Influence of variation of the arrangements 139 



The plate was tried in some of these situations another night, when 

 the charges came out in the following proportions * : 



2nd Way. . . . 11-9, 



3rd . . . . 12-0, 



5th .'-. . n-8, 



6th . ii-o. 



268] It should seem from these experiments that the charge of the 

 tin plate is not exactly the same in all the ways of trying it, as the extremes 

 seem to differ from each other by above T ' 5 part, which is more than could 

 arise from the error of the experiments; but, excepting the 4th and 6th 

 ways, the others seem to differ by less than ^. This I think we may be 

 well assured of, that no sensible error can arise in the following experi- 

 ments from any small difference in the manner in which the bodies are 

 touched by the wire. 



269] EXP. IV. These experiments were made with intent to see 

 whether the charge of a body of a given shape and size was the same 

 whatever materials it consisted of, as it ought to be according to Prop. 

 XVIII f, and also to see how far the charge of a flat plate depended on 

 its thickness J. The substances used for this purpose were all flat plates 

 about one foot square. The results of the experiments are given in the 

 following Table : 



N.B. The three pieces of stone were all ground flat, and of an uniform 

 thickness. 



270] As it would have been difficult to try the following substances 

 by themselves, I coated panes of crown-glass with them on one side and 

 tried them in that manner, which, as glass does not conduct electricity, 



* [Art. 468.] 



J [Prop. XXI, Art. 73.] 



f [Art. 68.] 



[Arts. 293, 471, 480, 481.] 



