magnetic elements

pl. Intensity, declination, and dip. gō, pot, IMG:content-0824.png:[blocks in formation] 2. The branch of science which treats of this property and its conditions or laws. 3. The attractive power itself. The property of magnetism was first discovered in the natural oxide of iron, called Magnetite (q. v.), or the Loadstone. The earth itself having magnetic properties, such a natural magnet pointed nearly north and south, when freely suspended, and also attracted small pieces of iron. It was subsequently discovered that pieces of steel rubbed with natural magnets also became magnets; and these artificial magnets, besides being more convenient, may be much more powerful, so that natural mag nets are now only sought as curiosities. The attraction of a magnet for iron filings is most intense ata short distance from the ends, and decreases toward the middle; at the center there is no attraction, and this center is termed the equator of the magnet. The points at which the magnetism is most intense are termed the poles. It is evident that the magnetism at the two poles is different; and that pole which points to the north is termed the north-seeking pole, while that which points to the south is called the south-seeking pole. If two magnets are taken, and the north-seeking pole of one is brought near the north-seeking pole of the other, they repel each other; but if the north-seeking end of one is brought near the south-seeking end of the other, then they attract each other. Therefore sim ilar poles repel, di imilar poles attract each other. It is impo ible to obtain a magnet with only one pole. If a magnetized needle is broken into a number of small pieces, each little piece is a magnet having a north-seeking and a south-seeking pole. Hence it would appear that every particle of a magnetized body is a little magnet, all having their south-seeking poles set in one direction, and their north-seeking poles in the opposite direction. Bodies may be divided into two cla es: viz., magnetic bodies, which are attracted by magnets, and non-magnetic bodies, which are not attracted. ckhe and cobalt. Some other metals, salts of iron and of magnetic bodies are the metals, iron, nickel, other metals, porcelain pathogens, and ozone, are feebly magnetic. substances, as, for example, bismuth, antimony, copper, silver, gold, lead, sulphur, phosphorus, and water, are not only not attracted by a magnet, but are actually repelled; these are said to be diamagnetic. When a magnetic substance is brought near to or in contact with a magnet, it becomes converted into a magnet by magnetic induction (q.v.), just as a charge is induced in a conductor by an electrified body. The nearest pole thus induced is a di imilar pole to the inducing pole, and the attraction of the magnet is thus due to the action already described of two di imilar poles. When the inducing magnet is removed, most substances lose their magnetism, and hence are said to be temporarily magnetic; the perfection of this property in soft iron is of great importance to magneto-electric and dynamoelectric machines, which depend entirely for their effects upon rapid reversals of magnetic polarity. Steel and nickel retain the greater part of the induced magnetism, and are said to be permanently magnetic. Cast-iron also retains a large proportion of the magnetism imparted to it. Even so-called permanent magnets, however, lose a portion of their power gradually; but by "closing" their poles with pieces of soft iron, which thus become induced magnets with di imilar poles in contact, the inducing effect of these pieces strengthens the magnetism; such pieces of iron are termed armatures. If magnetized steel is heated to redne , or is subjected to violent blows, it loses its magnetism. That a magnetic needle points approximately north and south is due to the fact that the earth itself is a huge magnet, whose conditions accordingly relate to what is called Terrestrial Magnetism. Thus, the North magnetic pole is not at present identical with the true North pole, but is situated within the Arctic circle in latitude 75° 5' N., and long. 96° 46' W. The position of the South magnetic pole has not yet been ascertained. In consequence of the different positions of the magnetic North pole and the geographical North pole, a magnetic needle does not point true north and south, but a little to the east or west, according to the locality. When a needle is balanced on a horizontal axle, so that it can turn in a vertical plane, and is then magnetized, it is found to set itself at an angle depending on the locality, with the north seeking pole pointing downward if north of the equator, and the south-seeking pole pointing downward if south of the equator. This is termed the inclination or dip of the needle, and a needle thus arranged is termed a dipping-needle. Magnetic charts are maps on which are marked lines showing the distribution of the earth's magnet ism. It is found that the three magnetic elements, 2599 as the declination, dip, and intensity of magnetic force are termed, vary not only in different places, but also in the same place, from year to year, from month to month, and even from hour to hour. Those changes which proceed gradually for several years are termed secular. Frequently disturbances occur which produce a temporary irreg ular effect on all the needles over a considerable area; these are termed magnetic storms, and are often connected with manifestation of electrical phenomena, such as the aurora borealis, or a violent thunderstorm, and still more generally with those solar outbursts known as spots on the sun. All such changes in the earth's magnetism are now daily recorded at many stations by self-registering apparatus. Profe or Ersted, of Copenhagen, discovered that if an electric current were pa ed along a wire parallel to a freely-balanced magnetic needle, the needle was deflected to a position at right angles to the current. Subsequently it was discovered that a current pa ed at right angles to an iron wire magnetized the wire so long as the current pa ed. This effect was easily multiplied by coiling the wire conveying the current round the iron rod or wire in the form of a helix, thus producing magnetism enormously more powerful than could be contained in any permanent magnets. Still later it was found that the wire helix alone po e ed nearly all the properties of a magnet. At a subsequent period Faraday discovered the converse relative phenomena, that the production, or ce ation, or any variation in the intensity of magnetism caused the production of an electric current, the developments of which are comprised in the subject of magneto-electricity. Animal magnetism : [ANIMAL-MAGNETISM, MES MERISM.] măg-net-Ist, s. [English magnet; -ist.] One skilled in magnetism; a magnetician.