QUADRANT ELECTROMETER. 



Variations of temperature have a marked influence on the indi- 

 cations of the gauge, from the changes which they produce in the 

 elasticity of the wire. 



X810. QUADRANT ELECTROMETER. The quadrant electrometer 

 does not lend itself so well as that just described to absolute 

 measurements, but its manipulation is more convenient, and it may 

 be rendered far more sensitive ; it is especially used for comparing 

 potentials. 



The calculation made for the case of three concentric cylin- 

 ders (98) represents with sufficient exactitude the theory of the 

 quadrant electrometer. 



The two fixed cylinders A and B of the theoretical figure are 

 replaced by two pairs of quadrants A A' and BB' (Fig. 153), which 



Fig- 153- 



represents a flat cylindrical box, divided into four equal parts by two 

 sections at right angles, passing through the axis. Each of these 

 quadrants has at the top a circular groove. Two opposite quadrants 

 are in electrical connection. 



The cylinder C is replaced by a very light needle placed in the 

 centre of the box, and movable about a vertical axis. This needle, 

 which is cut out of thin sheet aluminum, may have any given sym- 

 metrical shape ; but in order to agree as closely as possible with 

 theory, and obtain the most uniform results, it reduces to two 

 circular plates of 90, attached at the centre by two narrow bands, 

 which are represented by the extreme radii. 



This needle has a bifilar suspension,* arranged so that, all the 

 parts being neutral, the system is in equilibrium when the needle is 



* A metal wire may also be used, or a single silk fibre may be used, with a 

 small magnet. 



