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magnet is called the, artificial magnet, and its use has entirely superceded that 'of the natural magnet. : This is because the artificial magnet can be made into a more convenient shape and given great- er magnet power. invention. The artificial magnet 1S. ait The discovery of the FIG, 2A BAR' MAGNET WITH IRON FILINGS ADHERING TO IT, natural magnet was possibly made through finding pieces of the loadstone attached to one another (small pieces to large pieces). It was centuries after this that it was discovered that such stones. had the still more remarkable property of pointing north and south when floated on a piece of wood. It was then that the pointing power .of the magnet or loadstone, was turned to advantage in navigation. the first device of this instrument. If a piece of loadstone or an artificial mag- net be fastened to a cork floating upon a basin..of water, it will, settle in a. north and, south direction; and, indeed, at the time of its introduc- tion into Europe, about the middle of the 13th century, it was all there was of the mariner's compass. experiment of floating a magnet on a cork or piece of wood and prove for himself this statement. : Magnetism.--Magnetism is that branch of physical. science which treats of the nature and properties of magnets and oftheir action on each other. The term magnetism is also used to designate the force which produces the effects called magnetic. - Magnetism is an invisible fluid without sensible weight, and so very subtle that it pervades all bodies capable of being magnetized. The term magnet - was given by the ancients to certain black stones found _in various parts of the world, notably at pLUE POLAR OF BARTHS MAG NET IS. _SHOWING HOW A BAR OF IRON BECOMES MAGNETIZED BY INDUCTION FROM THE > EARTH'S POLARITY. - Magnesia in Asia Minor, which possessed the property of attracting small pieces of iron and 'steel. as they deemed it, made the magnet stone famous; but it. was not until the tenth or twelfth century that such stones were discovered to have the still more The floating compass was in a short time, Anyone can try 'the - This magic property. THE Marine. REVIEW ~ remarkable property of pointing north and south when hung up by a thread. This property was turned to advantage in navigation. Its various names are in- teresting. In Pliny's time is was called ferrum (quick iron); the Chinese knew it as tchu-chy (the directing stone); and similarly in Swedish it is sequel-sten (the seeing stone); in Icelandic, lieder- stein (the leading stone), and "in Eng- lish the loadstone (from Sax., to lead). _ Every magnet whether natural or ar- tificial, has two poles and a neutral line. The poles, called north and south poles are at the extremities of the magnet and TRUE NORTH POLE | - | NO WP RGNE TIC POLES ee x a rl None oe) SHOWING HOW A BAR OF SOFT IRON HELD IN THE MAGNETIC 'MERIDIAN BECOMES. A _ MAGNET BY INDUCTION. ALSO HOW THE SAME BAR OF: IRON LOSES ITS: MAGNETISM WHEN HELD AT RIGHT ANGLES TO THE MAGNETIC MER- IDIAN. these portions are where the magnetic attraction is the greatest, and the neutral line or equator of the magnet will be about the center of the magnet. This is also called the dividing line, which sep- arates the north and south polarity, or magnetism, from each other. At the middle portion of the magnet there is no' nagnetic force, hence its name--neutral point. The natural magnet, called loadstone, is exceedingly rare, although closely re- lated to ore of iron, is of a dark gray color, and is found in Sweden, Norway, Spain, Arkansas and the Isle of Elba. What is known as an artificial magnet, _ towards the middle. is when a piece of steel, which has pes properly hardened' and tempered, rubbed with a piece of loadstone, or by another magnet, or when a current of electricity is passed around: it by means of a coil of insulated wire, it becomes a more or less powerful magnet. Arti- ficial magnets are permanent or tem- porary (depending on whether- the iron or steel is hard or soft) as they retain their magnetism after being #emoved from the source by which: they acquire it. The needles or bars of steel in the mar- iner's compass are artificial _ magnets. Artificial magnets have identically the same properties of the natural magnet-- two poles and a neutral line." _ The property of attracting iron is very 'unequally manifested at different points of the surface of the Magnet. Th tor example, an"' ordinary" bar-magnet be plunged in iron filings, these become ar- ranged around the ends of the bar in feathery tufts which decrease towards the middle, which is bare. If the magnet is very thick in proportion to its length, we may have filings adhering: to_all parts of it, but the quantity diminishes rapidly The middle portion where there is no visible magnetic force, and to which the filings refuse to ad- here, is the line of no magnetic force. Magnetic Needle--Any magnet freely suspended near its center of gravity is usually called a magnetic needle. One of its most usual forms is that of a very elongated rhombus of thin steel, having very near its center a concavity or cup, by means of which it can be belanced on a pivot. When it is thus balanced horizontally it does not, like an ordinary piece of matter, remain in equilibrium in all azimuths, but assumes one par- - ticular direction, to which it always comes back after displacement. In this position of equilibrium one of its ends points to magnetic north and the other to magnetic south, which differ in gen- eral by several degrees from geographi- cal, or true, north or south. This is the principle on which compasses are con- structed. | : Mutual Action of Poles--The two poles of a magnet appear identical when they are brought in contact with iron filings (see Fig. 2), but this identity is only: apparent, for on presenting one end of a magnet to one end of a needle thus balanced, we obtain either repulsion or attraction, according as the pole which is presented is similar or dissimilar to that to which it is presented. When a small magnetic needle is suspended by a fine thread, and the north pole of another needle is brought near its north pole, repulsion takes place. If on the contrary, the pole is brought near the south pole 'of a movable needle, the latter is strongly attracted. Hence, these two poles are not identical, for one is repelled