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nitric acid; and therefore, why is an oxide formed which, in the first place enters into combination with the acid, but afterwards remains in the acid an insoluble oxide. The whole of the facts lead me to suppose that Faraday's views respecting the passive state of iron do not give a satisfactory explanation. Bale, October, 1836.
(To be continued in the next number).
The Electric Column considered as a Maintaining Power, or First Mover, for Mechanical Purposes. By George John SINGER, Esq.*
The power of the electric column as a source of mechanical action was first discovered and applied by that excellent philosopher M. De Luc, the admirable inventor of that important instrument; and it is to his active discrimination and unceasing exertions we are indebted for the principal mechanical arrangements which have been employed to render the variable action of the column equal to the production of a constant thouzh unequal motion.
The principal object of such an attempt is to enable an observer to measure the actual variation in the power of the column at different times, and under dissimilar circumstances; and, by a comparison of these changes with the usual meteorological phenomena, to ascertain if any connexion can be traced between the spontaneous electricity of the column, and the natural electricity of the earth and the atmosphere.
For this purpose any arrangement may be employed which is capable either of producing or maintaining the motion of light substances by the immediate action of the column; and that will be most eligible which produces this effect most certainly, and by the least complex means.
With columns of small power, the frequency with which the leaves of Bennet's electrometer are made to open and strike the sides of the glass, during their contact with one extremity of the column, for a certain number of seconds, becomes a measure of the comparative power of the instrument at different times: but its distinct expression is prevented by the tendency of the gold leaves to stick to the sides of the glass; and this arrangement is therefore by no means fitted for permanent observations.
When an insulated conducting substance is freely suspended between two balls, or bells, connected respectively with the opposite ends of the column, I have found that motion is constantly produced if the weight of the pendulum, and the distance of the bells, are exactly proportioned to the acting power of the column at its mean rate of intensity : but if these circumstances are not strictly attended to, the motion will soon cease ; and the want of complete success in the original experiments of M. De Luc and of Mr. B. M. Forster, most probably arose from this cause ; for, in the construction of a
• From Tilloch's “ Philosophical Magazine.”
number of instruments on this plan, I have had but one failure, and in that instance the apparatus was finished in such haste as to preclude a proper attention to the circumstances above stated.
Fig. 1. Plate 3, represents the arrangement of my Electric Chime. A series of about 1600 groups of zinc, silver, and paper discs, are disposed in two columns, separately insulated in a vertical position; the positive end of one is placed lowest, and the negative end of the other, their upper extremities being connected so as to form in effect one series, having at each of its extremities a small bell; between the bells a small ball is suspended by a thread of raw silk, so as to hang at an equal and very small distance from each of them if unelectrified. The action of the column occasions this ball to vibrate between the bells and produce an electric chime, in which the variable action of the instrument at different times is indicated by an increased or diminished velocity of ringing. There is a circular groove in the base of the instrument which receives the rim of a glass shade, by which dust and moisture are prevented from impeding its action.
Fig. 2 represents a convenient modification of the arrangement devised by M. De Luc, and to which he has given the name of Aërial Electroscope. It is constructed nearly in ihe same manner as the chime, but has balls at its lower extreinities instead of bells. From the positive end a wire w, proceeds upwards a few inches parallel to the column, and is then bent into a hook to serve as a support to the pendulum, which consists of a fine silver wire to which a gilt pith-ball is attached. This pendulum, being in conducting communication with the positive extremity of the column, will necessarily recede from it and approach the opposite ball; but it is prevented from actual contact with that ball by a brass fork F, across which a very fine silver wire is stretched. This wire discharges the electricity of the pendulum, and at the same time produces a kind of jerk which prevents the pith-ball from sticking: the pendulum now falls again into contact with the positive ball, but becoming again electrical, recedes from it, and again strikes the cross wire; and in this way, if properly constructed, may continue its vibrations for an unlimited period.
I have sometimes made a variation in this apparatus, by removing the cross wire and the conducting support of the pendulum, and by substituting for it a pith-ball suspended by a silk thread, and accurately proportioned in weight and size to the medium power of the column. By this means the motion occurs over more space than in either of the preceding arrangements, and is therefore more obvious, and well calculated for observation, as the irregularity is considerable, and may be noticed when the temperature of the surrounding medium varies but slightly.
During my employment of the very extensive series of columns I have constructed, I have frequently attempted to produce a rotatory motion by the direct action of their electrical power, but hitherto the attempt has continued unsuccessful ; by indirect means, however,
the same object has of late been very ingeniously obtained. In October last, my friend Mr. Lighifoot, a very active philosopher, who has made many interesting observations on this subject, first suggested the employment of an inflexible pendulum as a means of converting the reciprocating motion usually produced by the columu into a source of rotatory movement; and the correctness of this idea was soon afterwards practically verified by my pupil Mr. F. Ronalds, who with the assistance of a watchmaker, has made a very successful and truly ingenious arrangement, by which a simple and curious electrical clock is produced.
The rotatory motion obtained by this indirect means, is however rather curious than useful; for it is scarcely so correct an indication of the power of the column as the simple pendulum, and requires a much more extensive series to keep it in motion ; it cannot therefore be preferred for the usual purposes of observation, and has I fear very little chance of becoming at all useful as a time-keeper; for the variable action of the column must render it a most irregular maintaining power, which it will be very difficult, if not iinpossible, to correct effectually.
The most elegant and at the same time the most simple movement yet produced by the action of the electric column appears to be that employed by Signior Zamboni, who has made some interesting discoveries on the general structure of the instrument. He employs a vertical needle supported by a delicate pivot or knife-edge a little above its centre of gravity, the position of which may be readily altered by means of a sliding weight attached to the lower extremity of the needle, which may by that means be so adjusted as to possess the properties of an accurate scale-beam, and will maintain its oscillations over a considerable space by a very slight impulse.
The upper end of the needle, for at least an inch, is formed of varnished glass; and on this a ring of gold, or a gilded ball of pith or cork, is fixed; the axis of the needle is supported midway between two vertical columns insulated, but connected together at the bottom, so that the upper ends of the columns become the positive and negative extremities of the series; the upper and insulated extremity of the needle comes in contact alternately with each of these ends, receives its electrical state, and recedes towards the other, where the same process ensues; and thus the vibrations of the needle are maintained with great constancy over a considerable space.
Fig. 3 represents the form I have employed for this construction: the needle is supported by a brass arm which slides on one of the columns; it is suspended by a delicate pivot, and has at its summit a fine varnished glass tube, to which a gilded ball is affixed; the lower extremity of the needle is provided with a sliding weight, by which the relation of the centre of gravity to the point of suspension is accurately adjusted; to render the contacts perfect, and least liable to change, the gilded ball does not strike the brass caps of the columns, but touches alternately two gold wires connected with them.
In this construction the needle is not moved by the direct attraction of the column; but being once put into a state of vibration, its motion, which would naturally decline, and finally terminate by the operation of friction and by the resistance of the air, is renewed at each contact by the impulse of electrical attraction, which is alternately exerted on the needle in opposite directions by each extremity of the column; and as this attraction does not sensibly act on the pendulum until it is very near the attracting surface, its operation commences when it is most wanted, and, without materially affecting the action of the pendulum in any other way, occasions it to describe constantly equal arcs at every vibration.
It is obvious, that by connecting a proper lever and ratchetwheel with the axis of the needle, motion may be readily communicated to indexes, or to other wheels; and this I am informed has been done during the past year, by some experimentalists on the continent. I have since tried the experiment, and find it succeeds perfectly, but requires a more extensive series to overcome the increased friction.
An effect very nearly resembling the action of the beam of a steam engine may be produced by placing the needle in a horizontal instead of a vertical position. For this purpose it should be constructed in the same manner as an ordinary scale-beain; having equal arms terminated by gilt balls, and its point of suspension above its centre of gravity. If a needle of this kind be insulated, and placed with one of its balls a few inches above the positive extremity of a powerful colonn, whilst the opposite ball is similarly situated with respect to the negative extremity, it will, when once put into a state of oscillation, continue to move with considerable regularity, and with a momentum which renders it probable that, by the application of a proper mechanical arrangement, a tolerably regular source of rotatory motion would be obtained.
I have now completed a series of columns comprising upwards of 50,000 groups of a peculiar and powerful arrangement, but have not as yet combined them so as to institute any accurate experiments on their effects; but I trust it will not be long ere I have leisure to accomplish this object.
G. J. SINGER London, May 1, 1815.
GUARDIAN OF EXPERIMENTAL SCIENCE.
ELEMENTARY LECTURES ON ELECTRICITY.
LECTURE XIX. MR. Stephen Grey, a Charter-house pensioner, who discovered the difference between conductors and non-conductors, and other capital facts, appears also to have been the first electrician who entertained the notion of an identity between electricity and lightning. In the concluding paragraph of one of Mr. Grey's papers, printed in the “ Transactions of the Royal Society," the author says, whilst contemplating the results of the experiments he had been describing in the same paper
“ By these experiments we see, that an actual flame of fire, with an explosion, and an ebullition of cold water, may be produced by communicative electricity (communicated to a metallic rod, an iron ball, and other bodies, on which he had been experimenting): and though these effects are at present but in minimus, it is probable that in time there may be found out a method to collect a greater quantity of it, and consequently to increase the force of this electric fire, which, by several of these experiments seems to be of the same nature with that of thunder and lightning.".
These predictions, which were printed in the Transactions for the year 1735, ten years prior to the discovery of the Leyden jar, and about seventeen before the first successful experiments on atmospherical electricity, were wonderfully verified in these two memorable events.
After the wonderful powers of the Leyden jar had become generally known, there can be no wonder of the identity of electricity and lightning being suspected by those electricians who paid so close attention to the phenomena ; indeed, it soon became a prevalent opinion : but it is certainly to Dr. Franklin that the honour is due of earnestly calling the attention of philosophers to this topic Ann. of Elec. Vol. IX, No. 53, Nov., 1842.