RESEARCHES ON MAGNETOSTRICTION. 373 



of negative pressure. It is to be remarked that a solid cylinder of 

 iron with the brass cap as shown in the above figure does not show 

 appreciable change of magnetization with the utmost pressure available 

 in the present experiment. 



The experiments indicate that the application of stress so as to 

 produce no shear affects the magnetization of iron or nickel only very 

 slightly, but the remarkable change in magnetization, produced by 

 tensional or compressional stress applied longitudinally, as well as that 

 due to twisting wrench, is always accompanied by the shearing strain — 

 a result, which will be of no small value in the theory of molecular 

 magnetism. 



§ 4. Effect of longitudinal pull on the magnetization 

 of iron and nickel. 



The above subject has been investigated by several ex- 

 perimenters, but so far as we are aware, the change in the magnetization 

 of iron and nickel by the application of feeble stress is scarcely known. 

 It will be seen from the experiments on the strains produced by 

 magnetization that the strain corresponds to the effect of a very feeble 

 stress. As our principal object in the present investigation was a 

 comparison of Kirchhoffs theory of magnetostriction with the ex- 

 perimental results, we found it necessary to pay special attention to 

 the change in the magnetic qualities of iron and nickel, when these 

 ferromagnetics are subjected to small longitudinal pull, which will 

 strain these metals to a degree comparable with the deformation in 

 the magnetizing field. 



As the iron ovoid used in the preceding experiment was unfit 

 for studying the effect of the longitudinal pull, an iron rod of 0.27 

 sq. cm. section made of the same material as the ovoid was used tor 

 measuring the chancre of magnetization in the free and in the feebly 



