438 



Mr. R, Shida. 



Wire " and " Glass-hard Steel Wire." Referring to the Diagram I, the 

 curves (a) and (b) are those corresponding to the cases "On" and 

 " Off " respectively directly after operating " Ons and Offs" while the 

 magnetising force was acting ; the curve (c) is one showing the effect 

 of suddenly reversing the current in the coil ; the curves (d) and (e) 

 are those showing the effect of " Ons and Offs" while the reversed 

 current was circulating through the coil, the former corresponding to 

 the case " On " and the latter to " Off " ; while the curve (/) is one so 

 drawn that the ordinate at every point of it is half the algebraical 

 difference of the ordinates of the curves (b) and (c), and hence 

 exhibits approximately a curve which should have been obtained 

 had the wire been experimented on without being subjected to 

 the action of a pnll. Had it not been for the sake of convenience 

 of comparison, therefore, the curves (c), (d), and (e) should have been 

 drawn on the negative side of the origin. Exactly the same explana- 

 tion applies to the curves in the Diagram II as to the corresponding 

 curves in the Diagram I. 



In the Diagram III, the curves (a) and (b) show the results for 

 " Steel Pianoforte Wire," and are subject to the same explanation as 

 the corresponding curves (a) and (6) in the Diagram I or II ; while 

 the curves (c) and (d) refer to the " Glass-hard-tempered Wire " the 

 former representing the result obtained when the magnetising force 

 was in action, and the latter that obtained immediately after it was 

 withdrawn. 



Glancing at the curves in the Diagram I, we see something very 

 striking. In the first place, we cannot help being struck with the 

 remarkable effect of "Ons and Offs " on the magnetisation of the 

 dark wire, when we compare the curve (a) or (b) with the curve (/). 

 But a still more remarkable result is revealed in the fact that there is 

 a surprising difference, as the curves (a) and (b) show, between the 

 intensity of magnetisation of this wire in the case of " On," and that 

 in the case of " Off " for low magnetising forces ; and that the differ- 

 ence gets less and less remarkable as the magnetising force is more 

 and more increased, becoming nothing at 15 units of the force, then 

 changing into a negative quantity for still higher magnetising forces, 

 and ultimately attaining a constant negative value. In other words, 

 the intensity of magnetisation of the wire is greater or less while it is 

 actually under the action of a constant pull than while it is free from 

 it, according as the magnetising force to which the wire is subjected 

 is below or above a certain value — a value which might, therefore, be 

 called critical* The fact that the two pairs of curves (d) and (e) 



* This confirms the result given on page 62 of Sir William Thomson's paper on 

 the " Eleetrodynamic Qualities of Metals, Part YII" ("Phil. Trans.," 1879), in 

 ■which he calls this value " Yillari Critical "Value," as having been previously 

 obtained by Yillari. 



