PARAMAGNETIC & DIAMAGNETIC SUBSTANCES 289 



omitted. The force for a given deflection was obviously deter- 

 minate from the moment of inertia and the time of vibration. 



The body was contained in a small bulb. When the effect of 

 temperature was to be investigated the bulb could be surrounded 

 by a jacket electrically heated, as represented diagrammatically in 

 Fig. 220, the heating coil being surrounded by porcelain. Outside 



^ T 



FlG. 220. 



" bulb containing the body, <T porcelain rod, TTT metal tube from 



end of torsion rod, PP porcelain electrically heated oven, c thermo 



junction, ABC water jacket, EE case. 



this was a screen through which water circulated. Below, the 

 apparatus was boxed in by wood to lessen convection currents. 



To correct for the action on the bulb and the supporting rod 

 the force was measured on the bulb when containing the body and 

 again when it was empty. To correct for the air displaced by the 

 body it was assumed that the value of ^ for nitrogen is negligible, 

 so that its value for air is due to the oxygen. To determine 

 X for oxygen the bulb was filled with oxygen at a known con- 

 siderable pressure, and the force was measured. Then the point of 

 the bulb was opened and oxygen escaped till the pressure was that 

 of the atmosphere. The force was again measured, and the 

 difference gave the force upon the oxygen which had escaped if 

 that amount occupied the volume of the bulb. 



