once a powerful magnet--so much so, that I should not wonder if these magnetic needles on different parts of the table pointed to it. And I will shew you by another experiment what an attraction it has. This piece and that piece of iron, and many other pieces, are now strongly attracted (fig. 52); but as soon as I break contact, the power is all gone, and they fall. What, then, can be a better or a stronger proof 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 shew you better than such an experiment as this the magnetic attraction with which we have endowed these portions of iron? Here, again, is a fine illustration of this strong power of magnetism. It is a magnet of the same sort as the one you have just seen. I am about to make the current of electricity pass through the wires which are round this iron for the purpose of shewing you what powerful effects we get. Here are the poles of the magnet; and let us place on one of them this long bar of iron. You see, as soon as contact is made, how it rises in position (fig. 54); and if I take such a piece as this cylinder, and place it on, woe be to me if I get my finger between: I can roll it over, but if I try to pull it off, I might lift up the whole magnet; but I have no power to overcome the magnetic power which is here evident. I might give you an infinity of illustrations of this high magnetic power. There is that long bar of iron held out; and I have no doubt that, if I were to examine the other end, I should find that it was a magnet. See what power it must have to support not only these nails but all those lumps of iron hanging on to the end. What, then, can surpass these evidences of the change of chemical force into electricity, and electricity into magnetism? I might shew you many other experiments whereby I could obtain electricity and chemical action, heat and light, from a magnet; but what more need I shew you to prove the universal correlation of the