THE ANNALS OF ELECTRICITY, MAGNETISM, AND CHEMISTRY; AND GUARDIAN OF EXPERIMENTAL SCIENCE. JULY, 1842. On the Electric Column and Aerial Electroscope. By J. A. DE LUC, Esq., F. R. S. (Continued from page 454, vol. viii). ARTICLE I. THE principal result of my paper on the Analysis of the Galvanic Pile, has been to show that by this instrument, in which Sig. Volta has so much extended Sig. Galvani's first discovery of some physiological effects produced by two associated metals, we have been really enabled to determine whence proceeded that action upon the animal economy. When these effects were discovered by Sig. Galvani, appearing similar to the shock produced by the Leyden vial, they pointed out some action of the electric fluid; but when this fluid acts thus upon our organs, it is also manifested by electric motions and by sparks; whereas not even the first of these signs appeared in the galvanic experiments. Therefore the action of the electric fluid in these first phenomena might for ever have remained doubtful, had not Sig. Volta, by the invention of his admirable pile, increased that action, so as not only to be attended with electric motions and sparks, but to produce some chemical effects known before to belong to the electric fluid. But there remained a great question. These different effects had before been produced by the electric fluid only when it was arrived at a great density; while the pile produces the same effects with so small a quantity of the fluid, as to be often hardly sufficient to move the gold leaf electroscope. This has been the object of the experiments contained in my first paper, which have manifested two distinct effects in the pile: 1. A motion of the electric fluid produced by the association of two proper metals, independent of any other effect: 2. A modification of this small quantity of electric fluid, on pervading the pile during the calcination of some of Ann. of Elec. Vol. IX. No. 49, July, 1842. its metals. A distinction first shown by different dissections of the pile, and afterwards directly proved, by producing an instrument, which retains the electric effects of the pile by the association of two metals, without either its chemical effects, or the shock. This new instrument was to be distinguished from the galvanic (or voltaic) pile; therefore, in my second paper delivered to the Royal Society on this subject, I named it electric column, as being a spontaneous and permanent electric machine; and it manifested also, by changes in its electroscopes, some variable influence of the electric state of the air, this new effect was to be expressed by an additional name. It is different from the indications of our former atmospheric electroscopes, such as elevated conductors and kites, which inform us only of the comparative states of the stratum of air that they attain, and of the air at the place of observation; without any indication of the changes in the latter, probably connected with some phenomena which we observe, without knowing their cause; and as the electric column seemed to promise a method of discovering these changes, I named it also aerial electroscope. Such had been the principal object of my second paper presented to the Royal Society; it was only in its nascent state; but as I thought it worthy to be taken up and followed by other experimental philosophers, I would not postpone communicating it to the public till it was more advanced; it has not been published in the Phil. Trans., and as I have since carried it further, I shall here treat it in a different manner, dividing it into three parts; the first will relate to the electric column, considered only as the electric efficiency in the pile, divested of either chemical or physiological effects. The second will explain the difficulties which I have encountered in attempting to bring the instrument to its desirable function as an aerial electroscope, and the point which I have attained in this new kind of meteorological observations. And in the third, I shall offer to the attention of the natural philosopher, some meteorological observations, which show the importance, in every branch of experimental philosophy, and especially in chemical theories, of forwarding the observation of atmospheric phenomena. PART I. On the Electric Column. I have explained in the first paper, my hypothesis concerning the cause of a motion of the electric fluid, produced by the properties of two associated metals; and as all the circumstances attending this motion are characteristic of its cause, this connexion will be here my principal object. I shall begin by some experiments previously mentioned, in which brass tripods were placed between the two these groups separated by pieces of wet cloth. dissection of the pile, both electric and chemical metals, and In this first effects were produced, the latter on account of the water contained in the cloth; and I wanted to know what would be the consequence, in the same arrangement, with respect to the electric effects of suppressing the chemical ones, by a dry intermediary substance. For this purpose I substituted for the silver plates and the wet cloth of the former experiment, pieces of Dutch gilt paper, placing the brass tripods between the zinc plates and the copper side of the papers; and after having found, that forty such groups could be contained in each column of the frame described in that paper, forming in the whole eighty groups, I made the following experiments. Experiment 1. In order to judge what would be the effect of interposing the brass tripods between the metals, I first mounted the eighty groups without them, and observed the degree of divergence of the gold leaves at both extremities. Dry paper not being so good a conductor as wet cloth, the electric effects were not so great as they would have been with the latter; but they were sufficient for my purpose. I kept this apparatus for some days, observing the divergences in different parts of the day, and the greatest, which happened to be at the zinc side, was of 0.3 of an inch. Exp. 2. I then placed the brass tripods between each zinc plate and the copper side of the papers, the paper side of which separated the binary groups of metals, as did the wet cloth in the former experiment: the electric effects remained the same as they were in Exp. 1, without the tripods. It came then into my mind, that the tripods, being of brass, might alone produce some effect, with only plain paper to separate these groups of zinc and brass; but the latter having but a small mass, the transmission of electric fluid along the column could not but be slower; and this was the very reason which determined me to the trial, as an experiment that would also relate to the cause which renders the column an aerial electroscope: this cause is the action of the ambient air, the immediate effects of which are, to lessen the positive state of one of the extremities, and the negative state of the other, according to its own electric state; and more slowness in the motion of the fluid giving more time to this action of the ambient air for diminishing the electric indications at the extremities of the column, these symptoms were to be smaller. This therefore induced me to make the following experiment. Exp. 3. I mounted the column with eighty groups composed of zinc plates with only the brass tripods, separating them with pieces of writing paper, and I kept also this column for some days, observing the electroscopes at its extremities: they had the same variations which I had before observed, but very small, and the greatest divergence, which, as it is commonly, was in the middle of the day, did not exceed 0.1 of an inch. I now come to that slowness mentioned above in the motion of the electric fluid produced by the property of the column, which being attributed to a fluid known to possess, in the proper sense, the swiftness of lightning, must appear a paradox. Rapidity of motion certainly belongs to the electric fluid, when darting in a torrent; but the electric matter, of which it is composed, has a tendency to adhere to all bodies, air included; and it is this very property, as explained by Sig. Volta, which occasions the electric motions, when the fluid, tending to move by a rupture of its equilibrium, is more reluctant to be separated from the body which possesses it, than the latter to follow the fluid in its motion. The effect of this tendency of the electric fluid towards bodies, in retarding its motion within the column, is analagous to an effect observed in water. When water is kept in motion in a channel by a constant supply, it is seen to take its course in the middle, leaving behind the particles retarded by their tendency towards the sides, which is decreasing as the distance increases. But the analogy is more direct, when water is confined in a pond, beset with aquatic plants or other impediments; for the motions impressed on that water at one side of the pond, though continued, if small, are but slowly and seldom completely communicated through the whole space. The case is the same with respect to the electric fluid set in motion by the property of the column, not only when confined within it, but when a current is produced; which effect will be shown by some experiments, after I shall have explained some parts of the figure annexed to this paper. See Plate I.* The dimensions of this figure are half those of the original: it consists of many parts which I shall successively describe, beginning by those which relate to my present object; its fundamental parts are an electric column, with its electroscopes. The former is represented at A, B, supported horizontally on two pillars 1, 1, consisting of solid glass rods, covered with sealing wax, or with some other insulating varnish, and fastened on the wooden base 2, 2, by female screws underneath. The column itself is composed of 600 groups, formed of zinc plates 0.7 inch diameter, and equal pieces of plain Dutch gilt paper; the copper side of which being turned towards A, this is the positive extremity of the column; and as also, in every group, the paper itself serves only to separate the binary groups of zinc and copper, the latter being in each of them on the side of B, this is the negative extremity. The groups are contained between three glass rods, covered with sealing wax melted over them while hot, and fixed in holes of the brass plates A, B, where they have been introduced while the plates were hot, and the holes filled with sealing wax. These brass plates have in their lower part a pin, which enters freely into the brass cap at the top of the pillars 1, 1. At the extremities of the column are screws 3, 3, formed on the outside in the shape of loops; they serve first, to press the groups between the glass rods; and besides to produce, by brass wires hooked in their loops, the communication of each extremity with the nearest electroscope, as represented in the figure. • Plate I could not be got ready in time to appear with this number.-EDIT. In general this column produces too great effects for the experiments which I have here in view, as the gold leaves strike the sides of the electroscopes; while there should be merely a simple divergence therefore, either a smaller column must be used, or the time must be chosen when the 600 groups produce only this effect. Exp. 4. Having observed the actual quantity of divergence in both electroscopes, when I lay my finger on the top of either of them, in order to produce the communication of its extremity of the column with the ground, the divergence ceases in it, and becomes nearly double in the other. Then taking off my finger, and thus abandoning the column to its own operation, the divergences are not immediately restored to their former quantity; it requires some time to produce them again, even half an hour or an hour. This shows a reluctance in the parts once possessed of the electric fluid, to obey the cause which requires more of it on zinc than on copper, in order to establish the equilibrium between them. But this concerns only the quantity of electric fluid, which the column possesses in common with the surrounding bodies and the ambient air; for at the same time that this quantity delays to obey the law of the column, if an insulated body, either positive or negative, but in a degree which can merely affect the gold leaf electroscope, be applied to one extremity, the effect is instantly perceived at the other. This again is the same as if a stream of water were introduced at one side of the pond of the above example, and an opening made at the opposite side; for a current would be directly produced through the pond. Exp. 5. After having disturbed the state of the divergences at the extremities of the column, by placing a finger on one of them, the mode of reproducing speedily the former state is, to lay the fingers on both extremities together, and remove them at the same instant if this last condition be really obtained (which is not easy) the original divergences are restored. These experiments cannot leave any doubt, that the phenomena of the column, as well as the electric part of those of the pile, are produced by a fluid set in motion. Exp. 6. In the same case as that of the above experiments, namely, when the divergences are not too great, if one side of the column be placed in communication with the ground, the effects of the contact on the other side are so similar to those produced in the same manner on the leaves of the mimosa sensitiva, that this conformity of effects seems to indicate some analogy between the causes: both contacts make the leaves fall; they rise again, but it requires some time. There is an objection against the idea that the phenomenon of the plant is electric; because in the column the same effect is produced, at one side by imparting, and at the other by taking off, some electric fluid. This objection however is not absolute, for we do not know all the actions of organic bodies on the electric fluid; but if it is not this, it must be some other fluid, |
