368 H. NAGAOKA AND K. HONDA; 



the accompanying figure. The coils were each 40 cm. long, wound in 

 G layers and gave the field of 17.7 C. G. S. units for a current of one 

 ampere. The magnetometer M was placed midway between the 

 solenoids, due magnetic east and west. When the current was made, 

 the magnetization of two similar bodies produced nearly the .same 

 effect on the magnetometer in the opposite sense ; thus, the deflection of 

 the magnetometer was so compensated that the magnetometer could he 

 placed very near the solenoids, and thereby rendered sensible to a 

 slight change in the condition of the magnetized body. In order to 

 make the compensation exact, the auxiliary solenoid, S', was provided 

 with levelling screws and the brass tube containing an auxiliary mag- 

 net with screw for adjusting the vertical position of the magnet. The 

 magnetizing solenoid was firmly fixed to the solid stone pier, so that 

 there was no risk of its being disturbed by the application of pressure to 

 the vessel through the bent copper tube ; it was also ascertained by 

 means of a long thread pendulum attached to the solenoid that no 

 appreciable displacement of the solenoid took place during the applica- 

 tion or removal of pressure. 



To make the reading of the magnetometer sensitive, it was 

 necessary to place the magnet in a position suitable for maximum 

 deflection ; this could be effected either by calculation for the ovoid 1} or 

 be experimentally determined for other shapes. The brass vessel was 

 moved slowly up and down to snch a position that it was not affected 

 by the small vertical displacement, thus giving the position of 

 maximum deflection. It was necessary to place the magnet in the above 

 position, owing to a slight displacement, due to the strain caused by 

 the strong pressure. For a vertical strain component, the magnetometer 

 could remain practically unaffected in the position above chosen. 



1). Xagaoka, Wied. Ann. 57, 275, (1896). 



