Effect of Stress on Magnetization. 71 



reversals, loaded with the empty pan only. A series of 

 successively increasing fields was applied step by step, and 

 the throw of the galvanometer corresponding to each incre- 

 ment of the field was recorded. Demagnetization was again 

 effected, after the specimen had been loaded with an 

 additional tension, and the magnetization tested in the same 

 way : and so on. In this way, the magnetization nnder 

 different constant tensions was obtained. 



The procedure in the experiments on the effect of torsion 

 was similar. The torsion was increased step by step nnder a 

 constant field, and the change of magnetization corresponding 

 to each step was observed. The effect of cyclic twist was 

 also investigated. The effect of the maximum twist applied 

 at once does not differ from the sum of the deflexions obtained 

 by graduated application of twists, as in the case of tension. 

 The magnetization under constant torsions was next measured. 

 These sets of experiments were repeated for several tensions 

 nearly equal to those used in our previous experiments on 

 the change of rigidity by magnetization. 



The standardization of the ballistic galvanometer was made 

 for each set of observations, though the constant remained 

 fairly uniform daring the whole investigation. Instead of 

 using each time the special coil made for the standardization, 

 we often used the compensating secondary coil for a set of 

 experiments, recording the deflexions of the galvanometer 

 corresponding to a series of magnetizing currents, and at the 

 end of a set, the induction of this coil was compared with that 

 of the standardizing coil. In this way, time and labour were 

 economized, without the risk of introclucing any sensible error 

 in the estimation of the constant of the galvanometer. 



§ 3. Kesults of Experiments. 



The intensity of magnetization was calculated in the usual 

 manner from the throw of the ballistic galvanometer with a 

 known constant, the numbers of turns of the secondary and 

 the standardizing coil, and the sections of the specimen wire 

 and the standardizing coil. The necessary correction for the 

 reduction to tangent was made for considerable deflexions. 

 The magnetizing field was calculated from the reading of 

 the ammeter of known constant combined with the known 

 number of turns of the coil. The demagnetizing force, 

 though it was very small, was also taken into account. 

 Tensions were all reduced to weights per square millimetre, 

 and torsions to twists per unit length. 



In the following pages, I denotes the intensity of magneti- 

 zation, H' the external field applied and H the internal or 



