CONVERSATION XXIII.

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.

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?

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 diwection which the magnet takes.

Tutor. True; and if it were bound a Ivesterly 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 btained 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

weather, 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 East 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 globe in a proper direction with regard to the cardinal points, north, south, east, and west.

Tutor. That is called a compass, the needle of which being rubbed by the natural or real magnet, becomes possessed of the same properties as those which belong to the magnet itself.

Charles. Can any iron and steel be made magnetic ?

Tutor. They may ; but steel is the most proper for the purpose. Bars of iron thus prepared are called artificial magnets.

James. Will these soon lose the properties thus obtained?

Tutor. Artificial magnets will retain their properties almost any length of time, and since they may be rendered more powerful than natural ones, and can be made of any form, they are generally used, so that the natural magnet is kept as a curiosity.

Charles. What are the leading properties of the magnet?

Tutor. (1.) A magnet attracts iron. (2.) When placed so as to be at liberty to move in any direction, its north end points to the north pole, and its south end to the south pole that is called the polarity of the magnet. (3.) When the north pole of one magnet is presented to the south pole of another, they will attract one another. But if the two south, or the two north poles, are presened to each other, they will repel. (4.) When a magnet is so situated as to be at liberty to move any way, the two poles of it do not lie in an horizontal direction, it inclines one of its poles towards the horizon, and,