PARAMAGNETIC & DIAMAGNETIC SUBSTANCES 287 



of an electro-magnet EEEE, Fig. 218. The figure represents the 

 horizontal plane through the magnetic axis. The torsion rod was 

 arranged so that the body could move along ox. The force upon 



JTT 2 



it was F = -g -r- v 9 where H y is the intensity, which from 

 *\ mmetry must be perpendicular to ox, K is the susceptibility, and 



v is the volume. If p is the density and 772 is the mass, we may put 



F _l * OT <*H y a 

 2 p dx 



dkl. 



w 



here \~ ~- Curie investigated the value of ^, which he 



termed " the specific coefficient of magnetisation." 



To find H y a small coil connected to a ballistic galvanometer 

 was placed at o perpendicular to H y and then turned through 180. 



