i 88 Curved dielectric plates not different from flat 



The lengths of the coating here set down are the real lengths. But in 

 computing the charges of the white jar and cylinder and the three green 

 cylinders, these lengths were increased on account of the spreading of 

 the electricity according to the same supposition as was used in computing 

 the charges of the flat plates. 



But in computing the charges of the thermometer tubes no correction 

 was made, as I was uncertain how much to allow, but as the length of 

 their coatings is so great, this can hardly make any sensible error. 



384] It should seem from these experiments as if the proportion of 

 the real to the computed charge was rather less in a cylinder in which 

 the thickness of the glass is \ of the semidiameter than in one in which 

 it is only ^, and most likely rather less in that than in a flat plate, but 

 then it seems to be not much less in a cylinder in which the inside diameter 

 is many times less than the outside, that is, in which the thickness of the 

 glass is almost equal to the outside semidiameter, than it is in the first 

 mentioned cylinder. 



Nothing certain, however, can be inferred as to this point, as in all 

 probability the four pieces of flint glass used in these experiments and 

 the two flat pieces used in [Art. 370] did not consist exactly of the same 

 kind of glass, as indeed appears from their specific gravities. 



385] The three green cylinders, indeed, were all made at the same 

 time and out of the same pot, so that it seems difficult to suppose that 

 there should be any difference of that kind between them*. But then I 

 had no flat plates to compare them with. 



On the whole, I think we may with tolerable certainty infer that the 

 ratio of the real to the computed charge is not very different from what 

 it is in flat plates, whatever is the proportion which the thickness of the 

 glass bears to the diameter of the cylinder, though it seems to be not 

 exactly the same. 



* Though it seems not likely that there should be any difference in the nature 

 of the glass of which the three green cylinders consisted, yet I am not sure that 

 there was not, for the inside of the glass, that is, that part which was nearest to the 

 inside surface, was manifestly more opaque and of a different colour from the 

 outside, and the separation between these two sorts of glass appeared well defined, 

 so that the cylinder seemed to consist of two different coats of glass lying one over 

 the other. The distinction was the most visible in those cylinders which consisted 

 of the thickest glass and in the thickest part of those cylinders. The specific 

 gravities, however, do not indicate any difference in the nature of the glass. What 

 was the reason of the above-mentioned appearance I cannot tell. 



