300 



YOSHIJIRO KATO : 



The magnetometer stands magnetically east of the iron wire, and 

 receives light from a slit placed 1 metre off, the image of which it reflects 

 upon a millimeter scale just above the slit. The arrangement is so 

 made that when the image is just over the slit, the magnetometer is 

 free from any deflecting force. 



The distance of the magnetometer from the nearest pole of the 

 iron wire is 5.9 cm. The intensity of magnetisation per 1 mm. of 

 the scale is .119 C. G. S. 



Method of Observation. 



The wire to be tested was heated to redness in a porcelain tube 

 and was w T ell annealed. It was then carefully taken out of the tube 

 and was hung inside the solenoid. By subjecting it to the 

 process of demagnetisation by reversals, any trace of magne- 

 tisation could be taken away. The next process was to determine a 

 proper position for the compensating coil, C, so as to cancel the 

 immediate effect of the magnetisation of the wire on the magnetometer. 

 A certain position being given to the coil, a current was instan- 

 taneously sent by the contact maker, T. If there were any sudden 

 deflection of the image, the coil was moved towards or away from 

 the magnetometer in such a way as to cancel as much as possible the 

 initial sudden deflection. This process was repeated, if necessary, until 

 a position was determined for the coil, such that, on passing the 

 current, there was no apparent sudden deflection of the image, but a 

 sIoav and continuous motion of it along the scale. Then i the wire 

 Was once more demagnetised by reversals and the current was suddenly 

 made. The position of the image, as it slowly crept along the scale, 

 was read by eye-and-ear method at various instants after " make." 



