far the most important point, that a minute battery may be compelled to give forth tremendous quantities of machine-electricity. The grand step hitherto taken in this investigation, we believe, was that of Dr. Faraday, in the discovery of magnetic induction in secondary coils, which, as we shall shew, strikingly resemble the water-battery in more respects than one. It occurred to the writer, that with so vast an intensity as the induced current possesses, it would be capable of carrying a considerable amount of the fluid along a very slender wire, even if that wire possessed feeble conducting powers, This would bring the coils into a much smaller space round the magnet, and of course very considerably increase the effect. On trial, this was found to be correct; the fine iron wire, which is used for artificial flowers, covered with cotton, and wound off on reels of half a pound, may be purchased at most of the wireworkers for fifteen-pence a reel. Half a pound of No. 30, copper wire so covered, measures about 400 feet, and costs at the opticians 4s. 3d. ; ten yards of the insulated copper wire balance 35 yards of the covered iron; therefore the half pound of iron wire measures about 1,200 feet, and a given length of it is nearly twelve times as cheap as the copper wire hitherto used for secondary coils. To opticians themselves, the saving will be about 5-6ths of what they have ordinarily spent on the fine copper helices; and hence we may justly conclude, that iron will very soon supersede copper wire altogether for giving shocks and effecting decompositions. On trying a moderate length of each, made to slide over an electro-magnet, the power was very nearly equal; but with two coils 1,200 feet long, the iron was the more powerful. These coils have been examined and approved by Mr. Watkins, whose urbanity and electrical skill are known to many, and who will supply any person desirous of it, either with the machines so made, or the materials for their manufacture, at a moderate cost. The iron wire will be found to have a twisted joint once in every thirty or forty yards, which must be cut off, retwisted with a pair of pliers, and insulated with sealing-wax over the flame of a candle, or rather under, for the blue flame answers best. One great advantage now obtained is, that experiments on secondary coils may be followed out without the heavy expense formerly attending them. To shew that soldering is unnecessary in the secondary coil, we attached to it two pieces of brass chain, containing 5,230 links in all; and by the tension of gravity alone, the connections were sufficiently good to communicate shocks without any great diminution of strength. On closing the circuit with about 400 links, and shaking them, illuminating sparks ran along the chain with a very pretty effect. We observed these sparks still to exist when the chain was fastened to one end only, and by merely applying gently, a blunt-pointed wire to each binding screw in succession, found that sparks were observable from both, but came brightly from one, and feebly from the other. This we at first attributed to conduction up the leg of the table, but subsequent experiment seemed to prove that the magnetic current, like that of a water battery, will strike at a distance. On making connection, by laying a rod covered with silk ribbon, and attached to one screw, on the edge of a copper-plate touching the other, a constant flow of minute sparks passed between the metals. With a very powerful secondary coil made for the purpose with iron wire, this succeeded through four folds of dry silk, and there stopped. It might be objected that the silk, in some way served for a conductor. To determine this two copper wires 1-30 inch diameter, with the ends blunted on a hone and amalgamated, were Fig. 8. a bound, at a distance of 1-100th of a distance of an inch from each other, to a glass rod, with waxed thread, (fig. 8), as in Mr. Crosse's experiment. This was examined with a glass, and connected with the coil, when immediately a smart fire of brilliant sparks commenced between the two wires, which could be stopped and continued at pleasure: at 1-50th of an inch, the sparks appeared occasionally. It must be confessed that illumination appeared strongest close to the glass; so a notch was cut in the rod immediately under the points, leaving them quite apart from the glass, and thus throwing the conduction of the rod into the scale against us. Nevertheless at 1-100th inch, the sparks passed as before. To put all doubt away, the apparatus was placed in vacuo, which only heightened the beauty of the experiment, for now the illumination was more diffused, sometimes licking round the side of the wire, but was confined to one pole only. With a magnifying glass, the appearance was very beautiful, and the isolation of the points seen of course more distinctly. To effect this, it is only necessary to fit a tube 4 inches long, with bladder ferrules at each end by cap-cement; fasten one wire to one of the stopcocks, and coil the other into a helix of four or five turns, with bent termination to press against the stopcock at the other end. The fact is thus established, and we believe it is a new one, that the magnetic spark will strike through a vacuum, or at all events, through an atmosphere as rarefied as ordinary instruments can render it, without VOL. I.-No. 2. M contact. This important result would be more so, if it could be proved that magnetic and voltaic electricity are absolutely identical except in origin. The following simple experiment will show their similarity: three powerful secondary coils were arranged with their respective primaries; the primary of a connected with a Grove's battery and rotating magnet, the secondary of a sent its current through the primary of B, and that of B through the primary of c. The secondary of c. gave no indication of shocks, but on lacerating the tongue with a penknife and moistening it with salt, a faint shock became perceptible. Removing c, the secondary of B gave very smart shocks above the wrist. Professor Wheatstone has, we understand, occasionally used the secondary current in his experiments. As every one knows, the magnetic current is induced also in the primary itself, and forms the greatest antagonist to electro-motive schemes, yet observed. But where many and long coils are used, even this may be turned to considerable account, by connecting the two ends of such helices, but introducing into the circuit (i. e. this second circuit, independent of the battery), the decomposition to be effected, or other work to be done, and the disruptive apparatus, fig. 8.; no care need be taken that such decomposition, &c., be easier than that going on in the battery, because when the secondary current passes at all, that connection is entirely broken. In this manner duplicate magnetic effects might be produced by one battery, the latter current acting as a second generative power; or the battery might be used for rotations near at hand, and the secondary stream for signals afar off, by reason of its intensity; for such results, we should not wish the length of spark from wire to wire to be the greatest possible, but rather a minimum, or the least distance at which our present instruments will perfectly isolate their two terminal surfaces. It is very probable, also, that this application of the secondary current will tend much to neutralize its reaction on the iron; for the disruptive spark of a primary coil is much stronger when the secondary wound round it is not connected, and its enfeeblement the moment that the latter is put to other work, or connected by the wires in fig. 8, is very striking and instructive; we could wish for time to pursue this further. We should have mentioned that the apparatus in fig. 8, when the wire (a) was connected with one end of the secondary coil, and the finger laid upon (b), no connection being made with the other end of the coil, gave a stream of feeble sparks across about one two-hundredth part of an inch, when connection was repeatedly broken in the primary. This could not be owing to any completion of the circuit, for a far shorter passage would have been through or over, the four inches of wood separating the two screws. One of the terminations exhibits this with much greater vivacity than the other, which is just what we ought to expect. We would suggest to those, who, like Mr. Crosse, possess an extensive water-battery, to try this same experiment at one of the poles, without completing the circuit, and almost venture to predict the result. Here is really a considerable field for exertion; will no one push into it? It will now be understood, why, with careless manufacture, a secondary of 1,600 feet is little stronger than one of 3 or 400; for if the m-th coil touch the n-th coil too nearly, and m, n, be very distant integers, the intensity will cause the fluid to strike between them, and the effect of n-m turns of wire be wholly lost. For this reason, the first end of a secondary should come out at the side of the reel, so that the advanced coils cannot strike with it: for this reason, also, it is better to wind such helices in a lathe, for then n-m will be the least possible, and to reduce this to its lowest value a short reel should be made use of. To any person who has time it would be a very interesting attempt, to make a secondary coil insulated from the earth, and with all its coils insulated from one another by a bedding of cement, which might be effected by keeping the reel hot upon a lathe, and occasionally bathing it with melted cement, whilst the wire covered with cotton should be run upon it; perhaps a red-hot iron laid parallel, and close to the reel, would keep it hot enough. It appears quite possible that one coil thus made, should eventually be brought to afford stronger charges of frictional electricity than the water battery, and perhaps some modification of it will one day put the cylinder and plate machines out of date. We believe that what is commonly called voltaic intensity, is in reality the very opposite, or a retardation of current, and this retardation of current varies directly as the number of batteries in the circuit (vide power of heating wires); but when this retardation is very great, the stream approximates in character to frictional electricity; but if the velocity of the current from a single pair of plates be finite, then that of frictional electricity must be finite also, (which latter we know,) and the number of batteries, by which the first may be slackened into the second, finite; but if magnetic and voltaic currents be identical, and if the coils of a helix answer the purpose of batteries in a series for magnetic currents, then would a finite number of turns suffice to make the two terminations of a secondary equivalent to the positive and negative conductors of an electrical machine, or in other words, the conjecture just thrown out would be feasible. But it is high time to bring our observations to a close, which we shall do in the words of Professor Grove:* "Had it been prophesied at the close of the last century, that by the aid of an invisible, intangible, imponderable agent, man would, in the space of forty years, be able to resolve into their elements the most refractory compounds, to fuse the most intractable metals, to propel the vessel or the carriage, to imitate, without manual labour, the most costly fabrics, and, in the communication of ideas, almost to annihilate time and space;—the prophet, Cassandra-like, would have been laughed to scorn." J. E. A. U. C. POSTSCRIPT, (23rd July.)-Since this article was sent to the press, we have fallen upon a memoir in the Philosophical Transactions, by J. P. Gassiot, Esq. F. R S., of the existence of which we were not aware. In this able paper, he gives the results of experiments in which secondary coils of very great length were employed; and the primary current was induced by a series of twenty of Mr. Daniell's largest batteries. The results however, though developed with an accuracy to which we make no pretension, by means of a micrometer, do not appear to have been greater than our own. Throughout our experiments we invariably used small batteries, on the constructions of Messrs. Grove & Smee; and sometimes the negative plate was only two inches square. We may also state that we have used iron secondaries for upwards of five months. Lastly, it will be useful to some to learn, that a continued use of platinized lead induces us to give it an average rank as to power, somewhat below platinized silver, and we find that it requires the platinization to be repeated periodically. 1. THE STORY OF THE FALCON. FROM BOCCACCIO. 1. FAIR Florence, queen of art and poesy! II. 'Twas on a day in June, a cloudless sky When all apparelled in gay finery, Her citizens in little crowds repair, Unto the Alberighi Palace where In haste, each anxious to be first they went To see the glories of the tournament. * Lecture on the progress of Physical Science, since the opening of the London Institution. 1842. Printed for private circulation. |