But why should thunderbolts, whether stone axes or flint arrowheads, be preserved, not merely as curiosities, but from motives of superstition? The reason is a simple one. Everybody knows that in all magical ceremonies it is necessary to have something belonging to the person you wish to conjure against, in order to make your spells effectual. A bone, be it but a joint of the little finger, is sufficient to raise the ghost to which it once belonged; cuttings of hair or clippings of nails are enough to put their owner magically in your power; and that is the reason why, if you are a prudent person, you will always burn all such off-castings of your body, lest haply an enemy should get hold of them, and cast the evil eye upon you with their potent aid. In the same way, if you can lay hands upon anything that once belonged to an elf, such as a fairy-bolt or flint arrowhead, you can get its former possessor to do anything you wish by simply rubbing it and calling upon him to appear. This is the secret of half the charms and amulets in existence, most of which are either real old arrowheads, or carnelians cut in the same shape, which has now mostly degenerated from the barb to the conventional heart, and been mistakenly associated with the idea of love. This is the secret, too, of all the rings, lamps, gems, and boxes, possession of which gives a man power over fairies, spirits, gnomes, and genii. All magic proceeds upon the prime belief that you must possess something belonging to the person you wish to control, constrain, or injure. And, failing anything else, you must at least have a wax image of him, which you call by his name, and use as his substitute in your incantations.