High-Fn quency Induction- Coil. 



329 



quadrant electrometer used idiostatically. Only one of the 

 quadrants was retained, and the needle was supported on a 

 horizontal axis with jewelled bearings (fig. o). These bearings 



Fiff. 3. 



were carried on glass pillars, but on account of the high 

 frequency the metallic parts had to be electrically connected 

 to the needle. Neglect of this precaution resulted in the 

 destruction of one of the jewels. The needle had suitable 

 adjustments for level and sensitiveness and carried a plane 

 mirror, enabling its deflexions to be read with mirror and 

 scale. The whole was immersed in kerosene oil, to prevent 

 sparking. The oil served also as a damper to mechanical 

 motions, and to increase the sensitiveness. The instrument 

 gave a calibration-curve which was an almost perfect parabola. 

 Its constant was frequently redetermined by the absolute 

 attracted-disk electrometer belonging to the University*. 

 * See Edmondson, Physical Heyiew, Feb. 1898. 



