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than this of the relation of the powers of magnetism and electricity? Again, here is a little piece of iron which is not yet magnetised. It will not at present take up any one of these nails; but I will take a piece of wire and coil it round the iron (the wire being covered with cotton in every part it does not touch the iron), so that the current must go round in this spiral coil—I am, in fact, preparing an electro-magnet (we are obliged to use such terms to express our meaning, because it is a magnet made by electricity,—because we produce by the force of electricity a magnet of far greater power than a permanent steel one). It is now completed and I will repeat the experiment which you saw the other day, of building up a bridge of iron nails; the contact is now made and the current is going through; it is now a powerful magnet; here are the iron nails which we had the other day, and now I have brought this magnet near them they are clinging so hard that I can scarcely move them with my hand (fig. 53). But when the contact is broken, see how they fall. What can show you better than such an experiment as this the magnetic attraction with which we have endowed these portions of iron?