A magician of former days had a figure of a swan, which floated on a vessel of water, round the rim of which were placed the twenty-four letters of the alphabet. Addressing the spectators, he was accustomed to ask for a name to be given him, and it was correctly spelt by the swan, as it moved from one letter to another till it had indicated the whole. A little philosophy, in this instance, produced repeatedly great astonishment. A magnetic bar was placed in the swan, and the performer had a powerful magnet concealed in his own dress, and the swan, of course, followed his motions. Thus, if he wanted the swan to spell “Selina,” he moved first to S, then to E, and so on, through the successive letters of that name, till the word was spelt. On one occasion, however, the performer was not a little disconcerted--the swan stopped in its course and refused to move. Again and again the effort was made, but it was utterly in vain; the magician could only acknowledge that some person was in the room aware of his secret, and counteracting his movements. Sir Francis Blake Delaval avowed himself to be the person: he produced a magnet which he had used on facing the performer as he stood at the table; the swan was, therefore, placed between two attractive instruments, and, of course, remained immovable. A magnet may be described as a piece of iron, which possesses the property of turning towards the poles of the earth. This extraordinary quality does not necessarily belong to all specimens of iron in its native state, but only to one kind or variety called the oxide, on account of its union with oxygen in a particular condition. The possession of a special quality in this ore of iron was not discovered from its polarity, or power of turning to the poles of the earth, but from its property of attracting small pieces of iron, which are not magnetic; and hence it was called the loadstone.