﻿108 Determination of the -Ratio of the Electrical Units. 



would act if 1= go . In the case above considered of b — 2a, 

 the latter is equal to about ^. 



As has been stated, the principal value o£ hi is 2*404 l/b. 

 If we suppose that the distance between C and the bottom of 

 B is equal to the diameter of the latter, i = 2b, and sinh 

 (4*808) may be identified with ^<? 4 ' S08 , while the other terms 

 corresponding to higher values of k may be neglected. 

 Hence 



Correction to force — 2e _9 ' 6 = (6500) _1 . 



This compares with J : so that if the correction be neglected 

 altogether the error would be less than 1 in 2200. This 

 error, although finally halved, is too great. It would be 

 necessary either to increase the value of / a little, or to 

 calculate the correction and allow for it. 



Perhaps the weakest point in the use of an absolute 

 electrometer on these lines is the rather high potential required 

 to attain the necessary sensitiveness. There should be no 

 difficulty over ■£$ mg., especially if the necessary changes 

 could be made without taking the moving parts of the 

 balance off their knife edges. But even then 2000 volts would 

 scarcely suffice, and it is likely that 3000 or 4000 would prove 

 necessary*. 



The objection to a high potential is not so much the difficulty 

 of obtaining it with steadiness as the risk of a brush-like 

 discharge through the air, the occurrence of which would 

 probably be fatal to the success of the measurements. In 

 order to diminish the risk, the edges of the cylinders A, B, C 

 should be rounded off, as can be done without theoretical 

 objection. 



I scarcely know whether the necessity of measuring a high 

 potential in electromagnetic measure (say in volts) is to be 

 regarded as a disadvantage in this method of determining v. 

 It would seem that such measurements are needed in any 

 case and that they constitute a separate problem. 



Upon the whole, while still disposed to give the preference 

 to the condenser, I am of opinion that the electrometer 

 method is worthy of further trial. 



Terliug Place, Witham, June 1906. 



* Humiuzescu employed about 2000 volts. 



