Estimate of accuracy 137 



cause which I am not acquainted with. For greater security I always 

 compared each body with the trial plate 6 or 7 times running. 



263] It appears from the description of the electrometer fastened to 

 the wire Pp that the vials were charged extremely weakly in these experi- 

 ments (they were indeed charged so weakly that if tried by Lane's electro- 

 meter they would not discharge themselves, if the distance of the knobs 

 was more than ^ of an inch*), and it perhaps may be asked why I chose 

 to charge them so weakly, as it is plain that the stronger the vials are 

 charged the less alteration in the size of the trial plate would it have 

 required to produce the same alteration in the separation of the pith balls. 



264] My reason was this, that the electricity seems to escape re- 

 markably faster from any body, both by running into the air and by 

 running along the surface of the non-conductor on which it is supported, 

 when the body is electrified strongly than when it is weak, which made 

 me afraid that if I had charged the vials much stronger the experiment 

 might have been too much disturbed by the diminution of the quantity 

 of redundant fluid in B and the deficience in the trial plate between the 

 lifting up of the wires Rr and Mm and letting fall the wires Dd andZ)8, 

 and also by the diminution of the charge of the vials between lifting up 

 the wire bt and lifting up the wires Rr and Mm; and indeed it seemed, 

 from some trials I made with a heavier electrometer fastened to Pp, as 

 if the experiments were not more exact, if so much so, when the vials 

 were charged stronger, as when they were charged in the usual degree. 



I now proceed to relate the experiments I have made. 



265] EXP. III. This experiment was made with a view to discover 

 whether the quantity of -redundant fluid communicated to the body B 



Fig. 17. [Scale A-] 

 * [Difference of potentials about n-8. See Art. 329 and Note 10.] 



