Electric Residue in the Ley den Jar. 415 



titles of electricity in these bottles b and e, at equal tensions on 

 their knobs, had the proportion 508 : 1303. 



To both jars a charge was momentarily imparted, which was 

 immediately indicated by the sine-electrometer as 1'4941 ; and 

 on discharging the jars after an interval of 9 minutes, the 

 residues 0-3052 and O'llSO were collected. 



The proportion of the mean densities of electricity in the two 

 bottles b and e, if they possess equal tensions at their knobs, is 



508 1303 , ^^„ 

 275=^30'"^"^ = ^'^^- 



The proportion of the quantities of electricity concealed as 

 residues in b and e is 



508 X 0-3052 : 1303 x 0-1180, or 1 : 0-991. 



We see, therefore, that the jar, whieh, compared with a second, 

 has three times the thickness of glass, produces the same quantity 

 of electricity as residue, although the mean density is three times 

 less. 



Exactly similar phsenomena were observed with two Franklin's 

 plates of unequal thicknesses. 



§9. 



For a moment let us subject the usual explanation of the 

 electric residue to a stricter examination. 



According to it, the pressure of the electricity imparted to the 

 one coating, and the strong attraction of the opposite electricity 

 on the other coating, gradually force a part of the same into the 

 glass. Either the whole of the electricity which thus penetrates 

 the glass, or only the part which lies deepest, is prevented from 

 sharing in the discharge, and gradually makes its appearance 

 afterwards; for although the mutual attraction between the 

 electricities in the glass has not ceased, the reappearance of the 

 same may be accounted for, without attributing a repulsive force 

 to the substance of the glass, by the changed conditions of equi- 

 librium after the discharge, and particularly by the cessation of 

 the pressure of the imparted electricity on the corresponding 

 coating. 



This explanation, however, necessarily involves the assump- 

 tion, that the potential of the electricity which remains in the 

 glass after discharging is zero for every point within the insu- 

 lated coating. This results from the following conclusions : — 



Let us suppose the insulated coating to have received a posi- 

 tive charge : then, according to hypothesis, there will be a stra- 

 tum of positive electricity in the glass under it, and a stratum of 

 negative electricity on the other side. The whole or a part of 



