this fact we easily understand that such non-metallic substances as will not dissolve in the liquid, if covered with a thin metallic film, or with a coating of graphite, will answer all the purposes of metallic originals.

Hence it is, that any non-metallic mould or pattern being so covered, and, by means of a suitable conducting wire made the cathode of a battery, will receive the reduced copper from the solution, which will cohere firmly together and form an exact metallic copy of the original from which the non-metallic mould was taken. The non-metallic substances which may be employed for this purpose, are clay or porcelain, slate, plaster of Paris, bees-wax, sulphur, stearine, sealing-wax, wood, &c., either in plates or any other artificial form. Any of these bodies employed as moulds or patterns are to have their surfaces covered with thin metallic leaf, or with soft impalpable metallic powders, or with powered charcoal or blacklead; which, in order to prevent the fine lines and angles of the mould or pattern being blunted, must be laid on carefully and exceedingly thin. It will be obvious that these foils or powders can only be of such metals, as has already been observed, as will not of themselves chemically decompose the cupreous solution. We may obtain powders for this purpose ready prepared in the shops, or we may easily prepare them ourselves. For instance, we obtain a very soft powder of copper by precipitating it from its nitrous solution by iron. Besides the metals, we may also prepare plumbago in a finely washed impalpable powder, which is much finer distributed, and attaches itself to the face of the mould much better than any of the metallic powders. When thus prepared, it may be mixed with water and gently smeared over the model. When the film of plumbago has become perfectly dry, should there appear a superabundance on any part, it may be removed by a soft pencil or brush. The plumbago will adhere well enough to some substances without being moistened with water, and may then be laid on dry by means of a soft pencil, which, previously, has been made a little clammy

with oil.

This

If the model or pattern be of plaster, it ought to be so prepared as to resist the introduction of the liquid for a long time. property is best acquired by placing the plaster mould in a hot mixture of stearine and wax, and permitted to soak as long as airbubbles are seen to ascend in this pure liquid. By this means the mould acquires a considerable degree of hardness, without losing any of the original sharpness of the design.

I have previously alluded to stearine as a substance which, when clothed with a metallic surface, can be employed in the galvanoplastik

art.

In again referring to this substance, I will here add, that when managed with caution, it produces castings from the softest design, which, for accuracy and sharpness, far excels any plaster casting whatever. My attention was first directed to this property of stearine by Count Alex. Bobrinski, to whose circumspect enterprising spirit, in spreading knowledge and promoting industry in his native

land, so many are grateful. The stearine, moreover, is susceptible of being well polished, turned, and, as it appears, of being engraved on-properties, in consequence of which, for this purpose, as well as in other respects, this material commands a high importance.

In the employment of non-metallic substances, some foresight is requisite in the application of the conductors which unite them to the zinc pole of the battery. However finely and equally the metallic powders, or the plumbago, may be distributed over the face of the mould, or pattern, they produce only an inferior conducting surface; and the reduction commences at those points only where this inferior conducting film is in intimate contact with the uniting conductor; and, consequently, the more we increase the points of contact, so much quicker will the surface of the mould be covered with reduced copper. I usually surround the model with a thin strip of rolled lead or copper, which easily bends to inequalities of the margin, and allows of being brought into intimate contact with the metallized or graphitized surface. It has still to be remarked, that the reduction proceeds with an uniform distribution, when we glue the original in a horizontal position, which position is particularly recommended, when the surface to be covered is of considerable dimensions, and in bold relief. All those parts which are intended not to be covered with copper-such as the connecting metal, the back part of the pattern, &c.—must be covered with wax, or other non-conducting substance, sufficiently to prevent any bare metallic parts being exposed to the cupreous solution; for, wherever there is an unnecessary deposit on such parts, it interferes with the action on the face of the model or pattern, and prevents the galvanic copy from arriving at the intended thickness. But we can, even under these circumstances, increase the thickness of the copper plate, especially where malleability is not a particular object. This is accomplished by strewing copper, in fine corns or filings, on the top of the first formed galvanic casing, which will very soon grow firmly to it, and become of the self-same piece.

IX.

The great variety of substances, partly plastic and partly otherwise manufactured, which can be employed in the galvanoplastik process, opens in this novel art, which may be considered as a cold metallic foundry, a field of infinite extent and interest, not only to the artist, but also in many other practical points of view. I will just point out a few instances of its practicability, which I have convinced myself of. Of the manner of copying engraved copper plates I have already noticed, and I will now add, that the same process is no less applicable to copying of medallions, coins, &c., whether of copper or of the noble metals. The galvanoplastik process can also be applied to the formation of matrices for single letters, or for entire stereotype plates; and again, the types themselves may be deposited in these matrices; or they may be used in the usual way as moulds for casting the letter type metal in.

Whether copper stereotype plates will deliver a greater number of sharp printed copies than can be obtained from the common type metal, is a question that can be determined by experience only. The pictorial stamps surrounding initial letters, and other typographical ornaments, and also those tools which bookbinders use, may, in future, be very easily made by the galvanoplastik process. The patterns may first be cut in wood, from which copper matrices may be taken; and from these again the required copper types will be easily obtained. Forms for tapestry and cotton prints are easily made by the same means, which affords an opportunity of their being procured in great variety, and to any extent. Maps and plans, en relief, of towns, have recently come into considerable repute, for the printing of which, the necessary forms and counterforms may be immediately obtained by depositing the copper, to the required thickness, upon a proper mould or pattern made of any suitable material. Bas-reliefs, and other objects in relief in the arts, can be immediately formed in copper in infinite variety, upon wax embossed originals, even, perhaps, without the aid of the chisel; and, indeed, with all the sharpness and delicate softness that the original received from the hand of the artist.

You have already been made to understand that the first form for all these purposes can be taken in plaster moulds. This substance is also applicable, in a similar manner, for obtaining metallic forms or moulds for the manufacture of stone-ware pots, and the pottery ware which are decorated with relief figures. The galvanoplastik process, moreover, places in our hands the means of decorating our buildings, both interiorly and exteriorly, with cheap and numerous copies of the finest specimens of ancient bronzes; and, as it were, opens an entirely new and extensive field for the cultivation of one of the finest branches of the arts.

That objects composed of inferior materials may, by this process, whether for the protection against the weather or for other purposes, become covered with copper, is a circumstance worthy of mention in this place. By the galvanoplastik process, notwithstanding the accuracy with which we procure copies of original objects, we see that on the reverse side of the galvanoplastik copy the deposited metal assumes a granular appearance, and it is only when the process is carried on very slowly, and the layer of copper is left quite thin, that there is any appearance of the outside of the copy having any corresponding features with the original. Notwithstanding, however, the partial inaccuracy at which we can only arrive by this method, objects thus overlaid with copper, when seen at a distance, will still present to the eye the true figures and proportions. They may be covered with a metallic skin of any required thickness, and any bold protuberances or other accidental roughness that may form can easily be removed by the chisel.

Hitherto I have treated only of such galvanoplastik processes as are applicable to obtaining simple copies from original forms or matters from which they are easily separated; for instance, from

engraved copper-plates, coins, medallions, seals, wood-cuts, &c. Were we to aim at the manufacture of entire figures, such as statues and other entire objects, for which a complicated mould, consisting of several pieces, would be required, the difficulties attending the process would be much greater than in those simple cases hitherto described: nevertheless, in the most complicated cases the difficulties that would probably be met with do not appear to be insurmountable. From a wax embossed bust, en haut relief, and much underworked, I have obtained a tolerably good galvanoplastik figure, though, it is true, not entirely free from blemish, in the following manner :-The original wax bust being well covered with plumbago, and furnished with a conductor, was submitted to the galvanoplastik process. When the whole had become covered with a thin skin of copper, the wax was melted out, leaving a hollow copper mould corresponding to the original wax figure. After washing out this mould with spirits of turpentine, it was again submitted to the galvanic action, as a cathode, in order that the precipitation might proceed within. When the process had continued long enough for the interior figure to be of the required thickness, the outer case, which had served as a mould, was loosened, and removed piece-meal, which, in some places, could not be accomplished without some degree of force. By these means, however, I obtained a true and perfectly smooth copy of the original, which in some few places only was a little deranged, from causes that may, in future, be avoided. It is true that by this method we lose both the original and the first formed metallic mould in every copy that we obtain; but it is to be hoped that this circumstance will be no hindrance to the diffusion of the advantages to be gained by the galvanoplastik art, from which so much may reasonably be expected, and in which process the workshops and laboratories of the artist and the handicraftsman will still be productive of many accomplishments and facilities which, as yet, can only be viewed in prospective.

ELEMENTARY LECTURES ON ELECTRICITY, &c.

LECTURE XIV.

Before proceeding any further in the experimental department, it will be necessary that I explain to you some other pieces of apparatus that will be wanted as we pursue our illustrations. Here we have a very beautiful, and, for many experiments, an exceedingly useful piece of apparatus, called the universal discharges. (See fig. 1.) A mahogany board constitutes the

base of this instrument. Near to each end of this board is fixed a vertical glass pillar, surmounted with a brass piece, consisting of a socket for the introduction of the upper end of the pillar, an universal joint, and a small spring tube for

the reception of a brass rod. The brass rod moves freely in the tube, and is furnished with an epening at one end, and a small brass ball at the other; the latter screws on to the wire, which is pointed, and is occasionally removed for certain experiments in which points are required. From the centre of the base board rises a short wooden pillar, which carries a small table, for the purpose of placing on it certain objects of experiment. If, now, 1 raise the balls of both wires from the table till their wires are nearly horizontal, and place the balls at about an inch apart, sparks, which are taken from the prime conductor to one of the rings, will be seen darting between the two balls, and will pass off invisibly to the ground, through the other wire, and such other intermediate conductors as form its uninsulating connection. If the balls be brought closer together, the sparks will be smaller and more frequent; and if they are removed further asunder, the sparks will be more powerful and brilliant, will make a greater noise, but will pass less frequently than before.

If, now, I unscrew both balls of the brass rods, and expose the points to one another, we shall have a very beautiful display of the brush and star; the former issuing from the wire in connection with the prime conductor, and the latter on the point of the uninsulating wire. By means of this convenient piece of apparatus, many of those experiments shewn in our last lecture are very easily and more elegantly performed. To perforate cards and other solid bodies, for instance, they may be very conveniently placed between the balls of the universal discharger, with their lower edges resting on the table of the instrument, and gold leaf placed between pieces of glass is easily prepared for the reception of an electrical discharge by means of this instrument. As I have another fact to notice in the perforation of cards, we will employ the universal discharger in the experiment.

I will place a card vertically between the balls of the universal discharger, which do not press firmly against it, but merely prevent it from falling whilst its lower edge rests on the small table. Thus arranged, I discharge the jar through the card, and the usual perforation is made; but by close observation you will find that the card, about the edges of the hole, is protruded on both sides, as if the electric fluid had passed in opposite directions. There are but very few experiments in electricity that have made so much noise as this and its trifling variations. It has been the means of leading philosophers to very different opinions respecting the cause of the two burs on the opposite sides of the card, and has, consequently, been a subject for much ardent discussion. Dr. Franklin was the first person who pierced a card by an electrical discharge, but the protrusion of the card on the opposite sides was first observed by Mr. Symmer; indeed, on one of the cards which had been pierced by Dr. Franklin's experiments. Mr. Symmer made many experiments of this kind, varying them in many ways, all of which produced similar effects, and led this electrician to infer that there are two