of Steel, Nickel, Cobalt, and Nickel-Steels, 



57 



filling the volumenometer may be caused by the pressure in 

 the magnetic field. To guard against this source of error 

 we have specially examined the volumenometer readings by 

 simply filling it with water or ferric chloride. The result was 

 in the negative within the range of field used in the present 

 experiment, as will be easily expected, since the pressure is 

 proportional to the square of the field strength. 



(a) Cast Steel (fig. 8). 



The metal shows increase of volume in fields up to <£j = 2000. 

 In weak fields the change is very small, but the rate is 

 tolerably large ; as the field increases the curve reaches an 

 inflexion-point. The change goes on somewhat slowly for 

 fields amounting to a few hundred units ; it again reaches 

 an inflexion-point, whence to increase steadily and almost at 

 a constant rate as the field is farther increased. * 



(b) Nickel (fig. 8). 



In our two former experiments we noticed a discrepancy 

 \a the nature of the volume-change in this metal. With a 

 bar of square section we noticed a diminution, while an ovoid 

 showed an increase. That this may be easily accounted for 

 we have already discussed in our former paper, so that it 

 would be unnecessary to enter into the subject anew. 



Fig. 8. 



With the present specimen, which may be considered as 

 more homogeneous, we noticed a slight increase of volume, 

 which is about the same in amount as that observed in the 

 former experiment. The character of the change is similar 

 to that in steel, the curve of the change presenting two 



