may refer to the numerous admirable copies of engraved plates and medals already before the public: if any of these specimens be examined with a glass, it will be found that not only every line of the graver, but every scratch in the polished surface of the original plate, is faithfully transferred, both to the deposited matrix and the subsequent copy of it; and when we consider the fact that both these copies are of the same material as the original plate, and that that may just as well have been of a much softer and more workable material, we must immediately conclude that there is no other known mode of copying possessing like advantages. But as the application of it to the coping of engravings, medals, wood-cuts, and similar subjects, is already well known, I merely refer to it in illustration of my views, and will now offer a few reasons for supposing that it may eventually be found an economical process for some of the more ordinary branches of our manufactures in metal.

"I can now only explain the principles which lead me to imagine that it would not be a costly process on the large scale. In my preliminary experiments, I have used Mr. Smee's battery of platinated silver and zinc; excited by diluted sulphuric acid, it acts well and is more convenient than the sulphate of copper batteries.

"Mr. Spencer's very simple and cheap arrangements, in which the negative plate of a single pair is that receiving the deposit, is, I think, very suitable for flat work; but for complicated forms, I should certainly prefer having the battery arrangement separate from the depositing cell, both on account of its being more manageable, and because in this way the solution of the sulphate of copper is kept constantly at the point of saturation by the destruction of a portion of the copper plate connected with the negative plate of the battery. Of course the solution of this plate is effected by the portion of acid set free by depositing its copper on the mould, assisted by the galvanic action, so that in fact this method gives us the power of removing the material from any old and irregular piece of metal, and depositing it in the most highly wrought mould of which we may wish to obtain a copy.

In taking a comparative view of the probable cost of production, it will not be necessary to consider the first outlay for apparatus and moulds, because there must be a much larger outlay before commencing operations in the usual way; and leaving this out of the question, the cost of any electro-deposit would be made up of the value of the raw material, of the zinc and acid used in the battery, and of the time employed in making the arrangements.

"The raw material may be obtained in considerable quantities, at its lowest price, as old sheathing copper would be admirably adapted to the purpose, on account of the facility with which it may be bent to any required form. The zinc and acid used in the battery would only have combined to form sulphate of zinc, which would be of some value. The time required for making the arrangements in the different troughs of a large factory would be

comparatively small, because one man may keep a great number at work, as they only require attention once in twenty-four hours -of course there must be many other persons employed in such a factory, in preparing new patterns, and new battery plates and connections; but these come under other heads of expenditure which have their counterparts in the present mode.

"I will now suggest a few of the plans which may be used for producing hollow vessels. The most simple process which has occured to me, and the one which I have already used with success, is to form a block of some easily fused material into the shape of the interior of the required vessel, which serves as the matrix for depositing the copper on; when this is sufficiently thick, it may be placed on the fire till the block is melted, when the fluid material may be poured from any of its openings, and leave the hollow vessel complete and in a single piece, without the aid of the soldering iron or hammer. The temporary block on which this vessel is deposited may be formed of wax, cement, fusible metal, lead, or any other convenient material which melts at a much lower temperature than the metal to be deposited. I consider this method to be peculiarly applicable to the most complicated forms of metallic musical instruments, and to crooked tubular work generally; but it has certainly the great disadvantage of requiring a new mould for every repetition of the work, or rather a new block, for these may in many cases be cast in a mould which would be permanent for any number of repetitions. There is, however, one means of avoiding this in some cases, which is very well illustrated by the common boot-tree; if this were put together, and after having its surface metalized, placed in the depositing trough for a proper time, we should certainly have it covered with copper: we may then take out the centre or key piece, which would unlock the others, and they may readily be removed, leaving a copper bootnot a very desirable article certainly, but the block may just as well have been formed to a more suitable shape. Still there are disadvantages in this mode of procedure which would limit the application to a few articles, although there are some which could not readly be accomplished in any other way. For the production of ornamental vases and other works of value, I would suggest the following method:-Let the whole, or a segment of the work, according to the nature of the design, be moulded in wax, carved in wood, cast in plaster, or produced in any more convenient way; then metalise the surface, and deposit on as large a portion of the original as will relieve in one piece; repeat this at different times over the whole work, and so manage the edges of each piece that the whole shall key together in the usual way, so that when finished you will possess a metallic mould for the required work. Should the design be complicated in form, a number of pieces will be requisite; but there are many very expensive articles which would readily relieve if the mould were in a single piece, and a very

R

much more extensive class which may be made in two parts. Of course the inside of the metallic segments would correspond in polish and finish to the original model, and the metal mould, when complete, would serve for an unlimited number of copies, which would not require any cleaning up or hand finishing; but the parts would require to be put together, which I propose to effect by the same power that produced them. This, I think, may be done by covering the work with wax varnish while warm, and afterwards carefully cleaning all the edges, and then binding it together as if for soldering. The joints must now be touched over with nitric acid, and the article properly connected with the battery, and placed in the depositing trough; copper will immediately begin to deposit on the joints, and in a few hours, I imagine that these joints would be quite as strong as any other part; if so, the method would have the decided advantage of joining the work with pure copper, and of doing this without exposing any part of it to the fire. I have not yet attempted to join any work in this way; but I consider that I have good evidence of its practicability, in the well known fact of deposited copper uniting with any other portion of copper which has been cleaned with nitric acid, quite as intimately as the different parts of the original piece are united.

66

In the foregoing remarks I have endeavoured to shew that the system of electro-metallic deposits is capable of producing every article which leaves the workshop of the copper-smith, and that there is no very apparent reason for supposing that it would be too costly to compete with the usual process of manufacture; still much of this opinion is speculative, and as yet I have not sufficient experimental evidence to offer in support of it; but such as I have has fully satisfied me that it is correct. The small toy which accompanied this paper was made a few days before the meeting, and I believe it is the first symmetrical copper vessel ever produced by galvanic action.

16.-Hosking's Reversing Clutch Box.

The remaining articles of this valuable volume are constituted of accounts of the finances of the Society.

Notice on some Experiments made with a powerful Battery of Groves' Contruction. By M. le Prof. A. DE LA RIVE.*

I have availed myself of a circumstance which enabled me to mount a Groves' battery of forty pairs, to make with this piece of apparatus a certain number of experiments, some of which appear to me to be new. I do not speak, at this moment, of any others but those which have relation to calorific and luminous effects alone; I defer speaking of those which have chemical effects for their object until they are more complete.

• Archives De L'Electricité, No. 1.

I became convinced that we cannot obtain the luminous arc between the two points of charcoal, until after the two points have been in contact, and become reciprocally heated around the point of contact. We may then, by separating them gradually, succeed in obtaining between them a luminous arc of three centimetres.. With a more powerful pile this arc is still longer. Wood charcoal, after having been brought to a strong red heat, and then soaked in water, is that which gives the most brilliant light. Wood charcoal, unsoaked in water, is not a sufficiently good conductor of electricity to allow of its employment in this experiment. As to coke, it succeeds as well as the soaked charcoal, but the light which it gives is not so brilliant, and more especially not so white as that which we obtain from wood charcoal dipped in water; it is always of a blueish tinge, and but slightly inclined to red.

The transportation of particles of charcoal from the positive to the negative pole, during the time that the luminous arc is produced, is evident, but is still more sensible if the experiment is made in vacuo. We may observe the formation of a cavity, on the point of the positive piece of charcoal, which presents the appearance of a hollow cone, into which we may almost exactly insert the solid cone which is formed by the particles of charcoal accumulated at the negative point. The phenomenon is almost the same in the air, except that the accumulation of charcoal is less strong on the negative point, in consequence of a portion of the molecules being burnt during their transit; and the positive point presents only a plain surface in the place of a hollow one. This latter effect probably proceeds from the combustion of the thin envelope of the hollow cone, which ought to be formed in the air as well as in

vacuo.

It appears very probable that the luminous arc itself is only the result of the incandescence of the particles of charcoal transported from one pole to the other, which incandescence is accompanied by a partial combustion, and which takes place without combustion when the experiment is made in vacuo. The movement of these particles in the direction indicated is almost visible to the naked eye, when the current is not very strong. This transmission of the particles does not take place, as we have seen, except when the charcoal has previously been brought to a high degree of heat, a circumstance which probably, by diminishing the cohesion, facilitates the disjunction of the particles.

Charcoal is not the only body which presents the phenomenon of a luminous arc batween the two points, brought into connexion with the poles. Spongy platinum, as well as copper reduced by hydrogen to an impalpable powder and then filled in tubes of glass, produce the same effect. It appears necessary that the substance employed should possess but little cohesion, in order that the molecules may be easily detached by the current.

An indispensable condition for the success of the experiment is, that the substance possessing only slight cohesion be at the positive pole, it being of little import whether the substance at the negative pole be a similar one, or a body which is highly cohesive, as for instance, a morsel of forged metal. Thus we may have a luminous arc of one or two centimetres by putting at the positive pole a piece of spongy platinum, and at the negative pole a ball of the same metal forged. We can only obtain a very short spark by adopting the inverse disposition of the bodies. We see, in the first case, that the pieces of spongy platinum become hollowed by the effect of the departure of the metallic particles, which quit it in order to be transported to the ball which is on the negative pole. It is always necessary in these experiments, as in those where charcoal is employed, that the points communicating with the poles be brought into contact, before they have the power, in being separated, to produce the luminous arch.

I have repeated the beautiful experiment of the influence of the magnet on the luminous arc which occurs between the points of charcoal. This experiment was first made by Sir Humphry Davy; but the first idea of it belongs to M. Arago, who had been conducted to it by the analogy between the light produced by it with that of the aurora borealis, and by the observation which he had long before made, that the aurora borealis acts on the magnetic needle. We give the note which M. Arago had published before the lecture of Sir H. Davy to the Royal Society, in which the illustrious English chemist reported the experiment of the action of the magnet on the luminous arc of the pile. (See the end.)

I have found that, in effect, the luminous arc which is produced not only between the two points of charcoal, but also between two points of spongy platinum, or between two agglomerations of copper in powder, was influenced by a magnet, sometimes attracted, sometimes repulsed, following the pole of the magnet. The attraction or the repulsion exercised on the molecules themselves, though very distant, may be able to conduct the current; and that which goes to prove it is, that if the attraction or the repulsion remove them too far from each other, then the current no longer passes, and the luminous effect ceases. We may thus easily cause the disappearance of the Inminous arc, by merely moving the magnet.

I will not terminate this short notice without adding that I made an observation which M. Arago has, I believe, already made, to ascertain whether the light of the luminous arc which escapes between the charcoal points is not polarized. This fact is not in opposition with the idea that this light is due to the incandescence of the particles which are transported. In fact, these particles, being very distant, are isolated, so to speak, independent of each other, like the particles of gas. Now, in similar circumstances lihgt is not polarized. It will be so if it emanates from the particles of a solid body during incandescence, such as a metaliic wire,