Abbildungen der Seite

ww, the extremities of which communicate with the mercury in the cell eee. Another connecting wire ff communicates with the mercury in both cells. Cc Cc is a copper vessel made in the form of an Ampère's rotating cylinder, seven inches diameter; in this vessel is placed a cylinder of zinc, as represented by the dotted lines zz. On the outer rim, and at 90° from each other, are soldered four brass studs; to the extremities of which are soldered two brass wire circles (one only of which is shewn in the figure) that cross each other at right angles in the pole P; from which junction descends a pivot that runs in a hole made to receive it in the upper part of the connecting wire ww. The two circles are each 9 inches diameter, and form two great circles of the sphere they are intended to represent. The lower parts of the circles are left open, and the points of the wires bent downwards, till they come in contact with the mercury in · the lower cell. Two other wires proceed from the upper edge of the zinc cylinder, and terminate in the mercury in the upper cell eee, as shewn in the figure.

Things being thus arranged, when dilute acid is poured into the copper vessel, the galvanic action takes place throughout every part of the great circles which represent the sphere; ascending from the copper in the upper hemisphere HH from the equator EE to the pole P; and descending in the lower hemisphere hh from the equator to the mercury in the lower cell, which is the place of the other pole of the sphere. From the poles it is transmitted to the mercury in the upper cell eee, by the conducting wires ww and ff; and both circuits are completed by the wires from the zinc cylinder terminating in this cell. Thus two galvanic circuits are formed by one apparatus ; and hence likewise is solved the apparent anomalous phænomena of galvanized wires or cylinders rotating in different directions on the opposite poles of a magnet.

This delusive appearance is completely relative, and similar to our notions of up and down ; but with respect to the magnet, and in reality, the rotation is the same on both poles : for example, let any person turn first towards the north, and then towards the south ; by observing the heavenly bodies, they would appear to revolve to the left in the former, and to the right in the latter case; yet the rotative motion of the earth (which is the cause of their apparent motion) is constantly the same way. In this experiment both poles of the magnet are acted on at the same time by similar galvanized wires, and the machine rotates by the joint influence of the former on the excited wires of the latter. Owing, however, to the weight and size of the machine, the rotation is but slow at the beginning of the experiment, but soon acquires considerable velocity, and the generating force, added to the acquired momentum, keeps it in motion for a length of time.

Well aware of the difficulties that would arise at the present day in any endeavour to support an hypothesis of the earth's being hollow, and containing within it a spherical magnet, as was the opinion of Dr. Halley, I have confined myself to a detail of the experi


ment only, without obtruding either remark or opinion. The success of this experiment, however, so satisfactorily confirmed my expectations, that the principle upon which it was made could hardly fail to intimate its applicability to others of a like nature ; one of which being intimately connected with that I have just described, this may, perhaps, be considered no improper place for its detail.

The experiment for rotating the magnet on its axis, it is well known, was first made by M. Ampère ; but the manner in which as yet it has been exhibited, like all the other similar experiments, shews the action only on one-half of the magnet at one time ;-and by reversing the poles (everything else remaining as before) it appears to rotate in a contrary direction.

I hope, however, that I have satisfactorily proved that this apparent contrariety of rotation is merely relative, and that the real motion is the same in both cases. If possible, however, the experiment I am about to describe will confirm this property in a still more satisfactory manner.



The rotation of the magnet on its axis by subjecting both poles at the

same time to the influence of similar electric currents. Fig. 3 is an elevation of the appa

3. ratus; and, with the exception of the magnet NS, is entirely of brass-work. A is a round foot, from which rise the two cheeks BB, for the purpose of supporting

AN the annular cell qq holding quicksilver;

BI and likewise the cross piece R, which

B is screwed tight down by the knobs k k, and thus the apparatus is kept firm and

z steady. The magnet passes through the opening in the centre of the cell 99, and

g communicates with the mercury there contained by means of a wire soldered to its equator, and at right angles to its axis. C The poles are furnished with pivots; the lower of which at S runs in a small cup on the top of the foot A; and the upper one at N runs in the lower extremity of a screw nail passing through the cross piece R, and whose head is made into the form of a cup for holding mercury. ZC are two wires proceeding respectively from the zinc and copper side of a battery: the former communicating with the mercury in the cell 99, and consequently with the equator of the magnet ; the latter communicates with the upper pole N in the manner shewn in the figure. Thus, one-half of the magnet forms part of the galvanic circuit. The other half, from its equator to the lower pole S, forms likewise part of another similar galvanic circuit, by means of the wires Z' C' which proceed respec

tively from the zinc and copper sides of another battery, and communicate with the equator and pole in the same manner as the former. By subjecting the magnet in this manner to the influence of like electric currents, it is rotated with an astonishing velocity, but which may in a moment be retarded by interrupting the circuit of either battery; and again accelerated by renewing the contact. This variation of the experiment proves to demonstration the utility of employing both poles at the same time, and is another proof of the rotations on opposite poles, in the old experiments, being merely relative ; for the poles of the magnet are here both connected with the copper side, and the equator with the zinc side of the respective batteries. Another advantage in the manner of making this experiment is, that the glass vessel and mercury for floating the magnet are here not used; therefore the whole of the magnet is in view ; whereas in the old mode, only a small portion of the magnet, about the thickness of a quill, was visible above the surface of the mercury. It can be no small gratification to those who are in the habit of giving public lectures, to be enabled to exhibit this experiment to the satisfaction of a large audience; for as the lecturer can now have his rotating magnet of almost any size he pleases, and likewise of any figure, this interesting experiment may be viewed from the remotest part of the lecture-room. Another inconvenience I have almost entirely removed both in making this and every other electro-magnetic experiment. My batteries are of such a peculiar construction as not to annoy the experimenter by the escape of hydrogen ; neither is the expense of making the experiments more than one-fortieth of any other method yet made public; yet the apparatus in general is of large dimensions; for instance, the sphere in the former experiment is 9] inches diameter; and the magnet in the latter is 8 inches long.

I should now proceed to the description of other new experiments, were I not confident that I have already intruded upon your valuable pages. That task must therefore be deferred for the present. Some of the minor of those experiments are,—The rotation of the cylinder by the influence of an external magnet;-Ampère's cylinders rotated independent of each other's weight;—Thermo-rotation on both poles of the magnet ;-Electro-magnetic bells, &c.

In summing up the results of the two detailed experiments, it appears from the first,

That similiar electrized wires rotate in the same direction round both poles of the magnet;

That both the copper and zinc cylinders are here carried round the magnet in the same direction ;

That a sphere, conducting similar currents of electricity from its equator to its poles, will rotate by the influence of an internal magnet.

And from the second it is evident that, had the magnet in the first experiment been free to move, it would likewise have rotated

The ro

at the same time with the sphere containing it. This property would seem somewhat conformable to the opinion of Halley, who supposed the earth to contain a spherical magnet, which rotated within the shell that we inhabit. And, what is more fortunate to the analogy, it is proved by the experiments that when the electric currents are of the same kind from the equator to the poles of both nucleus and shell, they both rotate in the same direction. tation would likewise be as effectual, were the magnetic poles removed to some distance from the axis of motion.

Another hypothesis might be advanced to account for the rotatory motion of the earth, and which would not require the supposition of its being hollow; but only to be regarded as a grand natural magnet, possessing a capacity for conducting the electric fluid. The former of those properties is admitted by almost every writer on magnetics; and the latter, it is presumed, will be as readily conceded.

From the second experiment we see the magnet rotate on its axis by the influence of electric currents from its equator to its poles. Had the magnet been a sphere instead of a bar, it might have represented the earth or planet more perfectly; but its figure, it is presumed, can make no difference in the result of the experiment.

It is now well known that electricity can be excited by heat, and the success of thermo rotations in the manner that I obtain them would, if formed into a sphere, depend upon the difference of temperature between the equator and poles. This property is obviously analogous to the natural state of the earth; for the sun exerting his greatest influence a few degrees only on each side of the equator, the polar regions are constantly kept at a very low temperature; so much 80, that every attempt yet made to explore them has been rendered abortive in consequence of a prevailing intensity of cold; whilst the equatorial parts, it is well known, are as constantly kept in the other extreme, That thunder and lightning are by far more prevalent in the torrid than in ihe friged zones, is a fact that cannot be denied ; and that this difference of electrical phænomena is principally caused by the superior action of the sun in those parts, appears more than probable. Hence it may be fairly concluded, that the action of the sun either partly or wholly governs the general electrical phænomena of nature; and, either by producing or exciting this wonderful agency in the equatorial regions, dispenses its influence from thence to the poles of the earth.

Another circumstance that would be something in favour of the hypothesis is, that a magnetic body free to move in any direction, (a sphere suspended in space, for instance,) and having currents of electricity passing over its surface to its poles, would not only rotate, but would likewise maintain its parallelism. This may be easily demonstrated upon the principles shewn in Professor Barlow's



"Magnetic Attractions," second edition, p. 249, under the head Electro-magnetism. Let NZC'Z', fig. 4, represent the

4. magnetic sphere. NS its poles. Likewise suppose ZC and Z'C, to proceed

N from the zinc and copper sides of two batteries of equal power. Then the electric force in that part of the magnet between Z and C, or in the northern Z hemisphere, will tend to carry the pole N towards n. And the electric force in the southern hemisphere between Z' and C will at the same time have a like tendency to carry the same pole N towards n'. But the pole N being acted on by the two equal and contrary forces, can have no tendency to either of these points ; therefore must of necessity remain in its original position.

That pole of the magnet which possesses the same kind of magnetism as the north magnetic pole of our globe, being now properly called north ; when the zinc sides of the batteries are applied at the equator, the magnet rotates from west to east , or, in the same direction as the earth.

Having pointed out these particulars, most of which are facts deducible from experiment, there can appear no extreme improbability that most of the phænomena which are observed to obtain with the heavenly bodies in our system, are physically produced by the powerful agency of electricity. And experiments may, in my humble opinion, be instituted, that would satisfactorily exhibit the whole ; for we have already seen that rotation and parallelism are producible by electro-magnetism ; and the thermo experiments serve to prove that the influence of the sun may be sufficient to excite continual electricity. Hence magnetic bodies placed within its influence may not only rotate and keep their axes parallel, but probably may likewise obey every other observed astronomical law with regular mathematical precision.

I am, gentlemen,

Your most obedient servant, Artillery Place, Woolwich, Aug., 1824.

WM. STURGEON. (To be continued.)

NOTICES OF NEW BOOKS, &c. The Eighth Annual Report of the Royal Cornwall Polytechnic

Society. SIMPKIN and MARSHALL, London. The volume before us is another indication of the advancing usefulness of this highly valuable Society, and of the great importance to the advancement of the arts, manufactures, &c. of this country,

« ZurückWeiter »