508 Sir W. Snow Harris on the Correct Interpretation 



coating) in connexion with the earth. Now we know, by very 

 familiar experiments, that, if a neutral conducting surface H, 

 fig. 6, in connexion with the earth be caused to approach a 

 charged surface — as, for example, the plane R, — an electroscope 

 r divergent to a given angle begins to subside, in consequence of 

 the total force not operating in the direction of the electrometer 

 r exclusively, but also in the direction of the approximated sur- 

 face H ; there will not in this case be the same quantity free to 

 act in the direction of the electroscope as there was before. 

 We should require therefore under this new condition an increased 

 quantity to be deposited upon the surface R before the electro- 

 scope could again diverge to the same angle. We have evidently 

 in this experiment effected no specific change in the electrical 

 agency ; we have merely caused the same or a less quantity to 

 operate on the electrometer in a given point of the surface R. 



8. Now this is precisely the condition of the electrical jar, 

 fig. 7. If we suppose the outer coating N not present, and the 

 jar insulated, a small quantity accumulated on the inner coating 

 causes a considerable divergence of the electrometer E attached 

 to the extremity of its charging-rod. Directly, however, we 

 assume the presence of the uninsulated external coating N n, the 

 influence of this upon the inner coating through the glass so 

 diverts the force acting in the direction of the electrometer E as 

 to cause its angular divergence to subside. We have here only 

 to consider, as is evident, mere force, and the direction or direc- 

 tions in which it acts, and not an occult material agency pos- 

 sessing variable hypothetical qualities of which we have no clear 

 or intelligible evidence, and the assumption of which only serves 

 to confuse and embarrass a simple idea. 



9. Let us now suppose attached to the charging-rod of the 

 jar a Lane's discharger L, the negative ball of which, directly 

 opposed to the positive ball of discharge m, is in connexion with 

 the outer coating Nw, through an external circuit omlN; then, 

 as we continue to add electricity to the inner coating, the force 

 in the direction of the discharging electrometer L begins to 

 increase, and continues to do so until discharge ensues between the 

 inner and outer coatings through the external circuit o ml N. We 

 may here consider the total force in operation to be exerted be- 

 tween the coatings in two directions ; that is to say, immediately 

 through the intervening glass of the jar on the one hand, and 

 through the external circuit o m I N on the other. 



As the amount of force through the Lane's discharger increases, 

 the force between the inner and outer coatings through the glass 

 decreases, inasmuch as the operation of the accumulation upon the 

 outer coating through an external circuit in the direction of the 

 discharging electrometer is such as to subvert the negative state 



