58 H. NAGAOKA AND K. HONDA. 



the experiment on uvoids of ferromagnetic metals, and so to 

 extend the investigation into still stronger fields. 



2. In his well-known researches on the changes of dimensions 

 of iron and other metals by magnetization, BidwelP' pushed the 

 Held strength to loOO ; in the present experiment, the field 

 strength is greater than that of Bidwell by 700. In addition to 

 ordinary soft iron and steel ovoids, wolfram steel from Bohler 

 in Vienna was tested with a result which shoTved a remarkable 

 difierence from ordinary steel as regards the change of dimen- 

 sions wrought by magnetization. As Avas generally supposed, the 

 change of volume is very small in iron and nickel in weak 

 fields, but with strong magnetizing force the eftect becomes 

 generally pronounced. 



3. The apparatus already described w^as used in measuring 

 the change of length and of volume. A small alteration was 

 made in the arrangement of the magnetizing coil. Owing 

 to the strong magnetizing current, special arrangements w^ere 

 made for keeping the interior of the coil at a constant tem- 

 perature. A double walled tube of brass was inserted in the 

 coil, and a constant stream of cold water was passed in the 

 interspace for more than an hour l3efore each experiment. As 

 the resistance of the coil was only 0.56i?, the rise of temperature 

 was so small, that the ferromagnetics placed in its core w^ere 

 scarcely affected. The change of length was measured by an 

 optical lever, as before described."* For measuring the change of 

 volume, the ovoid was sealed in a glass tube with a capillary neck 

 (internal diameter about 0.4 mm.) and so placed in the tube 



1) Bidwell, Phil. Trans. 179, 205, 1889. 



2) Nagaoka. Phil. Mag. [5] 37, 131, 1894; Wied. Ann. 53, 487, 1894.; Nagaoka and 

 Honda loc. cit. 



