tery of jars so arranged that I should be able to take advantage of this principle, and make one jar charge another, instead of my being obliged to charge the whole series; for, though they are all connected together, and charged by the same operation in the common electric battery, yet the time and labour consumed in charging the battery is exactly the same as if each jar were charged separately and then added to the series. A great saving of labour and time would have been effected had the arrangement of jars answered, for it was exactly the same as that described by Brande, so far as the charging part of the apparatus was concerned; but when the jars were loaded, or rather should have been loaded, they were made to turn through a quadrant, and form a new arrangement, by which all their outside coatings were connected together by a common conductor. A similar arrangement connected all their inside coatings, which made all the conditions necessary to the perfection of the common battery; and I found it capable of being charged by the electrifying machine in this form; but it could not be charged to any extent in the other. It appeared that but few sparks would pass from the conductor to the first jar. If the last one was removed, and its chain fastened to the next, the first jar would take a few more sparks, and so on; for it was found that whenever the last jar in the series at any time was removed, the same results followed; and this was the case when the last but one was removed, clearly proving that the capacity or aptitude of the first jar to take a charge was influenced and diminished by the second, more so by the third, fourth, &c. Its aptitude was greatest when it was by itself, and not connected, as described, with the others.

"This result disappointed my expectations, so far as my intended improvement on the electric battery was concerned; and it also appeared to point out the existence of a principle influencing the charge of the electric jar, which was not recognized in the popular treatises on electricity. I procured a number of glass plates with fixed and moveable coatings. These plates were insulated and arranged with and without coatings in every way that Brande's rule required, but the general result was the same as that given above.

"From numerous experiments made with these plates, I came to the following general conclusions :

"1. That the actual quantity of the positive and negative electricities which we can accumulate in the opposite surfaces of an electric or non-conductor, as a plate of glass or dry ice, depends upon the distance of these surfaces.

"2. Every case of charge of one jar or plate may be assimilated to that of any number of jars or plates in a series such as Brande's, by supposing the one jar or plate to be divided into the greater number, its thickness being the sum of the thicknesses of all the segments or plates; the inside of the first jar or surface of first plate in contact with the conductor, and outside of last jar or plate in contact with the ground, being considered as the proper opposite sur

faces of the proper plate, and those on which the electricities evolved by the friction of the cylinder and rubber of the electrifying machine are accumulated or heaped.

"If we make a pile of the plates, coated or not, and charge the outside surfaces by coating them, and connecting one with the cylinder and the other with the rubber of the machine, we find all the conditions of the experiment complied with. There is no necessity for any connexion with the ground, which in Brande's can act merely as the conductor to convey the negative charge of the rubber to the extreme surface.

"Let us now unpack the pile, and we find that the charge of the intermediate plates diminishes as we approximate towards the centre of the pile, being greatest near the extremes. At equal distances the charges are equal; for the charges of the first plate but one, and the last but one, will as perfectly neutralize each other as the charges of the surfaces of the first and last. The same is found to be the case with the surfaces of the third plates from each extreme, and so on of the others; but it is not the case with a second and a third, a first and a fourth plate, and so on, no two unequals as to place exactly neutralizing each other. Hence we may conclude, that the charge of the intermediate jars in a series such as described by Brande, though it really depends on inductive agency, is altogether different from that kind he alludes to, which may be inferred from his erroneous representation of the actual fact; and the charge of the extreme surfaces is immediately the result of that action only, which several electricians have called conduction, arising from the connexion of these surfaces with the sources of the free electric forces.

"The fact here described appears capable of throwing much light on the corpuscular arrangement of the atoms of bodies which retain an electric charge on their surfaces, or which, by a change of form from mechanical pressure or difference of temperature, exhibit differences of electric state. In speaking of a charged electric, we may consider it a pile of an infinite number of plates, each of which, except the extreme surfaces, is composed of a surface of atoms, which are acted on by two sets of induced electric forces, whose differences, arising from their distances from the extremes, we discover when we split the plate, or if it be a pile, when we separate the plates from each other."

On the Progress effected in the Process of Gilding by the ElectroChemical Method. By Professor A. DE LA RIVE.*

I shall unite under this title the account given of the progress of this application of science to the arts since I made it known in April, 1840.

Different artists have been occupied on it at Geneva, particularly M. M. Bergem, father and son, who have presented the Academy

Archives De L'Ectricitie, No. 1.

of Sciences at Paris, in the spring of 1840, objects gilded, and which, after having been submitted to decisive proofs, have been acknowledged as nothing inferior in any respect, either in solidity or brilliance, to the best gilding produced by the mercurial method. These gentlemen have brought to the process which I have described some perfections which they have not made known. This mode of gilding appears to meet with some obstacles in its application to pieces of brass for the movements of clocks or watches, because the colour which it gives them is not such as is usually given to this species of work.

M. Droin, of Geneva, a distinguished workman, who is employed with M. M. Baute and Co., has succeeded, by following to the letter the process which I have described, in producing beautiful specimens of gilding; but he has remarked, that in order to succeed it is necessary to have the metal that we want to gild (silver or brass) perfectly homogeneous, a quality which it is difficult at all times to meet with. The gilding will not be perfectly uniform except under this condition.

M. Perrot, of Rouen, has sent to the Academy of Sciences of Paris many samples of different metals which he has gilded by voltaic currents, and which appear to have succeeded very well.

M. Arago likewise presented the Academy of Sciences, in its session of the 5th of May last, with the spring of a chronometer from the manufactory of M. Dent, gilded to great perfection by means of the galvanic process. He called to mind, on this occasion, that he had presented to the Academy a multitude of objects in metal, gilded by means of the same process by M. Perrot. M. Perrot had already at this time, also, springs to exhibit which were gilded in the same manner, and if they were not comprised in the number of objects which he sent, it was because he was awaiting the completion of an experiment in which he had undertaken to gild, at the same time, all the movements of a watch; to gild them not only whilst in their place, but whilst performing their usual functions.

In Germany, a distinguished artist of Stuttgard, Mr. Reinecker, who is the author of a very remarkable process of waving or watering, has brought the process of gilding by the galvanic method to that point of perfection which, under the relation of solidity, leaves nothing to be desired. As to its beauty, it leaves far in the rear every other species of gilding. "If we consider," adds the Gazette of Stuttgard (from whence we draw these details), "that in the process of gilding by galvanism there is no disengagement of those mercurial vapours so hurtful to the operator, that the quantity of gold employed is much less than in the ordinary gilding, and that the greater part of the technical portion of the work is so simple that it may be executed by children, this discovery in this branch of industry will then appear of such importance that we can but express our ardent desire to see it generally employed."

M. Boettiger, in the Annalen der Chemie and der Pharmacie (vol. xxxv., p. 350), describes the efforts which he has made to gild and platinize the plates of copper in relief which have been obtained by the process galvanoplastik.

He tried, at first, to platinize them by the galvanic method, making use of a solution of chloride of platina very neuter and very weak. He has succeeded, but he has found that it was necessary to have six immersions in the chloride of platinum to produce a covering of platinum of very small thickness; and again, this covering had not a very good colour, but rather grey than white.

Having found, by succeeding experiments, that for gilding no salt is preferable to the double chloride of gold and sodium, Mr. B. endeavoured to employ, in platinizing, the double chloride of platinum and sodium. The experiments which he has thus made have perfectly succeeded. In most cases he did not find it necessary to give more than three immersions to re-cover with a sufficiently strong layer of platinum the largest surface of copper; the colour also appeared of a much purer white. There is one circumstance, however, to which it is always necessary to pay attention in platinizing copper and other metals, which is, strongly to rub the object with a small piece of linen, and to scour it immediately with chalk each time, without exception, that it is withdrawn from the solution of platinum. It is worthy of remark also, that whether in silvering, in gilding, or in platinizing, those objects which have the highest polish are those also which take the metallic layer with the greatest facility and beauty. Mr. Boettiger thinks, that in order to produce good gilding on copper, it is necessary to commence by covering it with a cuticle of platinum, which is easy, and of very little expense; the gilding is far more beautiful and more durable than that obtained by the direct gilding of the copper. It is easy to obtain the double chloride of platinum and sodium by mixing equal parts of dry chloride of platinum and of pure common salt in distilled water. It is very necessary also to rub the metal conveniently with fine sand, moistened hydrochloric acid mixed with chalk, in such a manner as to leave no traces of the oxyde of copper, for platinum will not be precipitated on those places where any of it remains, and it will suffice to rub again those places, in order to determine this deposit of platinum, when the plate of copper is again put into the solution as the negative metal of the pair.

I cannot avoid remarking, that I have urgently insisted, in my notice, on the necessity of well cleansing the surface of the copper from verdigris before putting them into the solution of gold, and on the importance of successive immersions, and of the rubbing being repeated after each immersion with a fine linen cloth.

M. Snaer, in a work on electro-metalurgy, of which we shall give an account in our next number, employs for gilding voltaic currents far more powerful than those which I have indicated, and

which have been generally used. He is said thus to obtain gilding much more solid, and of any thickness, as great as may be required.

He remarks that the process called the English one, of Elphinstone, does not offer this last advantage. In this process the object to be gilded, which is brass, for example, is put into a solution of double chloride of gold and sodium, raised to high temperature. The gold is precipitated by the effect of the solution of a part of the metal equivalent to that on which the precipitation takes place. Now, as soon as all the surface is re-covered by a thin cuticle of gold, there is no longer a possibility of any part of this surface being dissolved, and thus the gold is no longer precipitated. It can only form, then, a very superficial gilding, and consequently of short duration; whilst by the voltaic process there is no limit to the thickness which may be given to the lamina of gold. Another inconvenience of the English process is, that there ensues, by the dissolution of a part of the surface to be gilded, an alteration of that surface, a circumstance which proves prejudicial in many cases, especially when it acts on objects the dimensions of which have been very exactly calculated, and ought not be altered, such as the wheels of chronometers, for example.

M. Hammon, an engraver at Geneva, has found great advantage in replacing the engraving by aquafortis, the varnish of which is made to cover the plate of copper by a cuticle of gold precipitated by voltaic agency: the tracings of the needle are far more delicate. The lamina of gold being permanent, and not being broken or carried off like the coating of varnish, when the aquafortis has operated, we may with great facility correct the engraven plate if it has any defect, which is impossible in the old process. We shall give to our readers, in one of our next numbers, a specimen of this species of engraving, by means of which we have produced a new apparatus which we purpose describing on a future occasion.

ROYAL VICTORIA GALLERY, MANCHESTER.
CONVERSAZIONE, FEBRUARY 16, 1841.

On a New Class of Magnetic Forces. By J. P. JOULE, Esq.

As it is my intention to bring forward in this paper an electromagnetic principle, in reference partly to the motion of machines, I hope that a few preliminary observations with respect to the present class of electro-magnetic engines will not be deemed out of place.

The great attractive powers of the electro-magnet, and the extreme rapidity with which its polarity is reversed by changing the direction of the current, very readily presents to the reflecting mind an idea that its power may be made available for mechanical purposes. Accordingly, as soon as the general principles of electromagnetism were understood, Professor Henry, Mr. Sturgeon, and