In the celebrated OPTICS, the visual lines are mistaken for rays of light radiated from the flame, and reflected from the other objects; which rays are supposed to enter the eye, and (as if possessed of intelligence) arrange themselves on the back of the eye or on the retina, in the precise form, but of a different size, of the object to which the eyes are directed, as the means by which externals are seen before the face. In cases wherein the visual line is indirect, as when lying through media of unequal density, the supposed rays are said to be refracted: and, because the curtained iris excludes the visual medium, except through the pinhole pupil, thence along the axis through the lenses of the eyeball, the _optics_ inculcate, that the eye has been formed to see only in straight lines. Finally, by Dr. Reed it is taught, that the use of the sensation and of the image on the _back_ of the eye, is to make the external object _opposite the face_ be seen; all which has to be rejected and forgotten in being guided by the natural, real function of the sense, against which there is no appeal. There are no rays concerned; the medium of vision is quiescent; there can be neither radiation, reflection, nor refraction effected by passive inert bodies; there is no image on any part of the eye or retina; and externals could not be made visible, or seen by their images. Such absurdities, all of which are maintained in modern philosophy, have prevented, more than any thing else, the science and phenomena of Mesmerism being understood.