Penetration of glass by charge 101 



the glass or move within it, and that the thickness of the glass was equal only 

 to the sum of the thicknesses of those spaces in which the fluid is immoveable. 



172] COR. II. Whether the electric fluid penetrates into the glass or not, it 

 is evident that the quantity of redundant fluid on one side the glass, and of 

 deficient fluid on the other, will be very nearly the same, whether the coatings 

 are thick or thin. 



173] PROP. XXXVII. It was shewn in the remarks on Prop. XXII in the 

 first Part, that when the plate of glass is flat, and the fluid within it is im- 

 moveable, the attraction of the deficient fluid in DF makes the redundant fluid 

 in A B to be disposed more uniformly than it would otherwise be. Now if we 

 suppose the fluid within the glass to be moveable as in the preceding proposition, 

 and that the deficient fluid in the planes Pp, Ss, &c. and the redundant fluid 

 in the planes Rr, Tt, &c. is equal to, and disposed similarly to that in DF, the 

 redundant fluid in AB will be disposed more uniformly than it would be if the 

 fluid within the glass was immoveable, and its thickness no greater than the 

 sum of the thicknesses of those spaces in which the fluid is immoveable. 



For let the intermediate spaces be moved so that Tt shall coincide with Vv 

 and Rr with Ss, &c., but let the distance between Tt and Ss and between Rr 

 and Pp, &c. remain the same as before, that is, let the thickness of the spaces 

 in which the fluid is moveable remain unaltered. The distance of Pp from Nn 

 will now be equal to the sum of the thicknesses of the spaces TtVv, RrSs, NnPp, 

 &c. in which the fluid is immoveable. 



Now, after this removal, the effect of the planes Tt and DF and of Rr and 

 Ss, &c. will destroy each other, so that the intermediate spaces and DF together 

 will have just the same effect in rendering the redundant fluid in AB more 

 uniform than the plane Pp alone will have, that is, the fluid in AB will be 

 disposed in just the same manner as if the thickness of the glass was no greater 

 than the sum of the thicknesses of the spaces in which the fluid is immoveable, 

 and the whole fluid within the glass was immoveable. 



But the effect of the intermediate spaces in making the fluid in AB more 

 uniform was greater before their removal than after, for the effect of the two 

 planes Pp and Rr together, and also that of Ss and Tt together, &c. is the 

 greater the nearer they are to AB. 



174] COR. The redundant and deficient fluid in the intermediate spaces will 

 in reality be not exactly equal and similarly disposed to that in DF, and in all 

 probability the quantity of deficient fluid disposed near the extremity of DF 

 will be greater than that in the corresponding parts of Pp, Ss, &c., or than the 

 redundant fluid in the corresponding parts of Rr, Tt, &c., so that the redundant 

 fluid in AB will perhaps be disposed rather less uniformly than it would be if 

 the deficient and redundant fluid in those spaces was equal to and similarly 

 disposed to that in DF; but on the whole there seems no reason to think that 

 it will be much less, if at all less, uniformly disposed than it would be if the thick- 

 ness of the glass was equal to the sum of the thicknesses of the spaces in which 

 the fluid is immoveable, and the whole fluid within the glass was immoveable. 



