540 K. Honda, S. Shimizu, and S. Kusakabe on Change of 



It is evident that if the ferromagnetic rod is twisted 

 through a small angle <f>, the rotating cylinder is turned 



through an angle — ; hence the angle of torsion is mag- 

 nified in the ratio E, : r. In the actual case we corrected 

 for the thickness of the thin copper wire; the ratio was 

 106 : 1 in our case. With the arrangement we were able to 

 measure a change of angle amounting only to l //r *92 X 10" 3 

 per cm. of the ferromagnetic rod. 



3. The measurement was conducted in the following 

 order: — The specimen to be tested was fixed in the axial 

 line of the magnetizing coil so as to lie nearly in a uniform 

 field. If the steel pivot on one end of the bar carrying the 

 specimen was left free, and a magnetizing current passed 

 through the coil, a deflexion of the mirror was observed, 

 though there was no twisting couple. The deflexion is 

 evidently not due to the twisting of the rod, but to its bend- 

 ing by magnetization. The case corresponds to the experi- 

 ment of Guillemin described in the preceding paper *. The 

 nature of the deflexion and its amount coincided with the 

 change of elasticity by magnetization, which we have already 

 studied. The steel pivot was then brought slightly in con- 

 tact with the agate cup ; if the contact was made in a suitable 

 degree the deflexion due to magnetization, when acted on by 

 no twisting couple, could be made negligibly small. In cases 

 when the deflexion could not be sufficiently reduced, it was 

 always corrected for. The contact being so adjusted a couple 

 was applied by a suspended weight. The tension of the fine 

 copper wire was then adjusted and the working of the appa- 

 ratus tested by adding successively weights of 1, 10, 50 

 grams to the pan. If the deflexions of the mirror were pro- 

 portional the adjustment was considered to be correct. 



To begin with, the ferromagnetic rod was demagnetized by 

 reversals, and then a current passed through the coil, taking 

 the deflexion as soon as possible. These processes were re- 

 peated with successively increasing currents. In order to get 

 rid of the minute oscillations of the mirror the thin copper 

 wire and the mirror should be protected from air-currents. 



Tbe resistance of the magnetizing coil was only 0'6 O, so 

 that the heating of the core due to current was negligibly 

 small up to the strongest current used in the present experi- 

 ment, and the creeping of the image of the scale was not at 

 all observed ; but we were careful to read the deflexion as 

 quickly as possible. 



Since the couples corresponding to 1, 10, 50 grains 

 * Supra, p. 459. 



