CHANGE OF VOLUME AND OF LENGTH. 61 



Change of Length. 



4. 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 maximnm, being longer 

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

 in length and becomes shorter than in the unmagnetized 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, wehere the contraction 

 amounts to about îoôoôô* '^^^^ present result agrees qualitatively 

 w^ith Bidwell's experiment, but the contraction is much greater. 

 The discrepancy is perhaps to be chiefly accounted for by the 

 difference of shape. 



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

 difference being the smallness of elongation and contraction, while 

 the field at which the elongation vanishes lies in the stronger. 

 The field of maximum elongation in wolfram steel is greater 

 than in ordinary steel or iron, that of no-elongation in the unan- 

 nealed state being several times greater than in iron or ordinary 

 steel. Such a field lies in H=1200. When the wolfram steel 

 is annealed, the retraction after reaching the maximum takes 

 place very slowly and the characteristic as regards the field of 

 no elongation becomes exceedingly pronounced. From the curve 

 of length change, it does not appear that it will ever cut the 

 line of no-elongation even in intense fields. 



6. The curve of elongation (in dots) plotted against the in- 

 tensity of magnetization is given in Fig. 1. The change of length 



