MAGXETIZATIOX OF MCKEL. 



299 



This seems to show that for uioderate strengths of field, the hjad 

 at which tlie wire begins to show reversed pularity, is nearly directly 

 proportional to the strength of the field. For very weak and strong 

 fields, this rule does not seem to hold. It must be remembered of 

 course tliat all these peculiarities are for one particular twist only, and 

 that it is possible that quite a different series of effects might exist for 

 other twists. 



The general results of these experiments may be thus summarised. 



In all mao-netic fields with moderate loadintr the effect of twisting 

 nickel wireis to increase the mngnetization. lîut the increase depends 

 on the strength of the field as ^vell as the longitudinal stress applied. 

 If the field is weak, and the longitudinal stress sufficiently great, the 

 magnetization increases in one direction of twist, and decreases in the 

 other. Eventually for a particular stress which is approximately 

 proportional to the field, the wire begins to show ojiposite polarity ; 

 and the cyclic curve of magnetization passes gradually from a two- 

 looped to a single looped form. For stnjnger fields similar effects 

 exist. But in fields higher than a critical value, the increase and 

 deci'ease of magnetization take place for reversed directions of twist, 

 and at the same time, the course of the curve becomes reversed. 



In a recent paper (Magnetische Untersuchungen, Wiedemann's 

 Annalen, March 1886) Professor Wiedemann has described certain 

 exjjeriments on the combined effects of magnetization and twist in 

 iron and nickel. He does not seem, howe\ er, to ha\e investigated the 

 effect of longitudinal stress in conjunction with these. His chief aim 

 seems to have been to adduce facts in support of his theory of friction- 

 all}' rotated molecules. Some of the results above described may be 

 expressed in terms of h\s theory. Thus when the external magne- 

 tizing force is great, the magnetic molecules will be held in position 

 more strongly and consequently, the change of magnetization due to 



