Elasticity of Ferromagnetic Substances by Magnetization. 75 



(a) Measurement of ike Change of Rigidity by 

 ordinary method. 

 In a paper by Messrs. S. Shimizu, S. Kusakabe, and one 

 of us *, the change o£ rigidity o£ ferromagnetic bars is given, 

 having been determined by first applying the torsion and 

 then the magnetic field. To investigate whether the results 

 are the same or not, if the order of applying the torsion and 

 the field is reversed, the same arrangement was used as that 

 employed in the experiment above cited. The essential parts 

 of the arrangement remained unchanged, except for the 



mirror system. The rotating 

 cylinder, to which the mirror 

 was fixed, was supported 

 horizontally by means of two 

 very weak spiral springs (s s) 

 attached to the sides of a 

 carriage (c) similar to that 

 used in our measurement of 

 the change of elasticity. To 

 the carriage was rigidly 

 fixed a horizontal axis, the 

 conical ends of which fitted 

 to agate cups on the arms of 

 a Y-shaped bar (a). This 

 bar could be adjusted to any desired position, such that the 

 axis of the mirror would be pressed by the plane side of the 

 carriage perpendicularly on a point of the circumference of 

 the torsion wheel (t) rigidly fixed to the specimen. To adjust 

 the pressure properly, a sliding weight (b) was put on a pin (p) 

 protruding from the carriage. 



Two vertical scales 30 cm. long were erected at a horizontal 

 distance of 6*45 m. in front of the mirror in the same vertical 

 line ; one at the same height as the mirror, and the other 

 about one metre above it. The image of the scales was 

 observed with a telescope at the same height as the mirror. 

 An initial couple was applied and the mirror was so adjusted 

 that the image of the lower scale was observable with the 

 telescope. A suitable weight was then chosen for giving an 

 additional couple, which twisted the rod to such an extent 

 that by the cod sequent rotation of the mirror, the image of 

 the upper scale just appeared in the field of the telescope. 

 This weight was 500 gr. The readings of the two scales, 

 corresponding to the removal and to the addition of the 

 additional weight, were taken. When properly adjusted, 

 their difference was fairly constant for repeated observations; 

 the mean of several observations was always taken as the 



* K. Honda, S. Shimizu, and S. Kusakabe, loc. cit. 



