No, for the action will soon stop, as was explained before, unless a vent be given to the accumulated electricities. This is easily done, however, by establishing a communication by means of the wires (Fig. 1.), between the two ends of the battery: these being brought into contact, the two electricities meet and neutralize each other, producing the shock and other effects of electricity; and the action goes on with renewed energy, being no longer obstructed by the accumulation of the two electricities which impeded its progress. EMILY. Is it the union of the two electricities which produces the electric spark? MRS. B. Yes; and it is, I believe, this circumstance which gave rise to Sir H. Davy’s opinion that caloric may be a compound of the two electricities. CAROLINE. Yet surely caloric is very different from the electrical spark? MRS. B. The difference may consist probably only in intensity: for the heat of the electric spark is considerably more intense, though confined to a very minute spot, than any heat we can produce by other means. EMILY. Is it quite certain that the electricity of the Voltaic battery is precisely of the same nature as that of the common electrical machine? MRS. B. Undoubtedly; the shock given to the human body, the spark, the circumstance of the same substances which are conductors of the one being also conductors of the other, and of those bodies, such as glass and sealing-wax, which are non-conductors of the one, being also non-conductors of the other, are striking proofs of it. Besides, Sir H. Davy has shewn in his Lectures, that a Leyden jar, and a common electric battery, can be charged with electricity obtained from a Voltaic battery, the effect produced being perfectly similar to that obtained by a common machine. Dr. Wollaston has likewise proved that similar chemical decompositions are effected by the electric machine and by the Voltaic battery; and has made other experiments which render it highly probable, that the origin of both electricities is essentially the same, as they show that the rubber of the common electrical machine, like the zinc in the Voltaic battery, produces the two electricities by combining with oxygen. CAROLINE. But I do not see whence the rubber obtains oxygen, for there is neither acid nor water used in the common machine, and I always understood that the electricity was excited by the friction. MRS. B. It appears that by friction the rubber obtains oxygen from the atmosphere, which is partly composed of that element. The oxygen combines with the amalgam of the rubber, which is of a metallic nature, much in the same way as the oxygen of the acid combines with the zinc in the Voltaic battery, and it is thus that the two electricities are disengaged. CAROLINE. But, if the electricities of both machines are similar, why not use the common machine for chemical decompositions? MRS. B.