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 magnet 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 a 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.

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 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 presented 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 a horizontal direction, it inclines one of its poles towards the horizon, and of course, elevates the other pole above it; this is called the inclination or dipping of the magnet. (5.) Any magnet may be made to impart its properties to iron and steel.

CONVERSATION XXIV.

Magnetic Attraction and Repulsion.

Tutor. Having mentioned the several properties of the magnet or loadstone, I intend, at this time, to enter more particularly into the nature of magnetic attraction and repulsion. Here is a thin iron bar, eight or nine inches long, rendered magnetic, and on that account it is now called an artificial magnet: I bring a small piece of iron within a little distance of one of the poles of the magnet, and you see it is attracted or drawn to it.

Charles. Will not the same effect be produced, if the iron be presented to any other part of the magnet?

Tutor. The attraction is strongest at the poles, and it grows less and less in proportion to the distance of any part from the poles, so that in the middle, between the poles, there is no attraction, as you shall see by means of this large needle.

James. When you held the needle near the pole of the magnet, the magnet moved to that, which looks as if the needle attracted the magnet.

Tutor. You are right: the attraction is mutual, as is evident from the following experiment. I place this small magnet on a piece of cork, and the needle on another piece, and let them float on water, at a little distance from each other, and you observe that the magnet moves towards the iron, as much as the iron moves towards the magnet.

Charles. If two magnets were put in this situation, what would be produced?

Tutor. If poles of the same name, that is, the two north, or the two south, be brought near together, they will repel one another; but if a north and south pole be presented, the same kind of attraction will be visible, as there was between the magnet and needle.

James. Will there be any attraction or repulsion if other bodies, as paper, or thin slips of wood, be placed between the magnets, or between the magnet and iron?

Tutor. Neither the magnetic attraction nor repulsion is in the least diminished, or in any way affected by the interposition of any kind of bodies, except iron. Bring the magnets together within the attracting or repelling distance, and hold a slip of wood between them: you see they both come to the wood.

Charles. You said that iron was more easily rendered magnetic than steel, does it retain the properties as long too?

Tutor. If a piece of soft iron, and a piece of