370 H. NAGAOKA AND K. HOXDA j 



Results in iron : — A few of the observed results with the iron ovoid 

 or cylinder are given in Figs. 9 and 10 (PI. XIX). The dotted lines 

 indicate the correction due to the change of volume by compression, 

 which must be added to the apparent change. These figures show that 

 there is only minute diminution of magnetization by the application of 

 hydrostatic pressure ; in fact, the apparent change measured in C.Gr.S. 

 units does not even amount to 0.1 with a pressure of 250 atmospheres. 

 At the above mentioned pressure, the change for H=54 is less than 

 2^^; of the intensity of magnetization. During a pressure cycle, there 

 is distinct hysteresis, arid the curve of the change of magnetization 

 generally forms a single loop. On account of the inconstancy of the 

 field, the measurement with the ovoid could not extend beyond H = 

 15 ; with the iron cylinder, H=54 was the strongest field, in which 

 the cyclic change could safely be observed. 



If from experiments of pressure cycles, the curves for constant pres- 

 sure in different fields be plotted, we obtain Figs. 11 and 12 (PI. XIX), 

 when the change of magnetization due to the contraction of volume is 

 not taken into account ; if the correction be applied, then we obtain 

 Figs. 13 and 14. These curves show that the range of the change in 

 magnetization due to pressure increases with the field ; the increase 

 takes place very rapidly at first, but becomes. asymptotic in n moderate 

 field. Plotting these changes against magnetization we obtain Fig. 15 

 which indicates that the change is nearly proportional to the intensify 

 of magnetization. 



Comparing these curves with those for the change of volume by 



magnetization, we find similarity bet ween the two. If is in- 

 teresting to note that whereas increase of magnetization produces 

 increase of volume in iron, diminution of volume produces diminu- 

 tion of magnetization. Thus n reciprocal relation between Hie strain 



