Magnet

(mag'nět.) [From Magnesia, a city of Lydia, where the attracting property of loadstone was first noted.] (Phys.) A body which has the property of attracting iron and certain other metals in a particular manner. There are permanent magnets (see LOADSTONE), and temporary magnets (see ELECTRO-MAGNET). When a bar or needle of steel is rubbed with a M., it acquires magnetic properties. Such bars are called artificial magnets. They are more powerful than natural magnets. When a small particle of soft iron is suspended by a thread, and a magnet is approached to it, the iron is attracted towards the M., and some force is required for its removal. The force of the attraction varies in different parts of the M. It is strongest at the two ends, and is totally wanting in the middle. This variation may also be seen very clear A ly when a magnetic bar is placed in iron filings. These become arranged round the ends of the bar in feathery tufts, which decrease towards the middle of the bar, where there are none. That part of the surface of the bar where there Fig. 458. MAGNETIC NEEDLE. is no visible magnetic force is called the neutral line; and the points near the ends of the bars where the attraction is greatest are called the poles. Every M., whether natural or artificial, has two poles and a neutral line. The end pointing towards the north is called the north pole, and the other end is the south pole. The two poles of a M. appear identical when they are brought in contact with iron filings, but this identity is only apparent. For when a small magnetic needle, ab (Fig. 458), is suspended by a fine thread, and the north pole, A, of an other needle is brought near its north pole, a, a repulsion takes place. If, on the contrary, A is brought near the south pole, b, of the movable needle, the latter is strongly attracted. Hence these two poles, a and b, are not identical, for one is repelled and the other attracted by the same pole of the magnet, A. It may be shown in the same manner that the two poles of the latter are also different, by succe ively presenting them to the same pole, a, of the movable needle. In one case there is repulsion, in the other attraction. [s. 568] IMG:p0613_0.jpg:Gravür IMG:p0613_1.jpg:Gravür