Charge of condenser little affected by surroundings 103 



difference of the attractions of DF on eAf and ep. (supposing Ee and M/j. to be 

 equal to CE) very nearly as twice EC to CE, and is therefore very nearly equal 

 to twice the difference of the attraction of df and DF on EM. 



Fig. ioa. 



In like manner the attraction of the intermediate spaces on CG is very 

 nearly equal to twice the difference of the attraction of DF and df thereon. 



Suppose now the quantity of deficient fluid in DF to be increased in the 

 ratio of i + / to i, the redundant fluid in AB remaining the same as before, a 

 new attraction is produced on EM, very nearly equal to 



/ x (attraction of DF on EM) - '- x 2 (diff. attr. of df and DF on EM), 



that is, very nearly equal to/ x (attraction of df on EM). 



In like manner a new attraction is produced on CG, very nearly equal to 

 / x (attraction of df on CG), therefore, the new attraction produced on EM is 

 to that produced on CG very nearly as the attraction of df on EM is to its 

 attraction on CG, and therefore in order that the quantity of redundant fluid 

 in AB shall not be altered by the approach of N, the repulsion of N on EM 

 must be to its repulsion on CG very nearly as the attraction of df on EM to its 

 attraction on CG. 



179] PART 2. Lp t the fluid within the glass be either moveable, as in Prop. 

 [XXXV, Art. 169], or let it be immoveable, and let the distance of H and L 

 from the glass be either great or not. 



fCC (ff 



Let the repulsion of H on | ,,,.. in direction GC be | , and let the sum 



of these repulsions = S. 



(GC in direction CG = A 



Let the repulsion of ,/V on [_.,,. ,. .. ,,,,, D , and let the repulsion 



[EM in direction EM = B 



which N should exert on CG in order that the redundant fluid in AB should 

 remain unaltered be to that which it should exert on EM : : i : P. 



The quantity of redundant fluid in AB will be increased in the ratio of 

 B - PA i + p 

 S ~ P + p 

 from that of 



B- PA 



to i, which, if P differs very little from i, differs very little 



i 4- 



to i. 



