Magnetism

(mag'nět-izm.) (Phys.) That science which investigates the phenomena exhibited by natural and artificial magnets, and the laws by which they are governed. Some of the properties of the magnet were known to the ancients, but they were not acquainted with its directive power, that is, its tendency to a ume a certain position when at liberty to do so. If a light bar of steel be suspended horizontally by a silk thread, or balanced on a pivot, and then magnetized, it will, except at the magnetic equator, lose its horizontal position, making an angle with the horizon, called the angle of dip, and will no longer rest in every position, but will a ume one in a direction north and south, but making a small angle with the plane of the terrestrial meridian, termed the angle of variation. These two angles are subject to perpetual but slight changes. The magnetic equator seems to cro the terrestrial at four points. The lines at which the angles of dip are equal are called magnetic parallels. There are probably no precise points which can be called magnetic poles. The earth being a great magnet, its poles are rather regions than points. Even in the ordinary artificial magnet, the poles are diffused over comparatively large spaces. The earth is most probably an electro-magnet, magnetized by the electric currents continually circulating round it, and which are due to evaporation, . The lines formed by points on the earth's surface, at which the variation is equal, are called lines of equal variation. The rapidity with which a needle vibrates, if drawn from its natural position, is a measure of the intensity of M. at that time and place, and this intensity is subject to constant change. A magnet, if placed in iron filings, will attract them in quantities large at its poles, and diminishing towards the centre, to which none adhere. The poles of a magnet will attract pieces of soft iron; and these, as long as they are in contact with the magnet, will themselves be magnetic, and will attract other pieces of iron or iron filings. If soft iron be brought near a magnet, it will be magnetized, and, as long as it is near it, will attract iron filings, . The interposition of paper, gla , & c., will not cause the magnetic influence to be intercepted. If a magnetized bar of steel be placed under a sheet of paper, iron filings scattered over the paper will arrange themselves in curves over the poles. When soft iron is removed from the magnet, it instantly ceases to be magnetic. Steel is not so powerfully magnetized, but, on removal, it retains more or le of the M. Iron rods or bars acquire polarity by standing long in one position. Magnetism is destroyed by a red heat. If discs of various metals are put in rapid rotation, they will become magnetic, since they will deflect the needle - an effect not due to vorticity produced in the air, since it is more powerful in vacuo. Magnetic attraction and repulsion vary inversely as the squares of the distance. Mag'netism.(Animal,) is, according to those who believe in it, the influence that a man can exercise on the body of another man, either by the application of hands upon him, or the will only. The produced effects are, according to cases and persons, a light and penetrating warm somnolency, more or le deep sleep, external insensibility-partial or total somnambulism with or without lucidity; sometimes spasms, catalepsy, ecstasy. Often, also, no effects are produced. The origin of the term was a fancied analogy between the action of the mineral magnet and that of the animal energy, vis vitæ, but magnetizers admit now that the magnetic fluid is identical with the nervous fluid, and that, since the will directs the nervous fluid to the organs to put them in motion, it can also cast out this fluid and make it to penetrate the body of another person. They think that by accumulating this fluid into the body of a person 3W who is deficient with it, it is po ible to restore equilibrium in it, and to increase vital force. They a ert also that M. may cure, or at least relieve, many diseases, chiefly those which belong to the nervous system. A. M. originated thus:-A German physician, named Mesmer, in 1772 attempted cures with the mineral magnet, and excited some sensation in Vienna; when at length he declared that the effect was produced, not by the magnet, but by a mysterious power in his own person, and that this power was related, not only to the magnetic power, but to the attraction disposed throughout the universe. From Vienna he went to Paris, where he gained many proselytes to his pretended discovery. The government at length appointed a committee, among whom was Dr. Franklin, to investigate the pretensions of Mesmer, and the result of their inquiries appeared in a memoir,by M. Bailly, which condemned animal magnetism. After the lapse of half a century, it has again revived, and numbers of eminent persons are found among its votaries. Though Mesiner is considered to be its discoverer, it was undoubtedly practised by many persons, and in various forms, long before him. [s. 569]