CHANGE OF VOLUME AXD OF LENGTH. 



71 



It thus appears that in nickel the effect of hydrostatic pressure 

 is very small compared to that of longitudinal pull. There 

 is increase of magnetization -with the volume contraction of 

 the magnet. Such an increase reaches a maximum in low 

 fields, whence the effect gradually diminishes. Similar changes 

 are also noticed in the case of iron and steel. In our former 

 experiment, we found that hydrostatic pressure increases the 

 magnetization in nickel, while it decreases it in iron. The 

 agreement between theory and experiment is very close in nickel, 

 but there is a wide di?icrepancy in iron and steel, as we have 

 already noticed. 



17. Effect of torsion on longitudinally or cireularhj magnetiz- 

 ed wire. There are other important consequences to be drawn 

 from the constant //' with regard to the effect of torsion on 



