286 Professors Ayrton and Perry on the Ratio of the 



or with, the other. The fork F turning on the pivot P con- 

 sisted of two arms perfectly insulated from one another ; the 

 one/x connected with the point A of the resistance-coils, the 

 other arm / 2 , which consisted of a piece of Atlantic-cable core 

 with pointed paraffined ends (to prevent any surface leakage) 

 was connected with one terminal of the galvanometer. The 

 stiff wire w rigidly attached to the lower plate L of the con- 

 denser and passing through a hole in the bottom of the brass 

 box bbbb without touching it, could therefore, by turning the 

 fork* F, either (1) be connected with the pole A of the battery, 

 or (2) left insulated, or (3) discharged through the galvano- 

 meter. Both surfaces of contact were platinized. (The same 

 set of connexions might have been arranged with an ordinary 

 " charge and discharge key," but with not such perfect ab- 

 sence of leakage ; for the lever of such a key which is sup- 

 ported on ebonite pillars, and along which some surface leak- 

 age must have taken place, would have had to be connected 

 with the wire iu.) The box bbbb and the other pole of the 

 galvanometer were permanently connected with A, which was 

 joined to earth. 



A complete experiment was as follows : — 



1. yi pressed against w and K pressed down, so that U was 

 connected with B. 



2. f x removed from w and then K liberated, so that U was 

 discharged. 



3. / 2 pressed against w, so that L was discharged through 

 the unshunted galvanometer, producing a deflection c? 2 . 



The rationale of the process will easily be seen. By making 

 L part of the brass box while charging, we are independent of 

 the action of its edge and of the shape of the curved ribs on its 

 lower surface (see figs. 1 and 3) ; and by connecting U with 

 the box before discharging L we obtain a complete discharge 

 from the latter. 



The experiment was occasionally varied by leaving L insu- 

 lated for some time after putting U to earth; and the apparatus 

 was not considered in good order if any perceptible diminution 

 from leakage was observed in the discharge of L to result from 

 an insulation of several seconds. 



Let C be the current, in absolute electromagnetic units 

 (gramme, centimetre, second), which flows in the first case 

 through the galvanometer. 



Let a x be the angular deflection produced, 



g the resistance in absolute units of the galvanometer, 

 s „ „ „ „ shunt, 



E the resistance in absolute units introduced into the 

 circuit, 



