174 No specific effect of plates of air 



I could not perceive any sensible difference in the charge, whether I 

 lifted up the upper plate in the above-mentioned manner, or whether 

 I tried its charge without lifting it up. 



345] It is plain that in lifting up the upper plate from the lower and 

 letting it down again, the greatest part of the air contained between the 

 two plates must be dissipated and mixed with the other air of the room, 

 so that if the air contained between the two plates was overcharged on 

 one side and undercharged on the other, the charge must have been very 

 much diminished by lifting up the upper plate and letting it down again, 

 whereas, as I said before, it was not sensibly diminished. 



I think we may conclude, therefore, that redundant and deficient fluid 

 is lodged only in the plates, and that the air between them serves only 

 to prevent the electricity from running from one plate to the other. 



346] As this is the case, the charge of these plates ought, according 

 to the theory, to be equal to that of a globe whose diameter equals the 

 square of the radius of the plate or circular coating divided by twice their 

 distance, that is, to their computed charge, provided the electricity is 

 spread uniformly on the surface of the plates, and therefore in reality 

 the numbers in the last column but one ought to be rather greater than 

 in the last but two, and moreover the less the distance of the plates is in 

 proportion to the diameter of the coating, the less should be the proportion 

 in which those numbers differed, and if the distance is infinitely small in 

 proportion to the diameter, the proportion in which those numbers differ, 

 should also be infinitely small. 



347] This will appear by inspecting the table to be the case, only it 

 seems from the manner in which the numbers decrease, that they would 

 never become equal to unity though the distance of the plates was ever 

 so small in respect of their diameter, and I should think, or rather I 

 imagine, would never be less than i-i, so that it seems as if the charge 

 of a plate of air was rather greater in proportion to that of the globe than 

 it ought to be, and I believe nearly in the proportion of n to 10*. 



348] The reason of this, I imagine, is as follows. It seems reasonable 

 to conclude from the theory that when a globe or any other shaped body 

 is connected by a wire to a charged Leyden vial, and thereby electrified, 

 the quantity of redundant fluid in the globe will bear a less proportion 

 to that on the positive side of the jar than it would do if they could be 

 connected by a canal of incompressible fluid f, but in all probability when 

 a plate of air is connected in like manner to the Leyden vial, the quantity 

 of redundant fluid on its positive side will bear nearly the same proportion 

 to that in the vial that it would do if they were connected by a canal of 



* [Art. 670.] 



f This seems likely from Appendix, Coroll. V [Art. 184]. 



