Results for plates of air 173 



342] In this manner I made the experiment with the plates at four 

 different distances, namely -910, -420, -288 and -256, and when I had made 

 a sufficient number of trials with the plates at each distance, I took off 

 these circular coatings and put on smaller, namely of 6-35 inches diameter, 

 and tried the experiment as before with the plates at -259 inches distance. 

 The result of the experiments is given in the following table : 



343*] 



It is plain that some allowance ought to be made in these trials for 

 the spreading of the electricity on the surface of the glass. In the above 

 table I have supposed it to spread -05 of an inch, but the effect is so small 

 that it is of very little signification whether that allowance is made or not. 



344] In my former paper [Art. 134] I expressed a doubt whether the 

 air contained between the two plates in this experiment is overcharged 

 on one side and undercharged on the other, as is the case with the plate 

 of glass in the Leyden vial, or whether the 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, but the 

 following experiment shews that the latter opinion is true. 



I placed the two brass plates on the machine (Fig. 20), and tried their 

 charge as before, except that, after having charged the plates f, I im- 

 mediately lifted up the upper plate by a silk string so as to separate it 

 two or three inches from the lower one, and let it down again in its place 

 before I found its charge by making the communication between Bb 

 and Dd and between A a and Ee. 



The way I did this was that as soon as I had let down the wire Cc 

 on A a and Bb, and thereby charged the plates, I lifted it up again half 

 way so as to take away the communication between Cc and the upper 

 plate &c., but did not lift it quite up, so as to make the communication 

 between Bb and Dd, and between A a and Ee, till after I had separated 

 the upper plate from the lower, and put it back in its place. 



* [See Arts. 669, 519.] 



f [Arts. 511, 516, Dec. 18, 26, 1772.] 



