Page:Proceedings of the Royal Society of London Vol 4.djvu/64

Rh In conclusion, the author remarks, that induction appears to be essentially an action of contiguous particles, through the interme- diation of which the electric force originating or appearing at a cer- tain place, is propagated to or sustained at a distance, appearing there as a force of the same kind and exactly equal in amount, but oppo- site in its direction and tendencies. Induction requires no sensible thickness in the conductors which may be used to limit its extent, for an uninsulated leaf of gold may be made very highly positive on one surface, and as highly negative on the other, without the least inter- ference of the two states, as long as the induction continues. But with regard to dielectrics, or insulating media, the results are very differ- ent; for their thickness has an immediate and important influence on the degree of induction. As to their quality, though all gases and vapours are alike, whatever be their state, amongst solid bodies, and between them and gases, there are differences which prove the existence of specific inductive capacities

The author also refers to a transverse force with which the direct inductive force is accompanied. The experimental proof of the ex istence of such a force, in all cases of induction, is, from its bearing on the phænomena of electro-magnetism and magneto-electricity, of the highest importance; and we cannot but look forward with the greatest interest to the promised communication in which these and other phænomena relating to this subject will be reviewed.

Bryan Donkin, Esq,; Sir John Jacob Hansler; the Rev. George Henry Sacheverell Johnson, M.A.; and George Richardson Porter, Esq., were severally elected Fellows of the Society

"On the Variation of a Triple Integral." By Richard Abbott, Esq F.R.A.S. Communicated by Benjamin Gompertz, Esq., F.R.S.

In the calculus of variations, the discovery of which has immor- talized the name of Lagrange, that illustrious mathematician, by differentiating the function with respect to a new variable which en- ters into it, reduced the general problem of indeterminate maxima and minima to the solution of an equation depending on the variation of the given integral, whether single or multiple, and whose differ- ential coefficient contains any number of variables, or which even de- pends on other integrals. The author investigates, in the present memoir, the case in which the given function is a triple integral; its variation being composed of two distinct parts, namely, a triple inte- gral and another part, the determination of which must be sought from the limits of the triple integral

Explanation of the Phenomena of Intermitting Springs." By