Inow lay this small magnet Fig. 29.) among them, and give the table a few gentle knocks, so as to shake the filings, and you observe in what manner they have ranged themselves about the magnet.

Charles. At the two ends or poles, the particles of iron form themselves into lines, a little sideways; they bend, and then form complete arches, reaching from some point in the northern half of the magnet to some other point in the southern half.-Pray how do you account for this?

Tutor. Each of the particles of iron, by being brought within the sphere of the magnetic influence, becomes itself magnetic, and possessed of two poles, and consequently disposes itself in the same manner as any other magnet would do, and also attracts with its extremities the contrary poles of other particles.

Ex. III. If I shake some iron filings through a gauze sieve, upon a paper that covers a bar magnet, the filings will become magnets, and will be arranged in beautiful

curves.

VOL. III.

R

James. Does the polarity of the magnet reside only in two ends of its surface?

Tutor. No one half of the magnet is possessed of one kind of polarity, and the other of the other kind; but the ends, or poles, are those points in which that power is the strongest.

DEF. A line drawn from one pole to the other is called the axis of the magnets

CONVERSATION XXV.

The Method of making Magnets-Of the Mariner's Compass.

TUTOR. I have already told you that artificial magnets, which are made of steel, are now generally used in preference to the real magnet, because they can be procured with greater ease, may be varied in their form more easily, and will communicate the magnetic virtue more powerfully.

Charles. How are they made?

Tutor. The best method of making artificial magnets is to apply one or more powerful magnets to pieces of hard steel,

taking care to apply the north pole of the magnet or magnets to that extremity of the steel which is required to be made the south pole, and to apply the south pole of the magnet to the opposite extremity of the ́piece of steel.

James. Has a magnet, by communicating its properties to other bodies, its own power diminished?

Tutor: No, it is even increased by it. -A bar of iron, three or four feet long, kept some time in a vertical position, will become magnetic, the lower extremity of it attracting the south pole, and repelling the north pole. But if the bar be inverted, the polarity will be reversed.

Charles. Will steel produce the same effects?

Tutor. It will not; the iron must be soft, and hence bars of iron that have been long in a perpendicular position, are generally found to be magnetical, as fire irons, bars of windows, &c.-If a long piece of hard iron be made red hot, and

then left to cool in the direction of the magnetical line, it usually becomes magnetical.

Striking an iron bar with a hammer, or rubbing it with a file, while held in this direction, renders it magnetical. An electric shock, and lightning, frequently render iron magnetic.

James. An artificial magnet you say is often more powerful than the real one; can a magnet, therefore, communicate to steel a stronger power than it possesses?

Tutor. Certainly not: but two or more magnets, joined together, may communicate a greater power to a piece of steel, than either of them possess singly.

Charles. Then you gain power according to the number of magnets made use of?

Tutor. Yes; very powerful magnets may be formed by first constructing several weak magnets, and then joining them together to form a compound one, and to act more powerfully upon a piece of steel.