manner, I make the other, of copper, communicate with the superior disc of the condenser, whilst the interior disc communicates, as it ought, with the ground. A moment afterwards, raising this upper disc into the air, and holding it insulated, it gives me by the electrometer from two to three degrees of negative electricity (el. -), accordingly, as such a condenser condenses from 120 to 180 times. This proves that the electric tension of the above-mentioned plate was about a sixtieth of a degree, or nearly equal to that which the two plates of copper and of zinc acquired in the preceding experiments, when applied to each other by the whole extent of their flat surfaces. When we reverse the experiment, that is to say, when we cause the plate of zinc to communicate with the condenser, we likewise obtain from two to three degrees, but of positive electricity (el. +). However, if the disc of the condenser be copper, and the zinc touch it immediately without any intervening substance, we obtain nothing, because the zinc being then in contact, at the two opposite ends, with copper and copper, two equal forces act in opposite directions, and by that means destroy or counterbalance each other. It is, therefore, necessary that the communication of the plate of zinc with the copper disc of the condenser should be effected by the interposition of a conductor, which should be a simple conductor merely, a humid conductor, such as a piece of wet card or cloth. As to the rest, the action which excites and gives motion to the electric fluid does not exert itself, as has been erroneously thought, at the contact of the wet substance with the metal, where it exerts so very small an action, that it may be disregarded in comparison with that which takes place, as all my experiments prove, at the place of contact of different metals with each other. Consequently the true element of my electromotive apparatus, of the pile, of cups, and others that may be constructed according to the same principles, is the simple metallic couple, or pair, composed of two different metals, and not a moist substance applied to a metallic one, or inclosed between two different metals, as most philosophers have pretended. The humid strata employed in these complicated apparatus are applied, therefore, for no other purpose than to effect a mutual communication between all the metallic pairs, each to each, ranged in such a manner as to impel the electric fluid in one direction, or in order to make them communicate, so that there may be no action in a direction contrary to the others. After having well ascertained the degree of electricity which I obtain from one single pair of these metallic pieces, as shown by the condenser which I employ, I proceed to show that with two, three, four pairs, &c., properly arranged, that is to say, disposed all in the same direction, and communicating the one with the other, by as many humid strata (which are necessary, in order that there may be no contrary actions, as I have already shown), we have exactly the double, triple, quadruple, &c., so that if with a single pair we should be able to electrify the condenser to that point as to make it indicate, by the electrometer, three degrees, for example, we should obtain six with two, nine with three, twelve with four, &c., if not exactly, yet nearly so. You have seen these experiments, and have appeared to be very well satisfied with them, as well as M. Pictet, who seemed enchanted with them, and was never tired with seeing them repeated. Here then we have already constructed a small pile, which however does not yet afford any indications by the electrometer without the aid of the condenser. In order that it may immediately afford these, in order that it may arrive at one whole degree of electric tension, which it will scarcely be possible to distinguish, because it amounts to no more than half a line on the electrometer, it is necessary that such a pile should be composed of about sixty of these combinations of copper and zinc, or, which is better, of silver and zinc, on account of the sixtieth of a degree which each combination yields, as I have already remarked. It then also affords shocks if we touch its two extremities with wet fingers, and much stronger shocks if we touch them with metals grasped by large surfaces in the hands, well moistened, by which means a much better communication is established. In this manner we may receive shocks from an apparatus, whether in pile or with cups, of thirty and even of twenty pairs, provided the metals be sufficiently clean, and especially if the humid strata be moistened, not with mere pure water, but with a considerably strong saline solution. These saline liquids, however, do not properly augment the electric force-not at all-they merely facilitate the passage, and leave a freer course for the electric fluid, being much better conductors than simple water, as several other experiments prove. In order to establish this fact, and render it evident to such as have found a difficulty in admitting it, that the electric force or tension is, if not entirely, yet very nearly the same, whether the wet layers be moistened with pure water or with a saline solution, though the difference in the shock is so great, I have frequently made the following experiments, of which I have spoken to you, and which I would have shown to you, if I had been provided with the requisite articles. I take thirty cups or drinking glasses, with which I construct one of these apparatuses which I term a crown of cups, putting into them a sufficient quantity of pure water, and causing them to communicate, the first with the second, the second with the third, and so on successively to the last, by means of metallic wires, which terminate at one end in a plate of copper, and at the other in one of zinc, and are all turned in the same direction. The apparatus being constructed in this manner, I try its electric force, by causing the first of the cups to communicate with the ground, and applying the condenser to a piece of metal which is partly immersed in the last this condenser, when I afterwards withdraw it, and separate one of its discs from the other in the proper manner, and without delay, gives me forty, sixty degrees, and more, according to its condensing force. I also try the shock in the most advantageous manner, and find that it is very slight: after having well ascertained both the degree of the electricity and the weakness of the shock, I add a pinch of salt to each cup, and repeating the proofs, I find that the electricity has not been at all increased, the condenser giving me still only forty or sixty degrees, as before: but the shocks are incomparably stronger. There are many other experiments which I have described to you verbally, and which I would willingly have performed before you, had I not been in want of the requisite apparatus. I informed you -at which you were much astonished, and M. Pictet still more so --that with one apparatus I charge a Leyden phial, whatever its capacity may be, and even a large battery; that I charge them in an instant, or to speak more accurately, in less than a twentieth part of a second, and almost to the same degree as the apparatus itself, namely, to about one degree of tension, if the apparatus be composed of sixty pairs; to two degrees if it contain one hundred and twenty, &c. ;—that I am then able to draw, by the help of the condenser, a strong spark from a small jar charged in this manner, a great number of similar sparks from a large jar, and almost without limit from batteries, as I am actually able to draw them without limit of number from the apparatus itself. I have informed you that large bottles charged in this manner gave me moderate shocks, and batteries pretty strong ones, as high as the elbow and higher; that the shocks of a battery of ten square feet of coating, and charged in less than a twentieth part of a second by one of my apparatuses, of two hundred metallic pairs, are very violent and almost insupportable; for I have not yet made any trial with larger batteries; but that there is every probability that the violence of the shocks increases with the size of the batteries, as far as a certain term, which I am not able to define; so that it would be possible, with batteries of 40, 60, and 100 square feet, to give considerably strong shocks, by charging them by the transient contact of a pile only 60, 40, 30, or still fewer pairs. I have explained to you the manner in which one ought to proceed in order to perform these experiments with success; that it is particularly necessary we should carefully avoid the slightest interruptions in the communications of the conductors with the coatings of the bottles, and between each other, and that this becomes still more necessary when the electromotive apparatus, being composed of a small number of pairs, possesses but little power, so as to be unable to overcome the slightest obstacle that might oppose the passage and the course of the electric fluid. Lastly, I remarked to you that these experiments confirm in a very evident manner what all the others already suggested, namely, that the quantity of electric fluid set in motion by my apparatus is much larger for every moment of time than that which is set in mo tion by the ordinary electrical machines; that the former afford it in much greater abundance than the latter, when the object is to produce, not an accumulation of electric fluid in insulated bodies, in order to raise the electricity to a high degree of tension, which may be done with those machines, but by no means with piles and other similar apparatuses, unless we also employ condensers; but where we require a constant current of this fluid, supported by a continued action of a circle of condensers not insulated; nay, one of my apparatuses, of only sixty or thirty metallic pairs, pours out in every instant, or in any given time, more electric fluid, if it meets with no obstacle, or if the fluid be not obstructed by the too small capacity of the recipient into which it is infused, than one of the most active electrical machines with cylinders or plates of glass. In fact, where shall we find a machine capable of charging a very large battery, to one, or even half a degree, in less than an eighth of a second, of pouring into it a sufficient quantity of electric fluid to enable us afterwards to draw from it, by the condenser, a great number of sparks in succession, as is done by one of the abovementioned apparatuses ?* The other experiments, which I was able to show you in part, relate to the different electroscopic phenomena which the apparatus presents, accordingly as the one or the other of its extremities communicates with the ground, or both of them, or neither one nor the other, or as they communicate only between themselves and with the ground at the same time; accordingly as these communications are effected by perfect conductors, conductors more or less imperfect, &c., all which circumstances singularly modify and produce great variations in the results, which often appear curious and even anomalous, but which, nevertheless, I think myself able to explain in a satisfactory manner, without deviating from my principles and sound electrical theory, attention being paid to the mode in which the imperfect or bad conductors act. It would carry me too far to enter at present into these details; what you have already seen, and what I have communicated, may be sufficient for the present occasion. [The electricity developed by the simple contact of bodies, was first discovered by the Rev. Abraham Bennet, prior to the year 1789. This ingenious philosopher, who is also the inventor of the electrical doubler, has published an extensive series of experiments on the contact of metals; which, although not introduced in the proper chronological order in this historical sketch, shall be made known to our readers before we quit the subject.-EDIT.] • On this subject see Philosophical Journal, 4to, IV, 243–245. EXPERIMENTS ON THE ACTIVITY OF A GALVANIC PILE. BY M. * DYCKHOFF. In some observations of Mr. Ritter on galvanic actions, he has stated that all those substances which are placed between the metallic elements of the pile, are active in exciting electricity only in consequence of their containing moisture; and asserts that it is impossible to construct an active galvanic pile independently of wet substances. I take the liberty of placing in opposition to this doctrine, the following novel facts : : I constructed a pile with discs of copper and zinc, and small pieces of thin green glass about the size of a lentil, three of which I placed at equal distances from one another, in each interval between the metallic pairs; by which means I had as many thin strata of air, instead of moist substances, in every metallic interval in the pile. The following results were obtained by this apparatus : 1. A pile of ten pairs, assisted by the condenser, affected the electrometer as powerfully as it was affected by a wet pile of five pairs, of the ordinary construction. 2. The action continued without variation, during the time the air remained quite dry; but damp air appeared unfavourable to the electricity of the pile. 3. The same degree of electric action as that shown by the pile alone, was communicated to a Leyden jar. The plates were only three inches diameter; and as they had previously been employed in a pile of the ordinary kind, and were much corroded by the liquid, I took off the oxide with a file. The plates, however, still remained rough and uneven on their surfaces, which was probably the reason of my not obtaining a higher degree of electric action. I have not hitherto had an opportunity of carrying on the experiments on a large scale, but the results already obtained are, of themselves, of sufficient importance to place the views of Ritter in a questionable position, at least. For my own part, I can see no reason why glass, thin films of sealing-wax, and other similar substances, should not have the same influence in the pile of Volta as in his condenser. In order to ensure success in the experiments I have already described, it is necessary that the bits of glass be as thin and smooth as is possible to procure them; for if the film of air be too thick, it is natural to suppose, that the feeble electricity excited by the simple contact of the metals, would be too insignificant to affect the adjacent metallic pairs in a degree sufficiently active to become conspicuous. [The next form of the dry electric pile was made by M. Marechaux, in the year 1806, as will be understood by the author's own description of it in the following paper.-EDIT.] Voigt's Magazin fuer den neuvesten Zustand der Naturkunds, vol. iv, p. 791. + Intellegenzblatt der Allgemein litteraturzeitung, 1802, No. 193. |