288 ELECTROSTATICS. [PT. II. CH. VI. 



In Lord Kelvin's form of the quadrant electrometer, a re- 

 plenisher is used to bring V 3 , the potential of the needle, to a 

 definite value, which is controlled by a small guard-ring attracted 

 disc electrometer, called the gauge. Descriptions of the complete 

 instrument are found in Lord Kelvin's Reprint of Papers on Electro- 

 statics and Magnetism, and in the usual treatises on Electrical 

 Measurements. 



