THE above facts show plainly that optical illusions find their source in the very mechanism of the organs of sight, and that without going farther than the eye itself we may discover numberless examples of these phenomena. We shall presently bring before our readers the innumerable means devised by art for deceiving the sense of sight and impressing us with sensations that are purely imaginary. But before describing these numerous pieces of apparatus we must still remain for a short time within the domain of man’s faculties, and describe some of the illusions that we are subjected to by those powers of the imagination that are supposed to hold in check the five senses of the body. Our imagination, however, plays us as many tricks as our eyes, and, like them, is alternately false and true. Touch, taste, smell, hearing, and sight, are all supposed to be under its powerful influence for good or evil; but they are all deceived by it in turn, more especially the sense of sight, which we generally boast of as being the most trustworthy of them all. Were we to describe all the labyrinths into which our imagination is continually leading us, we might easily extend this little volume to one of treble the size. But our purpose is not so much to write a history of all the hallucinations to which the imagination is subject, but to cull from those already existing the most interesting instances in which this great faculty is alternately the victim and the tyrant of the sense of sight. Amongst many works on this subject we may cite that of Brière de Boismont on “Hallucinations, Apparitions, Visions, &c.,” from which we shall draw largely in the following pages. The examples we shall give will be those only in which the victims of the hallucination were in the full enjoyment of their mental faculties, and could healthily analyze the sensations and impressions to which they were subjected. One of the first of these bears upon those diseases of the eye to which allusion was made in Chapter IV. Towards the end of 1833, a poor washerwoman who was tormented grievously with rheumatic pains gave up her business, and took to sewing for her livelihood. Being but little accustomed to this kind of work, she was compelled to sit over her needle late at night in order to save herself from starving. The unwonted strain upon the eyes soon brought on ophthalmia, which speedily became chronic. Nevertheless, she continued her work, and fell a prey to _diplopia_, or double sight in each eye. Instead of a single needle and thread, she saw four continually at work, everything else about her being similarly multiplied. At first she took no notice of the singular illusion, but at last both imagination and sight joined arms against the judgment, and the poor creature imagined that Providence had taken pity on her forlorn condition, and had worked a miracle in her favour by bestowing on her four pair of hands in order that she might do four times her usual amount of work.