and fluid on the inner surface of the jar a, rushes through the discharging-rod to the negative outer surface of the jar d: and the redundant fluid of the inner surface of d, supplies the deficiency on the outer surface of the jar e, and so on throughout the series and although perhaps we may not find an exact equilibrium establshed on the two surfaces of every individual jar in the series, the process accomplishes their discharge as completely as by applying the discharging rod to each jar separately: and which is an additional proof, though an indirect one, of the jars having become charged by each others electric fluid and it is a direct proof, as far as experiment is capable of proving any thing, that the restoration of a general equilibrium in the series, has been accomplished by a return of the previously expelled fluid, to its original abode on the outer surfaces of the jars.

If, instead of the jars touching one another, as in our last experiment, we were to place them at a short distance from one another, we should see a series of sparks traversing the thin plate of air interposed between the coatings of one of one jar and the ball of the other, during the whole period occupied in the process of charging; and when the disharge takes place by connecting one ball of the discharging rod with the chain attached to the coating of the last jar (d), in the series, and with the other ball approaching the knob of the first jar (a,); the whole of the spaces between the several jars will become highly and simultaneously illuminated. This experiment has a very beautiful effect when performed in a darkened room. The noise produced will be in proportion to the size and number of jars employed in the series.

In all these operations of the leyden jar whilst in the act of charging, either directly from the prime conductor, or indirectly from the electrical influence of that apparatus, through the medium of other intervening jars; we find no difficulty in tracing a progressively increasing polarization of the opposite sides of each individual jar; which become possitively and negatively electrical alternately, whatever may be the extent of the series: and when the polarization is at a maximum, the jar is as fully charged as the machine is capable of carrying on the charging process Hence you will easily understand that the charging of a jar to a high degree requires a proportional facility of becoming polarized by the energies of the machine; which facility appears to be effected by an attention to two principal circumstances:-the thinness of the glass, and the connection of the outer surface with the ground; which circumstances are analogous to those that are required for the electro polarization of metallic bodies, as already illustrated in former lectures: for in those cases a thin plate of air between the bodies becomes electro-polar as decidedly as the metals themselves; and the facility of polarization is enhanced by the last metal in the series being in good conducting connection with the ground,

Another very interesting experiment is to be performed by having two jars so united with one another and with the prime conductor as to enable us to charge the one independently of the other. If, for instance we have a small metallic stage fixed to the wire belonging the inside of the large jar (a), fig. 3 plate VI. and upon that stage we place the smaller jar (b); we can very conveniently charge the large jar (a) by connecting its inner surface with the prime conductor, by means of a copper wire; and as the inner surface of the jar (b) is insulated it wil receive no charge, with the exception of a small portion of the fluid which rests on its outer coating by being in metalic connection with the prime conductor and inner surface of the jar (a,).

In this condition of things, the small jar, though not charged according to the general acceptation of the term, is nevertheless in a state of polarization; and its inner surface is negatively electric; for the fluid naturally belonging to that surface has been expelled as far as circumstances will allow, and a portion of it will be found in the ball (o,) which is in an electro positive state. Hence, the metallic apendages belonging to the inner surface of the jar (b,) are electro-polar and as the two surfaces of the glass are also electro-polar in the same direction, being under the same powerful polarizing influence of the accnmulated fluid on the inner surface of the lower jar (a); the inner surface of (b) has a strong tendency to part with its own fluid, and is in an excellent condition to discharge it

suddenly to any negatively electric body that may be brought within the sphere of its influence. To show you this fact I place the lower ball of the dischargingrod on the metallic plate on which the jar (a) is standing, and then make the upper ball approach the knob (o,) of the jar (b); and again we observe a bright flash of light and hear a report,-the usual attendants of an electric dicharge; which in this case has been a discharge of a portion of fluid from the inner surface of the jar (b.) to the other surface of (a.) Therefore both jars are now charged, the inner surface of (a.) and the outer surface of (b), being electro-positive, and their opposite sides consequently electro-negative: and both jars may be discharged either separately, or at the same moment; accordingly as we apply the discharging apparatus. If I join the inside of the upper jar (b), with the outside of the lower jar (a), by means of a metallic chain, or wire and after placing one ball of the dischaging-rod on this chain I bring the other ball towards the stage on which the small jar stands, or towards any of the metallic appendages joining the inside of the jar (a) and the outside of the jar (b): you find that the usual phenomena of discharge takes place and by examining the jars afterwards we shall find that both are as neutral as jars usually are after the first application of a discharging rod.

Let us now charge these two jars again, by the same means as before, in order that I may give you a specimen of the curiosities displayed by discharging them seperately. I will first apply the discharing rod to the outside of the jar (a and then I bring the other ball of it to the stage connected with its inside, the flash and report are produced, and the jar becomes discharged by a metallic connection between its inner and outer surfaces. But the moment I remove the discharging-rod, the jar (a,) again becomes electro-polar by the electric influence of the upper jar (b). I now apply the discharging-rod to this jar in order to discharge it also: and by a few moments metallic connection of its two sides, we find that both jars are rendered nearly mentual.

I will now again charge both jars as before; but in the discharge I will pro. ceed in a very different manner to any I have hitherto shown you. I first apply the discharging-rod to the two sides of the upper jar (b), and discharge it in the usual way, by transporting the redundant fluid from its outside to its negative, inside, and thus restoring the equillbrium of the two sides. But the moment I take away the discharging-rod the jar (b) again becomes electro-polar, in the same manner as when first under then infinence of the lower jar (a): but as this latter jar has lost a portion of its contents by supplying the small jar (b) with the previous charge, the polarizing influence is not now so great as at first: and, consequently, the tendency of (b) to dispose of its inner-surface fluid is also proportionally less. However, you will observe a bright flash and smart report by again applying the discharging-rod to the outer surface of (b) and the ball (0) of the small jar (b); and the latter again becomes charged. I will now again discharge the jar (b) and render it neutral as before, by conveying another portion of fluid from its outer surface. The charge of the large jar (a) having now lost another portion of its fluid, has consequently suffered a corresponding relaxation of its polarizing influence, and communicates to the inner surface of the jar (b) a still less tendency than before, to dispose of any of its electric fluid to other bodies. Notwithstanding, however, this diminution of electric force in the large jar (a) by every successive partial discharge through the medium of the jar (b), the phenomena may be repeated many times over before a complete neutralization takes place; and (especially when the lower jar is large and the upper one very small. It is an experiment of great interest and highly favourable to the theoretical views which Franklin entertained of electric actions.