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If two needles be suspended from any given pole of a magnet, they will diverge, because they both require the same polar arrangement. If a bar of iron be laid on that pole of the magnet, the divergence will diminish, because the next end of the iron will require the disposition of the opposite pole, and consequently, counteract the repulsive power of the magnet.
A magnet will not transmit its power through a bar of iron, if this be too long. Muschenbrouck limits their length to six feet, but this depends on the strength of the magnet.
The power of a magnet (every thing else being equal) depends on the numbers of its surfaces magnetically arranged, and the accuracy of that arrangement.
The arrangement is accurate when the synonimous surfaces are exactly parallel to each other, and originally conformed to and parallel with those of the great general magnet.
The magnetic attraction is strongest in the direction perpendicular to the magnetic surfaces, and weakens in proportion to the magnitude of the angle of direction with the perpendicular, and consequently, is null when at a right angle with it. Hence the magnetic power seems concentrated at the poles, and the lateral powers are the weakest, as they originate only in the oblique direction of surfaces, or from surfaces inaccurately arranged.
If the south pole of a magnet be charged with filings of iron, and then approached to a bar of iron standing erect, part of the filings will drop off, because the poles of the same name, by exciting a contrary arrangement, weaken each other ; but if the filings were suspended from the north pole of the magnet, it would take up still more of the filings, as the opposite poles strengthen each other; the uppermost pole of the iron in this case, becoming magnetic by position.
If the synonimous poles of two magnets of equal powers be approached to each other, if the powers be very unequal, the stronger immediately destroys the weaker, and inducing a contrary disposition attracts instead of repelling it; if the powers be less unequal, it requires a longer time ; so also, if one be softer than the other. Even if their powers be equal, yet, after some time, the softer will yield to the harder. If both be equally hard, they only weaken each other.
If a magnet be cut in two, in a direction parallel to the axis, the parts before conjoined will now repel each other, because they still retain two synonimous poles.
But if the magnet be cut in two in a direction perpendicular to the axis, the two ends before conjoined will now attract each other.
If a magnetic wire be twisted, its powers are so disordered that one side of the wire, in some places of it, will be attracted and the other side repelled by the same pole of the magnet.
The power of the magnets (cæteris parib.) is in proportion to their surfaces, or as the squares of their diameters.—See Hutton's Magnetism, p. 72.
Communication. When iron is applied to or brought within the sphere of activity of a particular magnet, it acquires the arrangement requisite to form the heteronymous pole, and thus becomes itself in some degree magnetic in its whole length, if this length be not totally disproportioned to the power of the particular magnet.
Hence the other end of such bar of iron acquires the arrangement of the opposite pole, according to the laws of crystallization already laid down.
Iron becomes magnetic either by contact or proximity to a magnet, or by position, or by internal commotion.
If a bar of iron be placed in a vertical position, its insensible fibrillæ gradually acquire the magnetic arrangement, so that after some years it becomes a complete magnet, its lowest part becoming a north pole, that is, pointing, when free, to the north, and the upper a south pole. In the south hemisphere the under end becomes a south pole.
A bar of iron not previously magnetic, does not acquire this disposition in the slightest degree while lying in a horizontal or nearly horizontal disposition, but if one end of it be raised, it immediately acquires it in some degree, as appears by approaching a magnetic needle to either end, because in that direction it is then exposed to activity of the polar ends of the great general magnet.
But if a bar of iron be heated, though only at one end, and while hot set in a vertical or nearly a vertical position, it will acquire the magnetic power much more readily.
So also if one end of a bar of iron not magnetic be struck against the ground, it will become in some degree magnetic, the lower end becoming a north pole, &c. ; and if afterwards the other end be struck in the same manner, the poles will be reversed.
Hence it is evident that any motion communicated to the integrant particles of iron, placed in a proper situation, helps them to assume the magnetic disposition already impressed upon them by the great general magnet.
If the opposite poles of two magnets of equal power be approached to each other, the power of both is increased ; and if one of them be more powerful than the other, it will increase the magnetic disposition, and consequently the power of the weaker.
Soft iron, as its parts are most easily moved, receives the magnetic disposition most easily ; hard iron or tempered steel more difficultly, and cast iron, as being both hard and abounding in the heterogeneous particles, most difficultly and imperfectly.
Whatever way iron is applied to a magnet the magnetic power is diffused in the direction of its length. Hence it should seem that when a bar of iron is laid on a magnet, the contiguous ends of the iron become poles of the same name with those of the magnet to which they are contiguous, and hence may be derived the power of
armed magnets, for the surfaces of the armour immediately beneath those of the magnet impress a direction opposite to their own on those of the magnet, and consequently rectify such surfaces of the magnet as may have been inaccurately directed, and thus strengthen it.
To communicate the magnetic power to iron by friction against a magnet, it is necessary that its pole should slide along the magnet several times in the same direction, for if the directions be alternately opposed, the powers received will successively destroy each other.
A synonimous pole is formed at the end at which the friction begins to that of the magnet applied, and an opposite at that at which it terminates,
Appropriation to Iron. It has of old been observed that the magnetic phenomena were peculiar to iron, and the reasons why they are so have been already assigned, but of late some semi-metals have been observed to partake of these properties, as nickel, cobalt and manganese ; this has been thought to arise from a mixture of ferruginous particles, from which they can be scarcely freed, and with respect to manganese, and in many cases of the others also, this seems to hold true; but with respect to nickel, and in some instances of the others also, the magnetic properties they discover seem to me to proceed from their great attraction to iron, particularly when their particles are duly arranged, for then they are exposed to the power of the great general magnet, which acts on them in proportion to this arrangement and their affinity to iron.
Of Inclination and Declination. These phenomena, which are so different in different parts of the globe, and even in different seasons and hours of the day, not being as yet noted with sufficient certainty and precision, I shall, for the present, decline entering into their explanation.
On the Electricity produced by Evaporation.
(Continued from page 186.) In the first paragraph of page 186, we have stated that “the curiositity of philosophers concerning Volta's experiments having become subsided, we hear little more of the production of electricity by evaporation till the celebrated experiments of Messrs. Armstrong and Pattison." Since the publication of that historical sketch, we have been reminded of the following series of experiments, on this subject, by the Rev. Abraham Bennet, prior to the year 1782.
"In a treatise on electricity by M. L'Abbe Hauy,” says Mr. Bennet, “I find that since M. Volta's discovery of electricity produced by
evaporation of water from hot coals, Messrs. Lavoisier and De la Place have remarked, that bodies passing from a solid or fluid state into vapour, give unequivocal signs of positive or negative electricity. A large vessel containing a quantity of iron filings was insulated and connected with M. Volta's condenser. Three parts of water and one of vitriolic acid were poured upon the filings, which caused a brisk effervescence, and a rapid discharge of inflammable air, and in a few minutes the condenser became so strongly charged that it gave a very sensible spark, and by the electrometer it was found to be negative. The production of fixed and nitrous airs had the same effect; also chafing dishes insulated and filled with lighted coal produced very clear signs of negative electricity after the combustion of the coal. It appears that in these experiments, the substances evaporated carry away from the vessels with which they are in contact a part
their natural electricity ; but when water was poured upon red-hot iron pans, the electricity was no more negative, as in the former experiments, but decidedly positive. These experiments were communicated to the Academy of Sciences in the year 1781.
M. de Saussure has also tried many experiments of this kind by plunging hot iron and other metals in water, and pouring water into crucibles of iron, brass, copper, silver, or porcelain. Sometimes he used distilled water, also spirits of wine and ether, and in these experiments the electricity was sometimes positive, sometimes negative, and sometimes neither.
M. de Saussure thinks that when the operation which converts the water into vapour at the same time decomposes it, or the body with which it is in contact, it produces a new quantity of the electrical matter, and that the vessel used in the operation becomes positive, negative, or neither, according as the fluid produced is superior, inferior, or equal to that which is taken from the vessel by evaporation. An account of these curious experiments is contained in the second volume of M. de Saussure's Travels over the Alps, page 227.
The gold leaf electrometer being we'l adapted to the performance of experiments of this kind, I was induced to repeat some of them with variations, in hopes of new appearances : and since almost every substance in the whole chemical nomenclature may thus be subjected to the action of fire, and its affinity with electricity in a state of vapour examined, new facts may yet arise which will produce new theories; therefore, the following experiments are placed in the order they were tried, without regard to system.
Experiment 1.—A bason of tinned iron about six inches wide at the bottom, and eight inches at the top, was placed upon the
of a gold leaf electrometer. The bottom of the bason was covered with water about an inch deep. An iron chissel was heated red-hot, and dropped into the water, one end being immersed and the other resting on the edge of the vessel. The gold leaf gradually opened about an inch negatively, then closed and opened positively, remaining positive to the end of the experiment.
2.-The chissel was heated more than in the last experiment, and the gold leaf struck the sides of the electrometer six times negatively; then it changed, and stood at half an inch positive to the end.
3.—The chissel was again made very hot, and it caused the gold leaf to strike often negatively; after which it closed, but never opened positively.
4.--The chissel was heated very much by blowing the fire, and it caused the gold leaf to strike fourteen times negatively, but no positive electricity appeared. This was repeated about twenty times without any production of positive electricity.
5.–Upon observing that the chissel was much calcined upon its surface, by being so frequently heated in the above experiment, I rubbed off the calx and heated it again, and found that now it produced first negative and then positive electricity, as before ; whence it appeared that its production of positive electricity depended upon the metallic state of the iron.
6.-A large bar of copper and a piece of brass were heated redhot and plunged in the water, which also produced first negative and then positive electricity.
7.—Melted lead was dropped into water contained in the bason as above, which gradually opened the gold leaf positively.
8.-Melted lead being dropped into a deep narrow vessel almost full of water, did not electrify it, since it emitted no vapour. It is, therefore, not the mere decomposition of the metal, but the formation of a certain kind of vapour, which excites electricity.
9.--Boiling mercury was dropped from an earthen crucible into a small quantity of water in a porcelain cup standing upon the cap of the electrometer, which caused the gold leaf to open positively.
10.-Several thin pieces of bell metal were heated red-hot and dropped into the water, which caused a negative repulsion only.
11.-An earthen unglazed flower pot was half filled with red-hot cinders ; then the other half was filled with chopped grass, which caused the gold leaf to open with positive electricity, and to continue striking the sides a considerable time. In the same manner were tried cabbage leaves, lettuces, turnip tops and roots, and chick weed, with the same results.
12.-Turnings of dry ash wood were thrown upon the hot cinders as above, which smoked much without causing any repulsion of the gold leaf till water was added, which caused a strong positive elec-tricity.
13.-Dry hay was burnt in the flower pot, as above, which produced no electricity till water was added, and then it became strongly positive.
14.—The flower pot was placed upon the electrometer with redhot cinders alone, and water was dropped into the middle, which opened the gold leaf negatively; then, dropped near the side, opened it positively; again in the middle, negatively. 15.-Since the cinders became more positive and negative with