RESEARCHES ON MAGNETOSTRICTION. 



363 



These numbers plotted against H, I, and I 2 are shown in 

 Figures 1, 2, 3 (PL XVIII). Fig. 1 shows that the volume of iron 

 increases very rapidly at first with the magnetizing force, but it 

 soon reaches the ' Wendepunkt,' and then increases asymptotically 

 with further increase of the field strength. Fig. 2 shows that 

 the increase of volume takes place very slowly with the increase of 

 magnetization, but goes on very rapidly as the magnetization 

 becomes stronger. It will be seen from Fig. 3 that the increase of 

 volume is approximately proportional to the square of the intensity 

 of magnetization. 



Bid well found, from the measurement of the change of dimen- 

 sion of iron rings, that there is a diminution of volume in low 

 field, and experiments by Dr. Knott on the change of internal 

 volume seem to confirm this. In the present experiments with 

 ovoid or cylinder, we found no such diminution, but always in- 

 crease of volume in iron. Excepting in low fields, the change of 

 volume is in rough agreement with that of the tube of wide bore 

 used in Dr. Knott's experiments. 



The following table gives the determination of the change of 

 volume in the nickel rod. 



