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MAGNETISM

VOL. 111

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of the Magnet: its Properties ; useful to Mariners, and others; Iron rendered Magnetic; Properties of the Magnet.

TUTOR. You see this dark-brown min. eral body, it is almost black, and you know it has the property of attracting needles and other small iron substances.

James. Yes, it is called a load-stone, leading-stone, or magnet; we have often been amused with it: but

you

told us that it possessed a much more important property than that of attracting iron and steel.

Tutor. This is what is called the directive property, by which mariners are enabled

to conduct their vessels through the mighty ocean out of the sight of land: by the aid of this, miners are guided in their subterranean inquiries, and the traveller through deserts otherwise impassable.

Charles. Were not mariners unable to make long and very distant voyages till this property of the magnet was discovered? i Tutor. Till then, they contented them selves with mere coasting voyages; seldom trusting themselves from the sight of land.

James. How long is it since this proper. ty of the magnet was first known?

Tutor. About five hundred years; and it is not possible to ascertain, with

any

degree of precision, to whom we are indebted for this great discovery.

Charles. You have not told us in what the discovery consists.

Tutor. When a magnet, or a needle rubbed with a magnet, is freely suspended, it will always, and in all places, stand nearly north and south.

Charles. Is it known which end points to the north, and which the south?

Tutor. Yes: or it would be of little use : each magnet, and each needle, or other piece of iron, that is made an artificial magnet by being properly rubbed with the nautral magnet, has a north end and a south end, called the north and south poles : to the former a

s mark placed, for the purpose of distinguishing it.

James. Then if a ship were to make a voyage to the north, it must follow the disection which the magnet takes.

Tutor. True ; and if it were bound a J.vesterly course, the needle always pointing north, the ship must keep in a direction at right angles to the needle. In other words, the direction of the needle must be across the ship.

Charles. Could not the same object be obtained by means of the pole star?

Tutor. It might, in a considerable degree, provided you could always ensure a fine clear sky; but what is to be done in cloudy

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