3(34; H - >~AGA0KA AND K. HONDA; 



Nickel always shows diminution of volume, and the change is 

 greater than in iron. From Figs. 4, 5, 6, we gather the following- 

 facts : in low fields the diminution of volume is at first very slow, 

 and then rapid, until it reaches the ' Wendepunkt,' where it becomes 

 steady though slower. 



As determined by external measurements, the diminution of the 

 volume of nickel with feeble magnetization is very slight, but it 

 becomes very rapidly greater as the magnetization is made stronger, 

 so that the change is nearly proportional to the square of the magnetic 

 intensity. This is contrary to what Dr. Knott found as regards the 

 initial behaviour of nickel which, according to him, increases in 

 volume in low fields, and although our observations in high fields 

 agree with his as to the quality of the change, they yet indicate the 

 change in volume to be nearly ten times less than he made it out to 

 be. It is to be noted however, that whereas our measurements of the 

 volumes have been external, his were made on the changes in the 

 internal capacity of a nickel tube. 



§ 2. Change oflength by magnetization. 



It would be superfluous to give minute details of the measure- 

 ment of the change of length by magnetization. The apparatus was 

 the same as that used by one of us 1} some years ago in the investiga- 

 tion of the effects of hysteresis on the change oflength. It consisted 

 of a simple optical lever with an arrangement for temperature com- 

 pensation on the same principle as the grid-iron pendulum. The 

 mirror described in the former paper was, this time, replaced by a small 

 total reflecting prism. 



The measurements of the change of length in iron and nickel are 

 given in the following table with corresponding values of H and I. 



1). Nagaoka, Phil. Mac/. 37. 131, (1S94); Wied. Ann. 53. 4S7, (1SD4). 



