When the electricity has passed away from the Leyden jar through the coil of [Page 207] 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 [Greek: _helissô_], 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_." [Illustration: Fig. 196. A loadstone mounted in brass or silver, with the iron cheeks B B attached. C. The bit of soft iron called the armature.]