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INQUIRY RESPECTING THE MAGNET.
The magnet attracts powder of prepared steel, such as is used in medicines, and likewise steel reduced by calcination to a very fine black powder, as strongly as crude iron filings; but oxide of iron, which is an artificial rust of iron, it attracts more slowly and feebly. If however the iron be dissolved in aqua-fortis, and some drops of the solution be placed on a flat piece of glass, the magnet neither draws out the iron nor attracts the water in which it is dissolved.
The magnet attracts its own dust in the same way as iron filings ; and very small pieces of a magnet will attract one another, so as to hang in thin lines like needles.
Place the magnet at such a distance from the iron that it will not attract it. Put between them a cap of iron, still keeping the same distance, and the magnet will attract the iron; the power of the magnet being better diffused through the iron than through the medium of the air alone.
A magnet put into aqua-fortis, and left there for several hours, does not lose its power.
A magnet rubbed on cloth (as we do with amber),
or on another magnet, or warmed at the fire, is not increased in power.
One magnet has much more virtue than another ; and moreover if it be touched with iron, it will transmit its virtue in due proportion to the amount of it; the virtue, I say, not only of verticity, but likewise of simple attraction. For if you take a strong magnet and touch a piece of iron (say a knife) with it, and then touch another knife with a weaker magnet, you will see the iron touched by the stronger magnet attract a greater weight of iron than that touched by the weaker one.
A magnet attracts iron at an equal distance through air, water, wine, and oil.
If a magnet or its powder be immersed in aquafortis no solution at all takes place, as happens in iron; though the magnet appears to be a body of a similar substance to iron.
The powder of the magnet does not attract untouched iron, nor touched either; yet the powder is itself attracted by touched iron, and sticks to it; but not by untouched. So that the powder of the magnet appears to retain its passive virtue in some degree, but not its active.
A needle which, laid on a flat surface, is not attracted by the magnet by reason of its weight, will, if placed on the bottom of a glass turned up, so that it hangs over at each side, be attracted ; a fact which I think the more deserving of mention, because something of this kind may have given rise to the idle story that adamant hinders the power of the magnet. For place a needle upon a small piece of adamant cut into a square, with a magnet near, but not near enough to
draw it, yet it will tremble. But this trembling is not the prevention of motion, but the motion itself.
A magnet attracts touched iron far more vigorously than untouched; so that the iron, which untouched is not attracted at a given distance, will, if touched, be attracted at thrice that distance.
No iron or metallic matter is extracted from the magnet by fire, or any known means of separation.
A magnet is not dissolved in nitro-muriatic acid any. more than in aqua-fortis.
A magnet put into a crucible, yet without any flame, is diminished much in weight, and immensely in power, so as scarce to attract iron.
A magnet hardly turns liquid, but yet it changes its shape a little, and becomes red hot as iron.
A magnet burnt whole retains its passive power, so as to cling to another magnet; but almost loses its active power of attracting iron.
A magnet burnt in a crucible emits a fume, though it be scarcely visible, which will somewhat whiten a sheet of brass laid over it; as likewise do metals.
A magnet in the process of burning penetrates through the crucible, and that too whether it be broken outside or inside, which makes it shine with brilliancy.
All agree that if a magnet be burned to such an extent as to throw out a lurid and sulphureous flame it entirely loses its virtue, and never afterwards recovers it, though it be cooled in a position south and north; an operation which gives virtue to bricks, and renews the power of magnets not completely burnt.
An experiment has been made with magnetised