no effect was produced inside of the tumbler. 6th. The wires were fixed between two strips of glass well tied together, but no effect was produced by 100 revolutions of the machine; but by placing the wires and glass under water, twenty revolutions produced an effect upon each piece of glass, and 150 revolutions split one of them to pieces. 7th. The wires were next fixed to a piece of plate glass oneeight of an inch thick, and placed under water. By 500 revolutions it was pierced to about one-third of its thickness, on the wired side; the other side not being affected.

Mr. Crosse observes, that although a regular stream of fire apparently passes between the metallic points, in reality it is a succession of small explosions, at each of which, the water is forced in one direction, and the glass in another; and also the wires have a strong tendency to be separated from the glass to which they are attached; and the effect on the glass between the points is proportional to the contiguity of the wires to the glass, as well as to the strength and number of the successive small explosions.* If the wires exceed the distance of one-twentieth of an inch from each other, the electric force necessary to leap across the interval will often break the glass, and at all events pierce an irregular hole. The wires also have another tendency, which is to unite and slightly solder together, even under the water. It is therefore absolutely necessary that they should be perfectly secured in their places. When the glass is thin, a series of vibrations is communicated to it, sufficiently powerful to separate a small portion of its substance from the opposite side; but when plate glass is used, this effect does not take place; apparently on account of its not being susceptible of being thrown into similar vibrations; and as it presents a stronger resistance, the effect is produced on the same side on which the wires are fixed.

an inch.

Mr. Crosse next fixed the wires very firmly on the side of a perfectly transparent crystal of quartz, at a distance of one-twentieth of After 100 revolutions, a small mark was visible between the wires, but the surface of the crystal remained smooth. I then immersed it in a glass dish of water, and passed 100 revolutions acrosss it. On examination I found a very sensible excavation between the wires, on the same side of the crystal. After 500 revolutions it was pierced to a much greater depth, and with a much larger excavation than the glass in the last experiment. This increased effect was produced by the wires having been more firmly secured on the surface of the crystal. I am inclined to think, that with a proper apparatus, well contrived to secure a firm pressure of

• Those readers who have perused my fourth memoir, " Annals of Electricity, &c.," vol. iv, p. 178, will find that several of my statements are in perfect accordance with the results of Mr. Crosse's experiments. We have the lateral effects of these miniature explosions, perforating solid bodies, throwing up water, and even separating the wires from the glass, in the manner that I showed lightning conductors would be peeled from the mast of a ship.

both wires on the substance experimented on, and by a proper regulation of the distance of the extremities of the wires, together with a sufficiently powerful stream of electricity, two or three times interrupted, not only glass may be sufficiently, easily, and readily drilled, but even the diamond and other gems may be perforated in the same way.

ELEMENTARY LECTURES ON ELECTRICITY, ETC. LECTURE XVI.

The experiments shown on strips of gold or silver, may be varied by employing their wires instead of metallic leaf. For this purpose the thinnest watch pendulum wire that can be procured is exceedingly useful, as it can be fused by the discharge from a moderate sized jar.

We will first discharge a large jar through a piece of this steel wire about ten inches in length, and you will find that the wire is barely made visibly red hot, although the intensity of the charge was tolerably high. Now the reason of our not succeeding in fusing the wire by this discharge, was not because of its being too thick, but simply because it was too long; and in order to convince you of this fact I will shorten it by one half, leaving a length of five inches only to be traversed by the next discharge of the same jar; the intensity of the charge being the same as in the former case. The result is as was predicted, the wire is fused, and you will have observed also, that the mechanical action was so great as to scatter the globules of the fused steel to a great distance on every side. We will presently make a similar experiment on a larger scale, but I must first vary it with the same jar.

Now in varying the experiment I will simply introduce a piece of wet thread to the circuit, in order to abate the mechanical action of the discharge, as on a former occasion. In this experiment I will operate on the five inches of wire which was cut off from that employed in the last experiment. Now, observe attentively, that the intensity of the charge is quite as high as before, indeed, somewhat higher; but the visible effects on the wire, by the discharge of the jar, are simply a few tremulous motions, and not the slightest indication of redness from an elevation of temperature are perceivable. Here again is another proof of the influence of electro-mechanical action in accomplishing the fusion of metallic bodies by ordinary electric discharges.

When experiments of this kind are carried on for the purpose of ascertaining the effects of certain electric charges, on wires of different

The last paragraph but one of lecture XV, p. 253 ought to have read thus. "I know of no other experiments by means of which I could show you, to greater advantage, that the calorific effects on the gold depend on the electro-mechanical action of the discharge."

dimensions, the balance electrometer of Cuthbertson (see p. 250), will be found very convenient. There is also another circumstance to be noticed in experiments of this kind. If the air within the jar be perfectly dry, the quantity of electric fluid that it will contain will be somewhat less than if the air were a little moistened, either by breathing into it, or by any other means.

Let us place the bent arm of the balance electrometer in connection with the prime conductor of the machine, the inside of the jar also being in connection with it. I will place about two inches of watch pendulum wire between the insulated ball of the electrometer, and the outside of the jar; I will also adjust the sliding weight on the graduated arm of the instrument to fifteen grains. Now, it will be obvious that when the charge has arrived sufficiently high for the repulsive action between the balls P and c, to overcome the load of fifteen grains, that they will separate by the upward motion of the ball c; and when the ball D, at the other extremity of the balance arm, has, by its descent, arrived sufficiently near to the insulated ball q, as to be within the striking distance, the discharge will take place, and the contents of the jar will traverse the steel wire. These arrangements being complete, and the route of the electric fluid being understood, we will now proceed to the experiment. A few turns of the machine causes the ball c to move, and a few more, you will observe, accomplishes the discharge. The steel wire is not only made red hot, but is fused, and partly scattered in small globules.

If now, we were now to add another inch to the length of the steel wire, and transmit through it a similar discharge to that employed in the preceding experiment, we should find that the wire would become just red hot, but not fuse; and to satisfy ourselves on this point, it is necessary to repeat the experiment two or three times. This being done, and still the wire remains perfect, so that it is pretty certain a discharge measured by fifteen grains is not sufficient to accomplish its fusion. We will now slide the weight to twenty grains, and having charged the jar to that point, the discharge through the steel wire immediately accomplishes its distruction.

Now in order to show that a jar will hold more of the electric fluid when moist within, we will first try how long a piece of wire can be fused, by the highest intensity of the jar when dry; and afterwards moisten the air within the jar, by breathing into it, and the experiment will prove that the discharge from the moistened jar, will fuse a much longer piece of wire than one from the dry jar.

When the coated surface of glass is very extensive, as in a battery of jars, for instance, this class of experiments can be exhibited on an extended scale, and with the most brilliant results. If for instance, we were to connect the inside of the battery (p. 176) with the prime conductor, and place the sliding weight at about forty grains, we should be enabled to fuse thin steel wire above forty

inches in length. To convince you of the beauty of this class of experiments, I will place a piece of iron wire, two feet long, in the circuit. Now observe attentively what takes place. Did you ever behold such a splendid sight? The wire, you will have observed, is first heated to the brightest redness; progresses perceptibly to an intense white; swelling in thickness to six or eight times its original dimensions, and eventually, it bursts into thousands of minute balls which became projected in every direction, and fell in a shower of fire.

The beauty of this experiment is considerably enhanced by coiling the iron wire into the shape of an open helix, like a cork-screw. You will observe that when the discharge has passed through the helix, the latter retains its shape for a perceptible time, more than a second for instance, before it bursts; which done, it is dispersed into a multitude of fiery globules.

By transmitting similar discharges through wires of platinum, gold, silver, copper, brass, &c., their fusion is very readily accomplished; and when very thin they are converted into a cloud of smoke, which becomes dispersed on every side in the surrounding air. Now, by making a series of experiments on these different metals, whilst suspended in the air, and in a darkened room, we shall see that each metal, during fusion, yields a peculiar coloured light. The platinum wire, you will observe, yields a whitish light, not very intense. The gold yields an orange-coloured light; and the silver a beautiful yellowish green light, of considerable intensity. The light proceeding from the copper, is of a much deeper orange than that from gold, but the brass yields scarcely any light whatever.

If such a series of wires were to be exploded between cards, those cards would be stained by different colours: and you will observe, by a few experiments, that whatever be the character of the wire, the deepest stain on the cards between which it was placed is precisely in its own direction: and that the intensity of the stain becomes more and more attenuated from the axis of the discharge to the margin of the cards. Moreover, by a close examination of those cards, especially those between which brass, silver, or gold were exploded, you will perceive that a complete gutter is made in each card, directly opposite to the axis of the discharge, or the direction of the wire.

The stain made by brass is nearly black, and the figure is much in resemblance of a caterpillar. That from silver is of a greyish colour, and much scattered; gold yields a purple or violet coloured stain, much scattered, and the tints beautifully blended. Iron and platinum give no very striking colours, nor do they stain the cards to any great extent. They seem to be fused into a train of minute globules, which are left on the cards in the directions of the original wires. When iron wire is exploded between two pieces of glass, a series of minute globules of iron are firmly fixed on the surfaces of each piece, and stand very prominently above the surface of the glass.

On Electro-Gilding.-By Professor DE LA RIVE, of Geneva.*

Having long observed the baneful effects of the mercury employed in the ordinary mode of gilding, it occurred to me that the decomposing powers of an electric current, when applied to a solution of gold, might, by bringing that metal gradually upon the surface of the object to the gilt, be substituted, in many cases, if not in all, in the place of the mercury; and it is now fifteen years ago since I first made experiments on this inquiry. These first trials, however, not being successful, I dropped the investigation for the time. The progress which, since that time, has been made in electricity, and especially the discoveries of M. Becquerel, have induced me to resume the inquiry, and conduct my experiments in a somewhat different manner to those I had previously made: and I am persuaded that although I may not have arrived at perfection, I have obtained some very interesting results; which in the hands of the experienced artizan, may become universally advantageous in this branch of employment."

The principles by which I have been guided in this application of the decomposing power of the electric current to the gilding metals, are the following::

1st. The employment of feeble electric powers to effect decomposition when we wish to obtain a regular and uniform deposit of the particles of gold liberated from the solution, which is a chloride of that metal.

2nd. The employment of a bladder to keep separate the two liquids, placed one after the other, in the same electric circuit, and prevent their admixture whilst the electric current traversed them in succession. One of these is a solution of the muriate of gold, the other, water slightly acidulated, and in which the zinc piece is immersed.

3rd. The third principle is that which the electric current possesses, of passing with the greatest facility from a liquid to a metal, and vice versa, when the metal is most susceptible of being chemically attacked by the liquid. In the present case, the metal immersed in the solution of gold, is more easily attacked by the liquid than the gold itself; from which it follows, that the whole of the immersed part will not be completely gilt. The current, however, will seek the points where the metal is still bare, to traverse them and deposit gold on them, whatever may be the length of the route it has to pursue in the liquid, or however irregular and complicated may be the surface of the object intended to be gilt.

The following is the mode by which I have been enabled to apply the three preceding principles to gilding; the first two are due to

This is the paper alluded to by the author in his paper on the same subject, given at p. 216 of this volume.-EDIT.