72 Messrs. K. Honda and T. Terada on the 



effective field, all expressed in c.G.s. units ; T denotes the 

 tension in grams per square millimetre, and r the twist in 

 minutes of arc per unit of length. 



I. Swedish Iron and Tungsten-Steel. 



The effect * of tension or of torsion on the magnetization 

 of iron and steel is so well known that it is superfluous to 

 enter into a detailed description of the effect. Only the 

 general features of the change of magnetization will be given 

 here. It will, however, be noticed that our investigation has 

 one characteristic, that several effects of the stress on 

 magnetization were studied on the same specimen with 

 special attention to the order of applying the stress and the 

 field. The specimens were also those on which strains caused 

 by magnetization had been fully studied ; hence the numerical 

 results of the present experiment should be of some use 

 to theoreticians, who have either already obtained, or may 

 attempt to obtain, some reciprocal relations between mag- 

 netization and stress, so that they will be given in their 

 proper places. 



(a) Change of Magnetization by Tension under Constant 

 Field: (SI,T) H . 



As will be seen from figs. 1 & 3 (PL I.), the change of mag- 

 netization SI; due to the initial effect o£ loading increases up 

 to a moderate field, and then decreases with it. In Swedish 

 iron, curves (SI;, T) H in weak fields initially bend upward, 

 and after passing through an inflexion-point, the curvature 

 changes sign. As the field is increased, the point of inflexion 

 approaches the origin ; in strong fields, SI; is very small, and 

 the curve is nearly straight. In tungsten-steel, curve 

 (SI;, T)n has a slight curvature for all fields. 



In weak fields, the effect of removing the suspended weight 

 is very small and slightly increases the magnetization. 

 Subsequent loading causes an increase of magnetization ; 

 and unloading, a decrease. In strong fields, the initial and 

 the cyclic effect of loading nearly coincide with each other. 

 Curves (SI C , T)n for cyclic effects are given in figs. 2 and 4 

 in magnified scale. Curves (SI;, H) T as deduced from the 

 initial effect of (SI;, T) n are given in full lines in figs. 5, 6 

 and 7 ; they rise and then fall steeply in low field, and after- 

 ward decrease slowly, cutting the axis of H at the Villari 



* See Wiedemann's Electricitat, iii. chap. 4 ; E wing's ' Magnetic 

 Induction/ chap. 9 ; Winkelmann, Handbuch der Physik, Zweite Auflage, 

 V. 1? pp. 301-307, 313-319. 



