514 A. M. Mayer — A large Spring-balance Electrometer. 



nine light and straight rye straws. Six of these formed chords 

 of 60°, the other three formed an equilateral triangle included 

 by the hexagon. This prevents flexure of the plate when it 

 is suspended at three points by the fine wires shown in the 

 figure. This silvered disc is surrounded by a guard-ring sup- 

 ported on three paraffined glass rods. The ring and rods are 

 not shown in the figure. 



Under the silvered disc and parallel to it is a brass plate con- 

 nected with the earth, and moveable up and down by means of 

 a rack and pinion and a micrometer-screw. In ordinary work 



before a class the micrometer-screw is not required. The dif- 

 ference between the distances of the earth-plate from the mica- 

 disc is only required in the measurement of specific inductive 

 capacity, and this difference can be measured accurately enough 

 by means of a millimeter scale cut on the column of the sup- 

 port of the earth-plate. 



A tube of thin glass is cemented at the center of the top of 

 the mica disc. On this tube is pasted a piece of paper with a 

 fine line drawn on it parallel to the disc. Through the tele- 

 scope on the right we sight on a horizontal thread this line,. 



