This uncertainty with respect to the direction of sound is the foundation of the art of ventriloquism. If we place ten men in a row at such a distance from us that they are included in the angle within which we cannot judge of the direction of sound, and if in a calm day each of them speaks in succession, we shall not be able with closed eyes to determine from which of the ten men any of the sounds proceed, and we shall be incapable of perceiving that there is any difference in the direction of the sounds emitted by the two outermost. If a man and a child are placed within the same angle, and if the man speaks with the accent of a child without any corresponding motion in his mouth or face, we shall necessarily believe that the voice comes from the child; nay, if the child is so distant from the man that the voice actually appears to us to come from the man, we shall still continue in the belief that the child is the speaker; and this conviction would acquire additional strength if the child favoured the deception, by accommodating its features and gestures to the words spoken by the man. So powerful, indeed, is the influence of this deception, that if a jack-ass, placed near the man, were to open its mouth, and shake its head responsive to the words uttered by his neighbour, we should rather believe that the ass spoke than that the sounds proceeded from a person whose mouth was shut, and the muscles of whose face were in perfect repose. If our imagination were even directed to a marble statue or a lump of inanimate matter, as the source from which we were to expect the sounds to issue, we would still be deceived, and would refer the sounds even to these lifeless objects. The illusion would be greatly promoted, if the voice were totally different in its tone and character from that of the man from whom it really comes; and if he occasionally speaks in his own full and measured voice, the belief will be irresistible that the assumed voice proceeds from the quadruped or from the inanimate object.