IOO 



Preliminary Propositions 



mS or gS, is very nearly equal to g + mS gD or to (g + m) S, therefore the 



BW 

 quantity of redundant fluid in AB will be very nearly equal to , ~ , 



and will therefore be greater than if the fluid within the glass was immoveable 

 very nearly in the ratio of one to S, or will be very nearly the same as if the 

 thickness of the glass was equal to CE x S, and the fluid within it was im- 

 moveable. 



170] PROP. XXXVI. Fig. 10. Let every thing be as in the preceding pro- 

 position, except that the electric fluid is able to penetrate into the glass on the 

 side Nn as far as to the surface Kk, and on the side Vv as far as to Yy ; in such 

 manner, however, that though the fluid can move freely from A B to aft or from 



Fig. 10. 



a/3 to AB, and also from DF to &<f> or from 8<f> to DF, in a direction perpen- 

 dicular to those surfaces, yet it is unable to move sideways, or in a direction 

 parallel to those surfaces: the quantity of redundant fluid on one side of the 

 glass, and of deficient fluid on the other, will be very nearly the same as if the 

 spaces NnkK and VvyY were taken away and the coatings AB and DF were 

 applied to the surfaces Kk and Yy. 



For by [Art. 132] of former Part, almost all the redundant and deficient 

 fluid will be lodged on the surfaces a/3 and S<f>, and the coatings AB and DF 

 will be not much over or undercharged. Now if the whole of the redundant 

 and deficient fluid was lodged in a/3 and S(f>, it is evident that the quantity of 

 redundant and deficient fluid would be exactly the same as if the spaces NnkK 

 and VvyY were taken away, and therefore it will in reality be very nearly the 

 same. 



171] COR. I. Therefore the quantity of redundant fluid on the positive side 

 of the glass, that is, in the coating AB, and the space AaftB together, as well 

 as the quantity of deficient fluid on the negative side of the glass, will be very 

 nearly the same that they would be if the fluid was unable to penetrate into 



