not influenced by strength of charge 1 77 



quently the distance through which the electricity moves in the direction 

 AE also infinitely small. 



354] Another thing which inclines me to this way of accounting for 

 it is that there seems some analogy between this and the power by which 

 a particle of light is alternately attracted and repelled many times in its 

 approach towards the surface of any refracting or reflecting medium. See 

 Mr Michell's explanation of the fits of easy reflection and transmission 

 in Priestley's Optics, page 309. 



355] To whichever of these causes it is owing that the charges of these 

 plates are so much greater than they should be if the electric fluid was 

 unable to enter into the plate, it was reasonable to expect that the greater 

 the force with which the plate was electrified, the greater should be the 

 depth to which the electric fluid penetrates into the glass, or the greater 

 should be the thickness of the spaces in which we supposed the fluid to 

 be moveable, and consequently in comparing the charge of the plate D 

 with the circle of 36 inches diameter, or with any other body, the greater 

 the force with which they are electrified the greater proportion should 

 the charge of the glass plate bear to that of the circle. 



356] I therefore compared the charge of the plate D with that of the 

 circle of 36 inches with electricity of two different degrees of strength, 

 namely the same which I made use of in [Art. 329], in trying whether 

 the distance to which the electricity spread on the surface of glass was 

 different according to the strength of the electricity. 



The way in which I compared their charges was just the same that I 

 made use of in comparing the rosin plate with the tin circles in [Art. 337]. 

 The event was that I could not perceive that the proportion which their 

 charges bore to each other with the stronger degree of electricity was 

 sensibly different from what they did with the weaker*. 



357] But it must be remembered that it seemed from the experiment 

 related in [Art. 329], that the electricity spread ^ of an inch further on 

 the surface of the glass with the stronger degree of electricity than with 

 the weaker. The difference of charge owing to this difference in the 

 spreading of the electricity is -fe part of the whole, so that it seems that 

 if the electricity had been prevented from spreading on the surface of the 

 glass, the proportion of the charge of the glass plate to that of the tin 

 circle would have been less with the stronger degree of electricity than 

 with the weaker, and that nearly in the proportion of 16 to 17. 



358] I also made an experiment to determine whether the charge of 

 a coated plate of glass bore the same proportion to that of another body 

 when the electricity was very weak as when it was of the usual strength f. 



* [Arts. 547, 551, 553, also Arts. 451, 463, 526, 535, 538, 664.] 

 t [Arts. 539, 666.] 



C. P. I. 12 



