Page:World of Wonders, The (1873?, Cassell, Petler, and Galpin).djvu/19

 drawn to the magnet, while there are some which are repelled; but the action with all, save iron, is so feeble that we may dismiss them from our consideration.

Pursuing our investigations with substances of an iron nature, we shall find that only one of the iron ores which occurs in the earth's crust in any quantity is attracted by the magnet. This is very singular, because a piece of kidney iron ore is so

solid and heavy that the inexperienced would at once pronounce it to be iron, and yet it has not the slightest effect on a magnetised needle. The one ore thus influenced is the best of the iron ores; from it is reduced the celebrated Swedish iron. It is the lodestone, every molecule of which is composed of three atoms of iron and four atoms of oxygen. Magnetism seems first have been observed in lodestone which was found near the town of Magnesia, in Asia Minor, and from the name of the town came the name of the property the ore possessed. How the ore became possessed of its property we shall in our next paper learn.

The experiments, and who performed them, by which it was discovered that the peculiarity of the lodestone could be imparted to iron, are lost in the

mists of distant times. But long before even this the Chinese had a knowledge of magnetism; it is said they have had compass needles for 3,000 years. We have long since given up using the lodestone for producing magnets, and now we can multiply magnets from any single magnet ad libitum.

The process is simple enough. Take a knitting-needle and pass it over the ends of a magnet, being careful to bring the end of the needle upon one leg of the magnet first, then slowly slide it to the other, and so pass the whole needle over the poles or ends of the magnet, and repeat this eight or ten times. Or the needle may be laid upon a table, the magnet placed upon it as in Fig. i. The magnet must be placed down upon the centre of the needle, and slid backwards and forwards quite to the end of the needle each time; and the magnet must be removed when at the place where it first touched the needle. If instead of a needle a piece of iron wire were used, it would be found that as soon as the magnet were removed the wire would lose its magnetism, because soft iron is incapable of permanent magnetisation—of steel alone can permanent magnets be made. Now take the needle which you have magnetised, and dip it in some iron-filings. If you have "touched" it properly, you will find that the filings gather in clusters near the ends, seeming to show that the magnetic power is concentrated there; very probably the filings will also be found in bundles at several intermediate points—these places are termed "consecutive poles," and prove that the needle has been badly "touched."

But what has the needle acquired? Not weight—it weighs precisely the same before and after the touching. No magnetism has left the horseshoe, for, singular to say, it is a stronger magnet, most probably, for having magnetised the needle.

Another peculiar fact may be easily ascertained. From the accumulation of filings at the extremities of the needle, it might be supposed that the magnetism had concentrated there; but if now the needle be broken into two or three pieces, and each piece dipped in the filings, the filings cluster at the ends of each piece, just as they did in the whole needle, showing that whatever magnetism is it is not a fluid, like electricity, which can run about and accumulate here or there. And while we have the filings at hand, take a piece of cardboard or stiff paper, and placing it upon the poles of the horse-shoe; sift the filings over it, and by gently tapping the paper they will arrange themselves as in Fig. 2; and if the magnet be moved beneath the paper, the filings will rise and fall as if an unseen wave passed through them; and a little observation will convince you that there are curved lines of magnetic action passing from one pole to the other, and the filings really follow these curves.

The magnetic atmosphere which surrounds the poles has more powers than iron filings can make apparent. found that there is always amongst fifteen or twenty persons one at least who can feel a very singular sensation when a strong magnet is moved down the back without