190 



ELECTROMETRY. 



Suppose, for instance, that we have V = 800 volts, V l = 0, and 

 and V 2 = 40 volts. The ratio of the deflections and - 6', corre- 

 sponding to the two values of the potential, is then 







-0' 



_2_ = 78o = 39 

 V 820 41 



Fig. 154- 



The difference of the deflection is 0-05, and the potential of air 

 is often much higher than 40 volts. It may even happen that the 

 two deflections are on the same side ; in that case V 2 >2V. 



819. We may materially simplify the construction of this electro- 

 meter, without detracting from its sensitiveness and its accuracy. 

 The Leyden jar and its accessories replenisher, gauge, etc. are 

 dispensed with. The apparatus, reduced to quadrants, and the 

 needle are contained in a metal case (Fig. 154), on the cover of 



