Capacity as ajfected by floor and walls of the room 1 7 1 



By trying the charge of all four rosin plates together by the machine, 

 Fig. 20, both when placed close together and at as great a distance from 

 each other as I could, I found their charge when close together to be to 

 their charge when placed at a distance nearly as 41 to 41^, and, from some 

 other experiments I made, I am inclined to think that the charge of each 

 of the wires which connected the upper coatings of the plates was to that 

 of one plate alone as 28 to 930*. 



From these circumstances, I am inclined to think that the charge of 

 two plates together is to that of one plate alone as 21-96 to 10-34, an d 

 that the charge of the four plates together is to that of one alone as 

 42-06 to 10-34, an( i consequently that the charges of the tin circles of 

 9-3 inches, i8 inches and 36 inches are to each other as 9-3, 20-19 and 

 4375 1- 



338] Though I do not know how to calculate how much the charge 

 of the circles ought to be increased by the attraction of the undercharged 

 ground, yet I think there can be little doubt but that if the charge of the 

 plate of i8J inches is increased in any ratio whatever as that of xto x i8|, 

 the charge of the plate of 36 inches will be increased in the ratio of x to 

 x 36, and that of the plate of 9-3 inches in the ratio of x to x 9-3 ; 

 therefore if we suppose that the charge of the i8J inch plate is increased 

 in the ratio of 9 to 8, or of i66 to i66J i8i, the charges of the three 

 plates should be to each other as 



36 x i66| i8 x i66J , 9-3 x i66 



, - and ' 



130^ 148 I57'2 



that is, as 43-37, 19-65 and 9-3, 



which agrees very nearly with experiment, and nearer so than it would 

 have done if we had supposed the charge of the i8 inch plate to have 

 been increased in any other proportion which can be expressed in small 

 numbers J. 



339] I think we may conclude therefore that the charge of the 12-1 inch 

 globe was increased by the attraction of the undercharged ground nearly 

 in the proportion of 9 to 8, for I think there can be little doubt but that 

 the charge of the globe must be increased thereby in nearly the same 

 ratio as that of the i8 inch plate, and therefore we may conclude that the 

 charge of the plate D is to the charge which the 12-1 inch globe would 

 receive, if it was placed at a great distance from any over or undercharged 

 matter, nearly in the proportion of 26-3 to 12-1, or, in other words, the 

 charge of the plate D is 26-3, which is rather more than eight times greater 

 than it ought to be if the electric fluid did not penetrate into the glass. 

 I shall speak further as to the cause of this in [Art. 349]. 



* [Arts. 555, 558, also 443.] t [Art. 649.] 



J [Art. 652, and Note 24.] 



