiments upon 

 the retentiveness of bars of iron and steel for magnetism, discovered 

 the phenomena which usually bear his name. If an increasing current 

 (/), ending in the maximum value /', be sent through a long solenoid, 

 the final value of the magnetic moment of a solid bar of originally de- 

 magnetized soft iron or steel within the solenoid frequently depends, 

 not only upon the final strength of the current, but also upon the man- 

 ner of growth of the current in attaining this intensity. The moment 

 will be greater if the current be suddenly applied in full strength than 

 if it be made to grow slowly, either continuously or by short steps. If, 

 after the current has remained steady for a short time, at the strength 

 /', it be made to decrease to zero, the residual moment of the bar will 

 usually be less if the current be suddenly opened than if the decrease 

 be made slowly, by gradually introducing more and more resistance, 

 and the demagnetizing factor of a given cylinder is considerably less 

 when computed from observations made by the method of sudden re- 

 versals, than if it is determined by slow, step-by-step changes in the 

 exciting current. 



Von Waltenhofen also encountered some cases of apparently anoma- 

 lous magnetization which he describes in the following words taken from 

 his paper in Volume 120 of Poggendorff's Annalen : 



"Es ist mir oft aufgefallen, dass die magnetischen Riickstiinde in 

 weichen Eisenkernen bei wiederholter, ganz gleicher, temporJirer Mag- 

 netisirung desselben Stabes, sehr ungleich ausfallen. Noch befrem- 

 dender aber war mir eine Erscheinung, die ich an einem sehr dicken 

 Eisencylinder zuerst wahrgenommen habe, und welche darin bestand, 

 dass der nach Aufhebung des magnetisirenden Stromes zuriickgeblie- 



