1 48 Theory for three parallel disks 



in the middle plate should be such that the repulsion of AB and ab together 

 on the column cf shall be equal to that of the plate eg thereon in the 

 contrary direction, and the redundant fluid in each of the outer plates is 

 not much more than one-half of that which it would receive by the same 

 degree of electrification if placed by itself. Now it will appear by com- 

 puting, according to the principles delivered in Prop. XXX [Art. 141], 

 that the quantity of redundant fluid in the middle plate will be so ex- 

 cessively different according to the different manner in which the fluid is 

 disposed in the plates that there is no forming any tolerable guess how 

 much it ought to be; but if we suppose that part of the redundant fluid 

 in each plate is spread uniformly and the rest collected in the circum- 

 ference, and that in the outer plates the part that is spread uniformly is 

 ^ of the whole, as we supposed in Experiment V, the quantity of re- 

 dundant fluid in the middle plate when the distance of the outer plates 

 is 1-15 inches will not agree with observation, unless we suppose that not 

 more than the 2ist part of it is spread uniformly; but if we suppose that 

 f of the redundant fluid in the outer plates is spread uniformly the quantity 

 in the middle plate will agree with observation, if we suppose that about 

 J of it is spread uniformly and the rest collected in the circumference. 



When the distance of the outer plates is 1-65 inches there is no need 

 of supposing so great a proportion of the fluid in the middle plate to be 

 disposed in the circumference in order to reconcile the theory with obser- 

 vation. 



N.B. The more uniformly we suppose the fluid to be spread in the 

 outer plates and the less so in the middle, the greater should be the 

 quantity in the middle plate. 



The above computations were made on the supposition that the plates 

 were circles of 14 inches diameter, that is, nearly of the same area that 

 they actually were of. 



290] It will appear by just the same method of reasoning that was 

 used in the remarks on the 22nd Proposition [Art. 74], that a vastly 

 greater proportion of the redundant fluid in the middle plate will be 

 collected near its circumference than would be if the outer plates were 

 taken away, and perhaps this circumstance may make the fluid in the 

 outer plates be spread more uniformly than it would otherwise be, so 

 that it seems not improbable that the fluid in the plates may be disposed 

 in such manner as to make the experiment agree with the theory. 



The circumstance of its being necessary to suppose a greater proportion 

 of fluid in the middle plate to be lodged in the circumference when the 

 plates are at the smaller distance from each other than when they are at 

 the greater agrees very well with the theory, for it is plain that the nearer 

 the outer plates are to each other the greater proportion of the fluid in 

 the middle plate should be lodged in the circumference. 



