pound of plaster of Paris, and a quarter of a pint of linseed oil. Other cements in great variety, more or less fusible, &c., may be formed by combining the preceding ingredients in various proportions. The ochre and plaster of Paris should be well dried, and added to the other ingredients when they are well melted. 201. It must have occurred to those engaged in a series of Voltaic experiments, to observe the early exhaustion of power and the inequality of the action under the usual construction and management of the apparatus. The lecturer on this subject has more particularly felt such inconvenience; as during the progress of his experiments of elucidation he is obliged frequently to pause for explanation, during which time the power is on the decline.

202. To obviate these difficulties, Mr. Pepys has constructed a table, with drawers containing a suite of troughs, all the plates of which may be either raised out of the acid, or immersed into it, simultaneously. By means of a lever and counterpoise weight, the whole of the plates are as easily elevated as one series; all the communications with the prime conductors being, as in the same gentleman's Voltaic discharger, completed by quicksilver.

203. The troughs being enclosed within the table or chest, prevents the free escape of the acid vapors; and, where an opportunity offers of communication with a chimney or window, a pipe may be usefully added to carry them off. 204. Fig. 1, plate I., ELECTRO-GALVANISM, represents the external figure of the case.

205. Fig. 2. The internal arrangement of the whole contents (except the communication), the front being removed.

206. Fig. 3. Side view of the same, the side of the case, and drawers being removed.

207. Fig. 4. One of the drawers, with the spring supports, or props for the plates. 208. Fig. 5. Front view of the communica

tions.

209. Fig. 6. Side view of ditto.

210. The Voltaic series consists of sixty pairs of plates, four inches square, each plate presenting its whole surface to the action of the acid; they are arranged in two drawers A, A, one above the other, each drawer containing three porcelain troughs a, a, a, and each trough ten pair of plates b, b, b; the plates are suspended from rods c, c, c, connecting each set of ten pairs together, and these rods drop into a square frame 4, d, made to the full size of each drawer inside: the action of these frames lowers or raises the whole of the plates together, and is thus contrived.

211. B, B, are two rods passing through the upper board or table, and resting upon the short arm of the levers C, C, fig. 2, which are of wood; these rods have each two pairs of pins e,f; and which in fig. 2 are represented as employed, the plates being in action; but in fig. 3 the contrary, the lower drawer being open, and the frames, with plates supported by their props D.D. The drawers being first shut, the handles E, E, of the rod B, are to be turned inwards, as in fig. 2, when the pins e, e, enter the openings cut in the sides of the drawers at g, fig. 4, and stop

in the grooves h, h, fig. 2, cut in the square frame d, to receive them; in the mean while, the shorter pins f,f, bearing upon the lower sides. of the spring props D, press their upper end or points entirely within the thickness of the drawer on each side, and release the frames d, d. The whole weight of the plates, now bearing only upon the rods, is counterpoised by the weight w, which connects the two levers C, C; they are gradually let down into their several partitions, and the action of the battery commences; at the conclusion of the experiment the rods are again raised by the handles E, E, and when stopped, the pins e, having reached the top of the groove g, fig. 4, the handles are to be turned back into their former position, as in fig. 3; the props D, being now first released, shoot into the drawers, and support the frames when the pins e, e, have quitted them.

212. The communications between each trough are effected in the usual manner; but those which conduct the fluid from one drawer to the other, and from the opposite ends of the series to the upper board or table, are capable of being disengaged, and their connexions are effected under mercury, as in the Voltaic discharger.

213. They are thus arranged: i, i, i, are ivory cups containing mercury, and fixed to the drawers; j,j,j, are platina wires depending from them, and entering the troughs; k is a ring and wire, which effects the communication between the two drawers; and 1,, are the two wires which conduct the fluid from the opposite ends of the battery to the table, C being the copper, and the zinc end of the series.

214. We have stated that when the opposite extremities of a powerful Voltaic apparatus are connected by a wire, at the moment of contact a distinct spark is perceived, which occurs every time the contact is alternately broken and renewed. If the contact is made with a wire terminated at the end by a piece of well-burnt charcoal, the spark is considerably more vivid. And if two wires proceeding from the opposite ends of the battery are armed with charcoal points, and brought in contact with each other, the light evolved is more brilliant and intense than any that has been procured by other artificial arrangements. When the battery is powerful, the emission of light may be kept up for a considerable time; it is so dazzling as to fatigue the eye even by a temporary glance, and, when it ceases, leaves the most brilliantly illuminated room in apparent darkness.

215. This light appears to be principally derived from the immediate action of the Voltaic apparatus and not from the combustion of the charcoal; for, though that is partly ignited, it suffers but comparatively little waste, and the light is evolved with equal splendor when the experiment is made in gases which contain no oxygen; and will even take place, though with diminished energy, under water, alcohol, ether oils, and other fluids whose conducting power is not too great.

216. The influence of the Voltaic spark on various gases may be ascertained by the apparatus represented at fig. 1, plate II., ELECTROGALVANISM, the wires within the globe being ter