ON ELECTRICITY IN EQUILIBRIUM. 511 



but if the length of the cylinder is considerable, the fluid within it can 

 only remain at rest when the quantities of redundant fluid are nearly equal 

 in both spheres, and consequently when the density is greater in the 

 smaller. And for a similar reason, in bodies of irregular forms, the fluid 

 is always most accumulated in the smallest parts ; and when a conducting 

 substance is pointed, the fluid becomes so dense at its extremity, as easily 

 to overcome the forces which tend to retain it in its situation. (Plate 

 XXXIX. Fig. 551.)* 



In this distribution we find a very characteristic difference between the 

 pressure of the electric fluid and the common hydrostatic pressure of 

 liquids or of simple elastic fluids; for these exert on every surface 

 similarly situated a pressure proportionate to its magnitude ; but the 

 electric fluid exerts a pressure on small and angular surfaces, greater, in 

 proportion to their magnitudes, than the pressure on larger parts : so that 

 if the electric fluid were in general confined to its situation by the pressure 

 of the atmosphere, that pressure might easily be too weak to oppose its 

 escape from any prominent points. It does not appear, however, that this 

 pressure is the only cause which prevents the escape of the electric fluid ; 

 nor is it certain that this fluid can pass through a perfect vacuum, 

 although it has not yet been proved, that a body placed in a vacuum is 

 perfectly insulated. Whatever the resistance may be, which prevents the 

 dissipation of electricity, it is always the more easily overcome, as the 

 electrified substance is more pointed, and as the point is more promi- 

 nent ; and even the presence of dust is often unfavourable to the success 

 of electrical experiments, on account of the great number of pointed termi- 

 nations which it affords. 



The general effect of electrified bodies on each other, if their bulk is 

 small in comparison with their distance, is, that they are mutually repelled 

 when in similar states of electricity, and attracted when in dissimilar states. 

 This is a consequence immediately deducible from the mutual attraction of 

 redundant matter and redundant fluid, and from the repulsion supposed to 

 exist between any two portions either of matter or of fluid, and it may 

 also easily be confirmed by experimental proof. A neutral body, if it were 

 a perfect nonconductor, would not be affected either way by the neighbour- 

 hood of an electrified body : for while the whole matter contained in it 

 remains barely saturated with the electric fluid, the attractions and repul- 

 sions balance each other. But in general, a neutral body appears to be 

 attracted by an electrified body, on account of a change of the disposition 

 of the fluid which it contains, upon the approach of a body either 

 positively or negatively electrified. The electrical affection produced in 

 this manner, without any actual transfer of the fluid, is called induced 

 electricity. 



When a body positively electrified approaches to a neutral body, the 

 redundancy of the fluid expels a portion of the natural quantity from the 



* On charge and distribution consult Winkler, Electr. Kraft des Wassers, Leipz. 

 1746. Beccaria, Ph. Tr. 1767, p. 297. Achard, Hist, et Mem. de Berlin, 1780, 

 * p. 47. Coulomb. Hist, et Mem. 1785, p. 612; 1786, p. 67; 1787, p. 421 ; and 

 the Analytical investigations of Poisson, Mem. de 1'Institut, 1811, 1, 163, 274 ; and 

 , Essay, 4to, Netting. 1828. 



