74 H. NAGAOKA AND K. HOXDA. 



tlieso two metals lins been clearly establisliecl, altliongli there 

 is some difference in tlie field strength between iron and 

 nickel. It appears from the experiments of Dr. Knott'* that the 

 area of tlie hysteresis curve in the longitudinal magnetiza- 

 tion produced by twisting circularly magnetized wire reaches 

 a maximum as the field strength is increased ; but on account 

 of the feebleness of the current, the existence of the maximum 

 in the longitudinal ma2;netization is not well established. To 

 judge from the course of the curve given by the same experi- 

 menter, it seems highly probable that the maximum would be 

 reached if we could push the circularly magnetizing force a little 

 farther. The conclusion (3) is still an open question, although 

 some experiments of Matteucci'' seem to corroborate the view 

 just stated.'"^ 



1(S. Looking at the curves of /.•"//, we cannot but be struck 

 with the close resemblance of the curves representing the amount 

 of torsion produced by the combined action of the circular and 

 the longitudinal magnetizing forces on a ferromagnetic wire. AVe 

 can no doubt co-ordinate the effect of torsion on a magnetized 

 wire with the Wiedemann effect. The discussion of the last men- 

 tioned effect we hope to lay before the public in the near future. 



In spite of the qualitative explanations which Kirchhoff's 

 theoi-y afïbrds with regard to the efîect of longitudinal pull, of 

 the hydrostatic pressure, and of torsion, there are instances in 

 which tlie theory apparently fails in several quantitative details 

 that it necessarily calls for modification. We may remark that // 



1) Knott, Trans. Eoy. Soc. Edinb., 36, 485, 1891. 



2) Mattencci, Annales de Chimie et de Physique, 1858. 



•î) "While tliis jiaiier was passing through the press, we fcmnd that the direction of tlie 

 transient current prnduceil hy twisting a magnetized iron wire is reversed in strong magneti- 

 zing fields. 



