Now, there are some curious bodies in nature (of which I have two specimens on the table) which are called _magnets_ or _loadstones_--ores of iron, of which there is a great deal sent from Sweden. They have the attraction of gravitation, and attraction of cohesion, and certain chemical attraction; but they also have a great attractive power, for this little key is held up by this stone. Now, that is not chemical attraction,--it is not the attraction of chemical affinity, or of aggregation of particles, or of cohesion, or of electricity (for it will not attract this ball if I bring it near it); but it is a separate and dual attraction--and, what is more, one which is not readily removed from the substance, for it has existed in it for ages and ages in the bowels of the earth. Now, we can make artificial magnets (you will see me to-morrow make artificial magnets of extraordinary power). And let us take one of these artificial magnets, and examine it, and see where the power is in the mass, and whether it is a dual power. You see it attracts these keys, two or three in succession, and it will attract a very large piece of iron. That, then, is a very different thing indeed to what you saw in the case of the shell-lac; for _that_ only attracted a light ball, but here I have several ounces of iron held up. And if we come to examine this attraction a little more closely, we shall find it presents some other remarkable differences: first of all, one end of this bar (fig. 37) attracts this key, but the middle does not attract. It is not, then, the _whole_ of the substance which attracts. If I place this little key in the middle, it does not adhere; but if I place it _there_, a little nearer the end, it does, though feebly. Is it not, then, very curious to find that there is an attractive power at the extremities which is not in the middle--to have thus in one bar two places in which this force of attraction resides! If I take this bar and balance it carefully on a point, so that it will be free to move round, I can try what action this piece of iron has on it. Well, it attracts one end, and it also attracts the other end, just as you saw the shell-lac and the glass did, with the exception of its not attracting in the middle. But if now, instead of a piece of iron, I take a _magnet_, and examine it in a similar way, you see that one of its ends _repels_ the suspended magnet--the force then is no longer attraction, but repulsion; but if I take the other end of the magnet and bring it near, it shews attraction again. [Illustration: Fig. 37. and Fig. 38.]