82 Messrs. K. Honda and T. Terada on the Change of 



Thus the change of the coefficient of thermal expansion by 

 magnetization is equal to the temperature coefficient of the 

 magnetic elongation. As the latter coefficient is known from 

 the experiment * by Mr. S. Shimizu and one of us, the values 

 of 8a are calculated and graphically drawn in PI .V. figs. 51, 

 52, 53, 54, and 55. 



By referring to the figures, we see that the change of the 

 coefficients of thermal expansion by magnetization depends 

 considerably upon temperature. Ordinates of the curves 

 represent the change of the mean coefficient of expansion 

 between two temperatures belonging to each curve. 



The change of the mean coefficient of expansion in nickel 

 (fig. 51) between the ordinary and liquid air temperatures 

 first decreases, attains a minimum, and then gradually 

 increases, as the field becomes greater, till it is greater than 

 its initial value. At a temperature higher than the ordinary, 

 the change of the coefficient of expansion steadity increases, 

 soon approaching an asymptotic value. In a given field, its 

 value increases with temperature, and after passing through 

 a maximum, slightly decreases. The maximum amount of 

 the change is of the order of 1 per cent, of the coefficient 

 itself. 



In soft iron and tungsten-steel (figs. 52 audi 53), the change 

 of expansion is very small. Up to a moderate temperature, 

 the cofficient of expansion increases steadily with the field, 

 except in weak fields, in which a small decrease is observed. 

 At higher temperatures, the change becomes negative for all 

 fields. In iron, a maximum decrease is observed. 



In cast cobalt (fig. 54), the change of the coefficient of 

 expansion at low temperature increases with the field, reaches 

 a maximum, and then decreases. As the temperature becomes 

 higher, the amount of the maximum gradually lessens ; -the 

 position of the maximum shifts towards lower fields and the 

 curve at last cuts the zero line. At a sufficiently high tem- 

 perature, the change of expansion is always negative. 



The change of the coefficient of expansion in annealed 

 cobalt (fig. 55) is rather abnormal, and its maximum amount 

 is relatively large, being about 2 per cent. The change of 

 the mean coefficient of expansion between the ordinary and 

 liquid air temperatures steadily decreases with the field, 

 though its amount is small. As the temperature rises, the 

 amount of the diminution increases rapidly and then decreases. 

 Here the course of the curve shows a minimum decrease of 



* K. Honda and S. Shimizu, Jour. Sc. Coll. xx. Art 30, 1903. 



