If a small helix, or coil of covered wire, is arranged with an unmagnetized steel needle within it, so that the discharge of a large Leyden jar may take place through the coil, the needle will be found strongly magnetic after the discharge of the electricity. (Fig. 194.) Many years before this was known, it had been noticed that when a ship was struck by lightning, the compasses were generally reversed; and in a special case, where a house was struck, the electricity entered a box of knives, fusing some, tearing the handles off others, but leaving them strongly magnetic. Electricians tried to repeat the effect by sending the discharge of powerful Leyden batteries through bars of steel without any important result; and it was not until Oersted, in the year 1819, made his important discovery that the copper wire conveying the electricity possessed peculiar magnetic power, that the principle began to be understood, and then the electricians succeeded in imitating the effects of lightning on steel, as already described in the beginning of this chapter. (Fig. 194.)

When the electricity has passed away from the Leyden jar through the coil of copper wire, it no longer possesses any power to affect a piece of steel or iron, but if the wires of the voltaic battery are now connected with the coil of copper wire, which should be covered with cotton or silk, and many yards in length, then a bar of steel or soft iron is not only rendered magnetic, but remains permanently so, as long as the current of electricity continues to pass along the coil of wire, so that if some nails or iron filings are brought to the bar of iron, one end of which projects from the coil, they cling to it with great force, and a great number of nails may be hung on in this manner, but they immediately fall off when the contact is broken with the battery. (Fig. 195.)

Electricity thus becomes a source of magnetism, and the discoverer, Oersted, found that only needles or bars of steel or iron were thus affected, and not those of brass, shell-lac, sulphur, and other substances; he termed the conducting wire "a conjunctive wire," and described the effect of the electric current or "electric conflict," as he called it, as resembling a Helix (from ???ss?, to turn round; a screw or spiral), and that it is not confined to the conducting wire, but radiates an influence at some distance. This latter statement is exactly in accordance with our present notions, and hence the coil conveying the current is said to induce magnetism in the iron or steel, just as the phenomena of induction are produced with frictional electricity. The effect of Oersted's discovery, says Silliman, was truly electric; the scientific world was ripe for it, and the truth he thus struck out was instantly seized upon by Arago, AmpÈre, Davy, Faraday, and a crowd of philosophers in all countries. The activity with which this new field of research has been cultivated, has never relaxed even to this hour, while it has borne fruit in a multitude of theoretical and practical truths, and above all, in the electro-magnetic telegraph, truly called, and especially in connexion with the Atlantic telegraph wire, "the great international nerve of sensation."

Magnetism is not only the result of a current of electricity through any good conductor, but there are certain oxides of iron, called magnetic iron ores, which have the property of attracting iron filings, and are mostly found in primitive rocks, being abundant at Roslagen, in Sweden, and called the loadstone, from its always pointing, when freely suspended, to the Polar, North, or Load Star. If a tolerably large specimen of this mineral is examined, there will be found usually two points where the iron filings are attracted in larger quantities than in other parts of the same specimen. These attractive points are called poles, and the loadstone being properly mounted with soft iron bars, termed cheeks, bound round it (in old-fashioned loadstones) with silver plate and duly ornamented with engraving, has its magnetic power greatly increased, and is then said to be endowed with magnetic polarity; and to prevent the loss of power, a soft piece of iron, called the armature, is placed across and attracted to the poles of the loadstone. (Fig. 196.)

Second Experiment.

If a needle of tempered steel (fitted with a little brass cup in the centre to work upon a point) is rubbed with the loadstone in one direction only, it is rendered permanently magnetic, and will now be found to take a certain fixed position, pointing always in a direction due north and south. The end which points towards the north is called the north pole, and the other extremity the south pole, and it is usual to mark the north pole with an indent or scratch to distinguish it at all times.

Third Experiment.

If another bar of steel is magnetized, and the north pole duly marked, and then brought towards the same pole of the suspended magnet, instant repulsion takes place; the magnet, of course, grasped in the hand is not free to move, but the small magnet immediately shows the same fact noticed with electricity, viz., "that similar magnetisms repel." Two north poles repel each other, but when the bar of steel is reversed, the opposite effect occurs, and the suspended magnet is attracted, showing that dissimilar magnetisms attract, and a north will attract a south pole. (Fig. 197.)

Fourth Experiment.

By contact, the magnetic power is transferred from the magnet to a piece of unmagnetized steel, and it is stated that the highest magnetizing effect is that produced by the simple method of Jacobi. A horse-shoe magnet has its poles brought in contact with the intended poles of another bar of steel, likewise bent in the form of a horse-shoe, and by drawing the feeder over the unmagnetized horse-shoe in the direction of the arrow in the cut, and when it reaches the curve, bringing it back again to the same place, say at least twelve times, and after turning the whole over without separating the poles, and repeating the same operation on the other side likewise twelve times, the steel is then powerfully magnetized; and it is said that a horse-shoe of one pound weight may be thus charged so as to sustain twenty-six and a half pounds, and that by the old method of magnetizing it would only have sustained about twenty-two pounds. (Fig. 198.)

Fifth Experiment.

If the horse-shoe magnet is placed on a sheet of paper, and some iron filings are dusted between the poles, a very beautiful series of curves are formed, called the magnetic curves, which indicate the constant passage of the magnetic power from pole to pole.

Sixth Experiment.

The magnetic force exerted by a horse-shoe-shaped piece of soft iron, surrounded with many strands of covered copper wire in short lengths, is extremely powerful (Fig. 199), and enormous weights have been supported by an electro-magnet when connected with a voltaic battery. Supposing a man were dressed in complete armour, he might be held by an electro-magnet, without the power of disengaging himself, thus realizing the fairy story of the bold knight who was caught by a rock of loadstone, and, in full armour, detained by the unfriendly magician.

a. Powerful electro-magnet supporting a great weight. b. The battery.

Seventh Experiment.

When a piece of soft iron is held sufficiently near one of the poles of a powerful magnet, it becomes by induction endowed with magnetic poles, and will support another bit of soft iron, such as a nail, brought in contact with it. When the magnet is removed, the inductive action ceases, and the soft iron loses its magnetic power. This experiment affords another example of the connexion between the phenomena of electricity and magnetism. It is in consequence of the inductive action of the magnetism of the earth that all masses of iron, especially when they are perpendicular, are found to be endowed with magnetic polarity; hence the reaction of the iron in ships upon the compasses, which have to be corrected and adjusted before a voyage, or else serious errors in steering the vessel would occur, and there is no doubt that many shipwrecks are due to this cause. No other metals beside iron, steel, nickel, cobalt, and possibly manganese, can receive or retain magnetism after contact with a magnet.

The remarkable effect of magnetism upon all matter, so ably investigated by Faraday and others, will be explained in another part of this book—viz., in the article on Dia-Magnetism.

Magician and his loadstone-rock.—Vide Fairy Tale.