332 Messrs. Nagabka and Honda on Change of Volume and 

 Change of Length. 



Iron (fig. 1). — The change of length experienced by soft 

 iron is too well known to need any description. The ovoid 

 elongates in weak fields till it attains a maximum, being- 

 longer by about 3 to 4 millionths of its initial length ; it then 

 decreases in length, and becomes shorter than in the unmag- 

 netized state. The contraction goes on gradually increasing, 

 and in the present experiment it does not seem to reach an 

 asymptotic value, even in fields of 2200 c.G.s. units, where 

 the contraction amounts to about 



100,000* 



The present result 

 agrees qualitatively with BidwelPs experiment, but the con- 

 traction is much greater. The discrepancy is probably to be 

 accounted for by the difference of shape. 



Steel (fig. 1). — Ordinary steel behaves just like iron, the 

 difference being the smallness of elongation and contraction, 

 and the field at which the elongation vanishes lies in the 

 stronger. The field of maximum elongation for wolfram steel 

 is greater than for ordinary steel or iron, and that of no 

 elongation in the nnannealed state is several times greater 

 than for iron or ordinary steel. Such a field corresponds to 



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H = 1200. When the wolfram steel is annealed the retraction 

 after reaching the maximum takes place very slowly, and the 



