Researches in Electricity : Eleventh Series, 363 



The details are then given of a very elaborate series of experiments 

 with atmospheric air, oxygen, hydrogen, nitrogen, muriatic acid, 

 carbonic acid, sulphurous acid, sulphuretted hydrogen, and other 

 gases, undertaken with the view of comparing them one with an- 

 other under a great variety of modifications. Notwithstanding the 

 striking contrasts of all kinds which these gases present, of property, 

 of density, whether simple or compound, anions or cations, of high 

 or low pressure, hot or cold, not the least difference in their capacity 

 to favour or admit electrical induction through them could be per- 

 ceived. Considering the point established, that in all these gases 

 induction takes place by an action of contiguous particles, this is 

 the more important, and adds one to the many striking relations 

 which hold among bodies having the gaseous form. 



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 phsenomena 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 pheenomena relating to this subject will be reviewed. 



Jan. 18. — " 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. 



