﻿Behaviour of the Quadrant Electrometer. 



383 



which =—7 when F = /cV 3 2 . Thus, when the potential 

 which makes the needle most sensitive is put on, while both 

 quadrants remain earthed, the needle moves into the sym- 

 metrical position. If Y 3 is less than this value it will move 

 past the symmetrical position, and if greater, not so far. If 

 the potentials of the quadrants be interchanged, V x becom- 

 ing V 2 and V 2 zero, so that the deflexion is in the opposite 

 direction, the value of is increased. The two deflexions 

 will not be equal, the greater deflexion being when the 

 needle, in its motion from rest, passes through the symme- 

 trical position. The difference of these deflexions when the 

 needle is most sensitive is equal to 27. 



The curve shown in fig. 2 gives the deflexion in milli- 

 metres of the scale when a potential of about *25 volt was 

 put on to one pair of quadrants, the other pair being earthed. 

 The potential of the needle was varied from —270 volts to 

 + 270 volts. 

























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The deflexion apparently due to 7 was made as nearly as 

 possible zero, but when it was made to vanish when V 3 was 

 positive it was found not to vanish when V 3 was negative, 

 and, in fact, it seemed to depend on the potential V 3 of the 

 needle. For instance, when V s was = —148 volts and both 

 pairs of quadrants earthed the deflexion was 2 millimetres to 



