330 Messrs. Nagaoka and Honda on Change of Volume and 



showed a remarkable difference from ordinary steel as regards 

 the change of dimensions wrought by magnetization. As 

 was generally supposed, the change of volume is very small 

 in iron and nickel in weak fields, but with strong magneti zing- 

 force the effect becomes generally pronounced. 



Method of Experiment. 



The same apparatus as before described was 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, a special 

 arrangement was provided for keeping the interior of the coil 

 at constant temperature. 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 before each 

 experiment. As the resistance of the coil was only 0*56 ohm, 

 the rise of temperature was so small that the ferromagnetic 

 placed in its core was scarcely affected. The change of 

 length was measured by means of an optical lever, as before 

 described *. For measuring the change of volume, the ovoid 

 was sealed in a glass tube with capillary neck (internal 

 diameter about 0*4 mm.), and so placed in the tube that it 

 rested in the axial line, and never came in contact with the 

 wall of the tube. The magnetizing-coil and the tube were 

 placed horizontal. The motion of the meniscus was measured 

 by a microscope provided with micrometer ocular. For the 

 minute particulars we must refer the reader to the former 

 paper on magnetostriction. 



The following are the dimensions of ovoids used in the 

 present experiments : — 



Specimen No. 



1 



2 



Metal. 



a (cm.). 



c (cm.). 



v (c.cm.). 



P- 



N. 



Nickel 



0-750 



0-500 



12-50 

 1000 



31-50 

 10-48 



8-86 

 8-86 



0-125 

 0-0848 





3 



4 



Soft Iron 



0-750 

 0-500 



1250 

 10-00 



31-45 

 10-53 



7-84 

 7-83 



0-125 



0-0848 



5 

 6 



Ordinary Steel 



0750 

 0-500 



12-50 

 1000 



3160 

 10-57 



7-83 



7-81 



0125 



0-0848 



7 

 8 



Wolfram Steel 



0-750 

 0-500 



12-50 

 10-00 



31-82 

 10-53 



7-90 

 7-95 



0125 



00848 



* Nagaoka, Phil. Mag. 

 p. 487 (1894). 



-cl. xxxvii. p. 131 (1894) ; Wied. Ann. Bd. liii. 



