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MAGNETISM.

CONVERSATION I.

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

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

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James. Yes, it is called a loadstone, 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?

Tutor. Till then, they contented themselves with mere coasting voyages : seldom trusting themselves from the sight of land.

James. How long is it since this property 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 to 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 phagnet by being properly rubbed with the natural magnet, has a north end and a south end, called the north and south poles: to the former a mark is placed, for the purpose of distinguishing it.

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

Tutor. True; and if it were bound westerly 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

VOL. V.

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 wéather, which, in some latitudes, will last for many days together?

Charles. I did not think of that.

Tutor. Without the use of the magnet, no persons could have ventured upon such voyages as those to the West Indies, and other distant parts; the knowledge, therefore, of this instrument cannot be too highly prized.

James. Is that a magnet which is fixed to the bottom of the globe, and by means of which we set the

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