which moment the discs appear to attract each other. But if the discs are both charged with the same kind of electricity, the diver- gence of the electroscopes increases, and at this instant the suspended disc recedes from that which is fixed, being apparently repelled by it.
The author proceeds to examine strictly the nature of this in- ductive influence, and adduces experiments to render probable that it is in some way dependent on the presence of an exquisitely subtile form of matter which may become disturbed in bodies, and assumes new states or conditions of distribution.
Very numerous experiments are detailed, showing the influence of changes of difi^erent intensity, of changes in the dimensions and di- stances of the opposed discs, of interposed bodies of diflferent forms, &c. on the phenomena of induction. The author concludes by giving the following formulae as the results of his investigations regarding the elementary laws of electrical induction and attraction. In these expressions Q = quantity of charge, T = the direct induction, q = the quantity of electricity displaced, t — its intensity, T" = the reflected induction, = the disturbed quantity, = its intensity, q^' = the total quantity in the opposed charged surface, A = the surface, D = the distance between the opposed points, F = the force of attraction.
For the direct induction :
-v/D D For the reflected induction :
. Q . Q
A - 9 - jD ^ - 1). ^ >/D
For the attractive force between a charged and a neutral free conductor :
_ Q2 F — —
F - ^ F -
For the force between two unchangeable surfaces, one positive the other negative :
2. " On the Conditions of Equilibrium of an Incompressible Fluid, the particles of which are acted upon by Accelerating Forces." By James Ivory, Esq., K.H., M.A., F.R.S., &c.
The intention of this paper is to examine the principles and me- thods that have been proposed for solving the problem of which it treats, with the view of obviating what is obscure and exceptionable in the investigation usually given of it.
The principle first advanced by Huyghens is clearly demonstrated, and is attended with no difl^culty. This principle requires that the resultant of the forces in action at the surface of a fluid in equili-
