it being only where we have negative clouds relatively that we can have thunder-storms. Still, these positive clouds discharge their electricity. This discharge is continually taking place, and in much greater degree when unseen than when observable by the human eye. During fog, and rain, and snow, it descends on the particles of those bodies; but, when the air is dry, and, consequently clear, the attraction of the earth causes the electricity to be discharged from the clouds; but, the air being a bad conductor of this agent, it is rendered visible to the eye in its descent to the earth, and it is only when it is drawn from the upper regions that it is visible: when it comes near the earth, it becomes so diffused that the eye loses it. We have thus the phenomenon of aurora borealis and australis, as the same causes exist at the other pole. There are a

multitude of observed facts that all tend to prove this, and it would be somewhat difficult to ascribe it to any other cause, if we take into consideration that clouds are bodies, under all circumstances, charged with electricity.

ELEMENTARY LECTURES ON ELECTRICITY, &c.

LECTURE XV.

In pointing out the particulars to be attended to in the employment of the electrical battery, I shall, in the first place, observe, that if the battery be charged to a high degree of intensity, and discharged in the usual way of discharging single jars, and especially if the circuit between the inner and outer surfaces be short, one, or more, of the jars is almost sure to be broken, and the battery, consequently, so far spoiled; and it cannot be charged again until the broken jar, or jars, be removed. Thence the necessity of watching, carefully, the progress of the charge, so that we may make the discharge before the intensity gets too high. To prevent accident, by inattentton or otherwise from too high a charge, Mr. Cuthbertson invented a discharging electrometer, by means of which the battery will discharge itself at any required intensity, without depending on the attention of the operator.

P

Figure 3 is a representation of Cuthbertson's discharging electrometer. It consists of a stout mahogany board as a base, from which rise two glass C pillars, one of which is rather stout and the other only slender; the latter is surmounted with a brass ball, into which is screwed one end of a stout brass wire, to which the outside of the battery, either directly or indirectly, is to be connected. The other glass pillar carries vertically a wide brass tube, terminated at

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each end by a hollow brass ball, into the lower part of which is inserted, and firmly cemented, the upper end of the supporting brass pillar; and into one side of that brass ball is screwed a horizontal brass tube or stout wire, bent upwards near the outer end, and terminated by a brass ball, as seen in the figure. Through the middle of the upper large brass ball passes a horizontal brass rod, terminating by a ball at each extremity. This rod is nicely balanced on a knife-edged fulcrum in the interior of the large hollow brass ball; and the arm which projects over the lower bent arm is graduated, and finished with a sliding weight, which, when placed at different distances from the fulcrum, loads the arm with a proportionate weight, from one grain to sixty grains. The ball of the graduated arm of the balance rests upon the ball of the lower bent arm. The ball at the other end of the balance will then be four inches from the other ball which surmounts the slender glass pillar. If, now, the metallic part of the instrument, supported by the stout brass pillar, be connected with the prime conductor, or the interior of the battery, then, while the latter is discharging there will be a repulsion between the ball of the bent arm and that of the balance which rests on it; and, at the same time, an attraction will take place between the other two balls; and when these repulsive and attractive forces overcome the weight at the other end of the balance, the attracted arm will descend, and discharge the battery on the lower insulated ball. Now, as the attractive and repulsive forces will always be proportional to the intensity of the charge, and as these forces have to overcome the load at the other end of the balance, that load, whatever it may be, is a proper measure of the intensity of the charge. The instrument is usually surmounted by a quadrant and electrometer, as shewn in the figure, as an indicator of the progress of the charge, which is not shewn by the discharging electrometer itself.

It is obvious, from a consideration of the beautiful arrangement of the various parts of this instrument, of the principles upon which it operates, and of its functions as a self-discharger at any required intensity, that it is well calculated to relieve the anxiety, and dispense with much of that attention of the experimenter, which he invariably labours under by the employment of the ordinary discharging-rod alone; for the sliding weight being once adjusted on the horizontal arm, for any given intensity, and the body to be operated on properly placed in the circuit, the experimenter's care is at an end, as the machine has (now) only to be worked till the discharge takes place.

The mechanical action from a discharge of an extensive battery of jars is exceedingly great, and bodies of every kind, whether conductors or nonconductors, can be perforated, torn, or even shattered to pieces by means of it. If, for instance, we now place a quire of paper vertically between the two balls of the universal discharger, and arrange this apparatus so as to bring the paper into the circuit of the battery when charged to about 80° or more, per quadrant

electrometer; the electric fluid rushes with violence through the quire, and tears the outer leaves to a considerable extent, whilst the inner ones are sometimes partly torn, but more frequently perforated in several places. Several thick cards may also be torn in a strange manner by a discharge from the battery; and if the paper or cards be made slightly damp, the ruptures made by a discharge are frequently much greater than when operated on in a dry state; and as the moisture communicated to them enhances their electric conduction, a greater number of plies can be perforated when so treated.

The electro-mechanical and electro-calorific effects are sometimes so intimately connected with each other, that it would be impossible to separate them by any mode of experimenting hitherto known. For, although there be some singular exceptions to the general rule, it generally happens that the greater the mechanical action the more favourable is a discharge in accomplishing the ignition of bodies through which it is transmitted.

Let us, for instance, employ the force of a single jar, when charged to a high intensity, upon a narrow strip of gold leaf placed between two dry cards. The whole of the circuit, I should wish you to observe, is of good conducting materials-metals. Now, the discharge being made, we examine the result on the strip of the gold leaf, and find that the metal has entirely disappeared; but both cards are stained with a beautiful purple or violet-coloured tint, very curiously distributed, and extending over nearly the whole of the two inner surfaces of the two cards, being most dense, and of the deepest colour along the middle, where the gold leaf was placed, and becoming more and more attenuated thence to the outermost skirts of the stain.

Now, by paying attention to the complicated results of this experiment, we first discover that the metal is destroyed, or, in fact, deflagrated, and thus, by oxydation, has assumed a different colour: and we next observe that the mechanical action has distributed this oxyde over a much larger space than the gold originally occupied. And what is particularly remarkable, these mechanical effects are chiefly produced laterally, and but very little, if any, are to be observed longitudinally, or in the direction of the discharge. I shall, however, as we proceed, endeavour to vary this experiment, and shew the effects by different arrangements of the apparatus. At present, I offer to your notice but one or two variations, which will be sufficient to convince you that when the electro-mechanical action is sufficiently abated, the gold leaf suffers no change, even from the most formidable electrical charge that we are capable of producing. The experiment by which I am about to prove this fact, will differ

As there are scarcely two of these electrometers which give the same indications for any given intensity, 80° will not express the requisite intensity with different electrometers; I should, therefore, wish it to be understood, that as the mechanical effects depend more on the intensity than on the quantity of fluid employed, the intensity for purposes of this kind should always be considerable.

in no other respect from the last one, than by the introduction of an inferior conductor to the circuit whilst discharging the jar. The inferior conductor which I employ for this purpose is simply a piece of wet thread, about eight or ten inches long: it forms a part of the circuit, and will be the means of lessening the mechanical action, and you will observe that, by this arrangement, the gold leaf remains uninjured by the discharge of the jar through it, although the intensity of the charge was as great as in the former experiment.

As it is still possible that you may require further evidence respecting an abatement of the mechanical action by such an arrangement as that last employed, I will again vary the experiment, to convince you of this fact, and to shew you that the calorific effects on the gold have a dependence on the electro-mechanical action in the manner I have already stated.

In this variation of the experiment I will make a slight opening in the metallic part of the circuit, and in that opening I will place some light seeds, which, as you already know, would be blown away were I to discharge the jar through them when the rest of the circuit is metallic but now, as the discharge has to pass through the inferior conducting wet thread, you will find that the seeds remain almost unmolested; they are not scattered abroad, as before, and the only disturbance which they experience is a mere consequence of some trifling attraction which takes place between them and the ends of the wires where the metal circuit is interrupted. The gold leaf, you will observe, is not in the least changed.

We might now vary the experiment in another manner, by dispensing with the wet string, and making the whole circuit metallic, with the exception of a small opening where small seeds may be placed, as in the last experiment. Now, in this case, we have a fair opportunity of comparing the mechanical action on the seeds, with that of the last trial; and you will find that the seeds are blown away, and the gold leaf is destroyed.

I know of no experiments by means of which I could shew you that the calorific effects on the gold depend on the electro-mechanical action of the discharge.

However, I have still one other variation of the experiment, which I shall now proceed with. You are aware, that when a jar is discharged, in the usual way, through any person, a violent shock is produced; but if I place the wet thread in the circuit, no shock whatever is experienced. Now, by placing myself, the wet thread, and the gold leaf in the circuit, I discharge the jar from a high intensity, without producing any effect either on the gold leaf or on myself.

Description of a Voltaic Battery, in a Letter to the Editor from Mr. E. WENCHEBACT.

Amsterdam, 16th. Feb., 1842. Sir, The Annals of Electricity, Magnetism, and Chemistry for December, 1841, contains the offer of a prize volume for a voltaic

battery that "will decompose acidulated water at a greater rate, and with less cost, than by any hitherto made public. The time of action not to be less than four hours."

I now take the liberty of addressing you a few lines, for the purpose of stating that the effects of a battery invented by a friend of mine, are able to answer to the above-mentioned question. Not exactly knowing what quantity of decomposed water already has been obtained in your country, and therefore not being able to make any comparisons between them, I will at once submit his results to your more perfect knowledge, and shall be highly obliged if the trouble I am now making to you, can be rewarded by the results themselves.

To W. Sturgeon, Esq., Royal Victoria Gallery, Manchester.

The battery in question consists of 10 jars, each of which is constructed by an ordinary vase or vessel, wherein a cylinder of amalgamated zinc ( of an inch thick) is placed, and fit for receiving a porous diaphragm of earthenware with a piece of coke in it. The coke and zinc are connected together by a thick copper wire, soldered to the zinc, and in full contact to the coke by means of a hole filled up with mercury. The coke being of a very irregular form, it is somewhat difficult to ascertain its surface accurately, but from estimate I think it certainly does not exceed 300 square inches (English) by the whole battery. The room between the coke and earthenware is filled by acidum nitricum, whilst the zinc cylinders are placed in water with a few drops of sulphuric acid in it. The same effect will be produced when the room is filled by sand, and the liquids thrown upon this till the sand becomes quite wet. last method, certainly, is the more economical.

The

The decomposition of water goes on at a rate of 384 cubic inches in four hours, without the least interruption, the action of this battery being so constant, that Prof. Van du Boon Mesch, at Leyden, to whom one of the jars has been sent, ascertained that its action, though with less vigour, continued for eleven days.

The consumption of zinc is very small, and the evaporation of nitric acid only takes place when the poles are connected. All the other effects of heating, burning charcoal, lighting, &c., are very strong, and equally gratifying when first tried. The only remark which is to be made is, that notwithstanding every piece of coke will have the same effect, the sort which is known by the name of carbon is the most fit for the purpose, because it is more tight, and not so very hard that a carpenter should not be able to bring it into a regular form by means of a saw.

Certainly many persons will apply for competition, and perhaps some of them may still have been more successful than my friend; should that be the case, cast this letter aside, and only when you think it fit for competition or publication in the Annals, you will highly oblige my friend, whose name I am ready to make known to you when admitted for competition, and as soon as you will do me the favour of a few lines in answer to my undermentioned address.