netic researches, M. Oersted has obtained several additional results of a very interesting nature. He found that the electro-magnetic effects do not depend upon the intensity of the electricity, but solely on its quantity. A plate of zinc of six inches square, immersed into a vessel of copper containing the dilute acid, produces a considerable electro-magnetic effect; but when the plate has 100 square inches of surface, it acts upon the needle with such force, that the effect upon it is sensible at the distance of three feet. The effect is diminished rather than increased, when forty troughs, similar to this single one, are united in one battery. M. Oersted found, that the discharge of a strong electric battery, transmitted through a metallic wire, produced no deviation in the needle; neither did a series of uninterrupted sparks produce any other effect than the ordinary attractions and repulsions. A galvanic pile of 100 discs of two inches square each, and paper moistened with salt-water, is also destitute of any sensible effect.

In comparing the effect of a single galvanic arc with that of an apparatus composed of several, M. Oersted supposes the annexed figure to represent a galvanic arc

composed of one piece of zinc z, a piece of copper c, ametallic wire ab, and a fluid conductor l. The

zinc always communicates a portion of its positive electricity, to the water, as the copper does of its negative electricity, which would produce an accumulation of negative electricity in the upper part of the zinc, and of po

sitive electricity in the upper part of the copper, and the communication by ab did not re-establish the equilibrium by presenting a free passage to the negative electricity from z to c, and of the positive electricity from c to z. The wire ab, therefore, receives the negative electricity of the zinc, and the positive electricity of the copper; whereas a wire which forms a communication between the two poles of a battery, receives positive electricity from the pole of the zinc, and negative from that of the copper.

"If we attend to this distinction," says M. Oersted, "we may, with a single galvanic arc, arranged as I have described, repeat all the experiments which I had before made with a compound galvanic apparatus. One great advantage of this plan is, that we may form the arc sufficiently light to be suspended by a small metallic wire, so as to revolve round the axis of the wire prolonged; and in this way we may examine the action of a magnet on the galvanic arc.

"For this purpose I employed the arrangement, annexed, which is a perpendicular section of it in

the direction of its breadth, cccc being a trough of copper 3 inches high, 4 inches long, and inch wide; zz, a plate of zinc, kept in

of a line diameter; ab, a brass wire as small as possible, but capable of sustaining the apparatus; and cac, a linen thread for attaching the wire to the apparatus. The trough contains the usual conducting fluid. The uniting wire of this apparatus will attract the north pole of the needle when it is placed on the left side of the plane cffffz, regarded in the direction fz. On the same side, the South pole will be repelled. On the other side of this plane, the north will be repelled and the south pole attracted. In effecting this, we must not place the needle above ff, nor below fz or fc. If, instead of presenting a small moveable needle to the uniting wire, we present it to one of the extremities ff, one of the poles of a strong magnet, the attraction or repulsion (indicated by the needle) will cause the galvanic apparatus to revolve round the prolonged axis of the wire ab.

If we substitute, in place of the conducting wire, a large ribbon of copper of the same breadth as the plate of zinc, a feebler effect only is produced. The effect is on the other hand increased by making the conductor very short.

This figure represents the perpendicular section of this arrangement in the direction of the breadth of the trough; and the annexed is a perspective view of it, in which abcdef represent the conduct ing plate, and ezzf the plate of zinc. Here the north pole of the needle will be attracted towards the plane of abc, and the

contrary effects. In this apparatus the extremities act like the poles of the needle, but it is only the faces of the extremities, and not the intermediate parts

that have this analogy.

A moveable galvanic apparatus may also be made of two plates, one of copper and one of zinc, twisted into spirals, and suspended in the conducting fluid. This apparatus is more moveable, but greater precautions are necessary. to avoid deceptions when experiments are made with it.

I have not yet discovered a method of making a galvanic apparatus direct itself towards the poles of the earth. For such a purpose the apparatus would require to be much more moveable.

In repeating the interesting experiments of M. Oersted, sir Humphry Davy found, that the uniting wire of platina was magnetic from its power of attracting iron filings. This wire was also found to communicate permanent magnetism to steel bars transversely attached to it, or placed transversely at some distance from it; while the same bars, when placed parallel to the wire, had only a temporary magnetism when in the vicinity of the apparatus.

The most important fact, however, in sir Humphry Davy's experiments, is, that when the electricity from a Leyden battery is passed through a wire or through air, the wire and air and the sur

rounding space became magnetic, so that bars of steel made tangents or sines or circles round the wire, all became magnets, the north pole of one being opposite to the south pole of the other. By means of a powerful Leyden battery, sir Humphry has made magnets at the distance of fourteen inches from the wire. He has also been able to attract and repel bars placed in the voltaic circuit by the common magnet.

Mr. Ampere communicated to the Academy of Sciences three memoirs, on the 18th and 25th of September, and the 30th of October, 1820. The following are the principal conclusions deduced from the second memoir :

1. "The two electric currents attract one another when they move parallel and in the same direction, and they repel one another when they move parallel and in opposite directions.

2. It follows, therefore, that when the metallic wires through which these currents are transmitted, can only turn in parallel planks, each of the two currents tends to bring the other into a situation where it may be parallel to it, and in the same direction.

3. These attractions and repulsions are absolutely different from the attractions and repulsions of ordinary electricity.

4. All the phenomena discovered by M. Oersted, and which I analyzed, and reduced to two general facts in my first memoir, are embraced by the law of the two electrical currents (§ 1.), admitting that a magnet is only an assemblage of electrical currents, produced by the mutual action of the particles of steel, analogous to that of the elements

of a voltaic pile, and which move in planes perpendicular to the line which joins the two poles of the magnet.

5. When the magnet is in the situation which it tends to take by the action of the terrestrial magnet, these currents have a direction opposite to that of the apparent motion of the sun, and hence when we place a magnet in a contrary position, so that the poles which point to the poles of the earth are of the same name, the currents will be found in the direction of the apparent motion of the sun.

6. This law embraces the phenomena of the ordinary action of magnets.

7. It embraces also the phenomena of terrestrial magnetism, by supposing electrical currents in planes perpendicular to the direction of the dipping-needle, and which move from east to west.

8. There is no difference between the poles of a magnet, than that one of them is found to the left, and the other to the right of the electric currents, which give to steel the magnetic property.

9. When Volta had proved that the positive and negative electricities of the pile attracted and repelled one another, according to the laws of ordinary electricity, he did not demonstrate completely the identity of the two fluids put in action by the pile and by friction; but it became a physical truth, perhaps, when he showed that two bodies, one of which was electrified by metallic contact, and the other by friction acted upon one another in every case, as if they had been both electrified by the pile, or with

the ordinary electrical machine,the same kinds of proof are obtained with respect to the identity of the attractions and repulsions of electric currents and magnets. Magnetic attractions and repulsions, therefore, ought not to be assimilated to those which result from electrical tension, but to those which I have observed between two currents.

M. Ampere has communicated in his third Memoir, several very important results. He has succeeded in directing the uniting wire (fil conjonctif) by the action of the earth. Setting out from his method of considering the phenomena presented by the uniting wires of magnets, he concludes, that the moveable part of the uniting wire ought to form a curved plane, and almost shut, so that there remains only between its extremities an interval necessary to enable it to communicate with the pile, and that then the plane of this curve will be carried by the action of the terrestial globe in a direction perpendicular to that of the dipping-needle. This conclusion has been fully confirmed by experiment.

According to the manner in which he suspends this part of the uniting wire, he has obtained the motion in a horizontal direction, which corresponds with the declination of the compass, and a motion in the magnetic meridian corresponding to the dip.

On the 30th October, 1820, M. Biot presented a memoir to the academy, on the Physical Laws of the Electro-Magnetic Phenomena, which he had deduced from measures of the deviation and the oscillation experienced by needles placed near the uniting wire.

The following is the general expression which he has given of the action exerted at a distance upon a particle of austral or boreal magnetism, by a very fine uniting wire of copper, of an indefinite length, and put in communication with the two poles of a voltaic apparatus.

From the point where the particle resides, draw a perpendicular line to the axis of the wire. The force which acts upon the particle is perpendicular to this line and to the axis of the wire. Its intensity is in the inverse ratio of the simple distance. The nature of its action is the same as that of a magnetic-needle, which is placed tangentially to the contour of the wire, so that a particle of austral and a particle of boreal magnetism would be drawn in opposite directions, though always in the same straight line determined by the preceding construction.

On the Action of the Mineral Acids on the Chlorurets of Gold.To have an exact idea of this subject, we must revert to the facts already generally known. In evaporating the solution of gold in nitro-muriatic acid, the compound, which has at first a gold colour, becomes of a deep red as soon as all the water is evaporated, and if now cooled, it congeals into a very deep redbrown mass, very fusible and so. luble again in water, returning to its yellow-red colour. But if instead of cooling the salt it is farther exposed to heat with precaution, chlorine is given out, and the residue becomes of a lemon-yellow, insoluble in water, but liable to be decomposed by it in a certain time, and then partly soluble in this fluid. The

red-brown mass is a true chloruret of gold the lemon-yellow residue is a sub-chloruret. If the latter is still farther heated, the whole of the chlorine escapes, and the gold alone remains. From these data one may easily conceive the action of the mineral acids on the chloruret of gold. If to its solution (containing no excess of muriatic acid), concentrated sulphuric acid is added in small quantity, no change takes place; if much is added, a red precipitate appears, which turns yellow, and re-dissolves on adding water. This precipitate is an hydrous chloruret of gold. If after having added sulphuric acid to the above solution the liquid is heated and evaporated, as soon as the acid is sufficiently concentrated to bring the temperature to about 2900 Fahr. an abundance of chlorine escapes (not muriatic acid), and a yellow sub-chloruret of gold falls down; generally, however, mixed with metallic gold, the result of the long continued action of the sulphuric acid. It appears, therefore, that the action of this acid upon the chloruret of gold is merely that of a medium for the transmission of heat. The phosphoric and arsenic acids, and generally all the mineral acids that are saturated with oxygen, and can be raised to a high temperature, have the same action as the sulphuric on the chloruret of gold. The nitric, and other acids saturated with oxygen, but volatile by heat, have no remarkable action on the chloruret of gold. When the acids saturated with oxygen are put in contact with the sub-chloruret of gold, another order of phenomena takes place, but apparently depending only on the water which these acids con

tain. The effect of water alone on the sub-chloruret is this: the metallic salt is decomposed, one portion of the gold which it contains (a third, according to Berzelius) is precipitated in abandoning its chlorine to the other portion, which now becomes soluble chloruret, and dissolves in the water. When, therefore, the sub-chloruret is put in contact with a mineral acid saturated with oxygen, if the acid is freed from water, as the vitreous phosphoric or boracic acids, no action is observed between the metallic salt and the acid; but if water is present, the salt changes to soluble chloruret, and metallic gold is precipitated. This takes place sooner, in proportion as the acid is more aqueous, and it is even speedier in a moist than a dry atmosphere, and is assisted by moderate heat. But in no case is there disengagement of chlorine or formation of free muriatic acid, unless evaporation be pushed to the extent described in a former paragraph, on the effects of sulphuric acid assisted by strong heat.-Ann. de Chimie.

On the Action of Salts on the Chloruret of Gold.-If the acids could unite to oxyd of gold, and form true saline compounds with it, the most favourable circumstances to produce these compounds would certainly be found in the play of double affinities. However, salts of gold have never been formed by this method, but only mixtures, when solutions of phosphate of soda, &c. have been added to the chloruret of gold. Some peculiar appearances have occurred on using the sulphate and nitrate of silver. When a solution of sulphate of silver is added to liquid chloruret of gold,