464 K. Honda, S. Shirnizu, and S. Kusakabe on Change of 



4. Soft Iron. — In observing the deflexion from our scale- 

 reading by passing a current through the coils, we were first 

 struck with the large effect contrary to the results of previous 

 experimenters. The largest deflexions for soft iron and 

 Wolfram steel amounted to about 9 cm. with a scale at 

 2*61 m. distant in a field of 500 C.G.S. units, while for a steel 

 bar it was only one third. Even nickel, for which the distance 

 between the two fulcrums was only 22 cm., showed a deflexion 

 of 3 cm. 



The curves for the change of depression corresponding to 

 different loadings in soft iron are given in fig. 4. Ordinates 



Ffc. 4. 



-!0 cm 



/ 





















T~2\50 



// 

























V 





















T--U30 



















1/ 



If/ 























T=6'0 





















V 





















T=II0 























\{ 



10 



2( 



10 



3( 



10 



4( 



>0 



51 



>0 H 





























y. 



represent in centimetres the amount of the change of depres- 

 sion, taken positive when it indicates an increase of elasticity, 

 and taken negative when it indicates a decrease. Abscissas 

 represent the effective field, and T the suspended weight in 

 grams. 



The general course of these curves resembles that of mag- 

 netization. In weak fields, however, we notice a minute 

 decrease of elasticity when the load exceeds about 1*5 

 kilograms. Iron contracts laterally when magnetized by 

 weak currents, and this contraction may produce such an 

 apparent decrease of elasticity; but the actual calculation 

 shows that the initial depression is more than can be accounted 

 for by the lateral contraction. 



When the field increases beyond this region, the change of 

 depression increases rapidly and soon reaches its asymptotic 

 value, after which the increase takes place quite slowly. As 

 the weight is increased the change of depression is also 

 increased. The rate of increase is large with small loading 

 and decreases as the load is increased, approaching to an 

 asymptotic value. 



