1882.] 



R. Shida. Magnetic Susceptibility. 



285 



II. " Experimental Determinations of Magnetic Susceptibility 

 and of Maximum Magnetisation in Absolute Measure." By 

 R. Shida, Thomson Experimental Scholar, University 

 Glasgow. Communicated by Sir William Thomson, F.R.S. 

 Received October 10, 1882. 



(Abstract.) 



This paper contains the resnlts of a series of experimental de- 

 terminations of the magnetisation, magnetic susceptibility, &c, of 

 different specimens of iron and steel, in centimetre gramme second 

 nnits, by means of the direct magnetometric method shown to me by 

 Sir William Thomson, as founded upon a method originated by Coulomb 

 and mathematically discussed by Green. 



A number of thin wires (from No. 20 to 22 B.W.G.) of soft iron 

 and steel were tried in the first elaborate series of investigations. 

 The experiments were varied by varying the strength of the mag- 

 netising force through a wide range ; and for each magnetising force, 

 and for each wire, the experiment was commenced by subjecting the 

 wire to the application and removal of a longitudinal stress a certain 

 number of times in succession (that is, "ons and offs "), while the 

 magnetisation and magnetic susceptibility of the wire were deter- 

 mined for each degree of magnetising force, and both while the wire 

 was actually under the influence of a constant pull (a case to be 

 denoted by "on "), and while it was free from a pull (a case to be 

 denoted by "off"). In the case of soft iron wires, the effects of 

 suddenly reversing the magnetising force, and of " ons and offs " after 

 the reversal of the force, were also investigated. Some interesting 

 and remarkable results followed from these experiments ; and the 

 evaluations, made from these results, of the intensity of magnetisa- 

 tion and magnetic susceptibility, are carefully tabulated, and also 

 represented graphically, for the sake of comparison, in two sets of 

 curves — one, which shows the intensity of magnetisation, that is to 

 say, in which the abscissae are proportional to the magnetising force 

 and the ordinates to the intensity of magnetisation ; and the other, 

 which shows the magnetic susceptibility, that is to say, in which the 

 abscissae and ordinates are respectively proportional to the force and 

 the susceptibility. 



The curves of the intensity of magnetisation show that the effects 

 of " ons and offs," in augmenting the magnetisation of soft iron 

 wires, are astonishingly great for low magnetising forces, and that, as 

 the latter is gradually increased, the wires seem to lose their reten- 

 tiveness gradually, so much so, in point of fact, that when the 

 magnetising force exceeds a certain value (60 c.g.s. or so) the 

 operation of " ons and offs " produces no permanent magnetisa- 



