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1. Magnets.-In order that the student may properly understand the fundamental facts concerning magnets and electric currents, he is recommended to try, or to witness, the simple experiments described in the succeeding pages, and as far as possible to verify for himself the truth of the statements made in the chapters of this short treatise.

Let him procure in the first place a sample of lodestone, the scientific name for which is Magnetite, some iron filings, a bundle of steel knitting needles, a skein of floss silk, some fine copper binding wire, a few iron nails, and also small screws of iron, steel, and brass. In addition include, if possible, one or two small pieces of metallic nickel and cobalt.

Lodestone or magnetite can be obtained from nearly all mineralogists or dealers in physical and chemical apparatus. Good specimens are sold generally for about 2s. 6d. or 5s. a pound. In choosing a sample, select a piece of an elongated shape, like a plum or large olive, and which picks up iron tacks or brads well at both ends. Two such pieces, at least, should be procured. They should be tested on purchasing, to see if they each will attract and pick up well a small iron screw or three or four iron tacks at each extremity.

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Magnetite or lodestone is an oxide of iron, or compound of iron and oxygen, having a chemical composition represented by the formula Fe3O4. It is very widely distributed in Nature in the earth's crust, and is found in masses or veins as a lustrous black or dull brown stone, in Sweden, Nova Scotia, Canada, Arkansas in the United States of America, and in many other places. It is found sometimes in enormous masses, forming beds or even entire mountains, and as an ore of iron, furnishes a source of very pure iron. It occurs also in New Zealand, Scotland, India and other localities, in a finely granular state known as iron sand, and this is also a source from which an excellent quality of iron may be extracted. It may be found frequently in crystals having a black lustre and an octagonal form, and it is the principal constituent in a non-magnetic state of the scale or oxide which is detached from iron when it is heated red-hot and forged under the hammer.

This ore of iron has been known for long ages past to be possessed in varying degrees of two remarkable properties which are called its Magnetic Properties. In the first place, if laid in iron filings, or in contact with small pieces of iron or magnetite, these last cling to it chiefly at certain points or edges of the mass which are spoken of as the poles of the lodestone.

The earliest mention, in English, of the attractive proper ties of magnetite, or the natural magnet, occurs in the writings of Alexander Neckam, in 1200 A.D. In 1269 a very full account of the chief facts known about it was given in a celebrated letter by Peter Peregrinus, or Peter the Pilgrim, a soldier monk serving in the army of Charles of Anjou, brother of Louis IX. of France. This letter, written in the trenches at the siege of Lucera, is remarkable for its complete statement of the facts of magnetic attraction. On the other hand, long before this date much knowledge of the properties of lodestone had been obtained by other nations. Early Phrygian iron miners, settled in Samothrace, an island in the Ægean Sea, were well acquainted with the attractive power of magnetite for iron. Priests of Samothrace, in 514 B.C., even sold magnetised iron

rings as a remedy for gout in the fingers, just as magnetic quacks retail various so-called magnetic remedial appliances today.

The second important fact with regard to this particular iron ore is, that if an elongated mass of it, having two well-defined poles at the extremities, is suspended by a thread or floated upon water in a little wooden cup, it always tends to place itself with the line joining the poles in a certain position with regard to the meridian of the place at which it is suspended, and if disturbed from that position it returns to it again. In the northern hemisphere of the earth, one pole of the lodestone sets itself approximately towards the north, and the other towards the south.

Let the reader take one of his pieces of magnetite, and having determined the position of the poles, suspend it by a few fibres of floss silk, so that it hangs with the line joining the poles in a horizontal position. It may conveniently be upheld by attaching the silk support to a little wooden stand. Verify then the following facts. If the suspended loadstone is dipped into iron filings, these cling on to it, chiefly at the poles, arranging themselves in little tufts. If another piece of lodestone is held near to the suspended one it will be found that each end or pole of the movable lodestone is differently acted upon by one selected pole or end of the fixed lodestone. Each pole of the fixed lodestone attracts one end of the movable one, and repels the other end of the movable. one. It is clear, therefore, that the two poles of the lodestone are not alike in properties, and their behaviour is summed up in the following law :

Similar poles Repel, Opposite poles Attract, understanding by the term similar poles, those that are found to be magnetically alike, and by opposite poles those that are not alike in a magnetic sense, when tested against the same pole of a third lodestone.

Dr. Gilbert, of Colchester, in his great book 'De Magnete ('On the Magnet') published in 1600 A.D., first suggested that

the earth as a whole is a great magnet, or acts as if it were one large lodestone, magnetised in an irregular manner. The tendency of the suspended lodestone at any place on the earth's surface to set its axis in a certain direction is merely due to the effort of the small lodestone to place its poles towards the dissimilar magnetic poles of the earth acting as a great lodestone. Hence we ought properly to call that end of the suspended lodestone which directs itself towards the north pole of the earth the south pole of the lodestone, because that northpointing end is a pole magnetically similar to the southern hemisphere of the earth.

To distinguish the lodestone poles they are generally called the North pole or North-seeking pole and the South pole or South-seeking pole, and they are also called sometimes the Red pole and the Blue pole, and distinguished by red and blue paint or paper placed on the poles. The student can recollect that Red corresponds to North, and BlUe to So Uth, by noting the way in which the letters R and U occur in the words Red and North, and Blue and South.

Hence the law of magnet attraction and repulsion is otherwise stated:

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The next fact of importance with regard to the magnetic properties of magnetite is that it can bestow them upon iron and steel when placed in contact with it.

Take a steel knitting needle, and having ascertained, by dipping the end of it in iron filings, that it is free from magnetism, stroke the knitting needle, say twenty times, over the pole of the lodestone with an action like a violin bow over the strings; but drawing the needle always one way, and not backwards and forwards. After so doing, test the knitting needle by dipping its ends in

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