2920. Light does not stream into the eye like water into the sponge, but it progresses gradually into and operates upon it.
2921. The eye, in order to experience the sensation of light, is placed in a similar tension to the air, water, or crystal. This tension between it and the brain is perceived by the latter as illumination. The eye is a prism, in which the brain sees the world, in which the brain observes its own tension, or the production of colour. Sight is a deoxydation of the eye.
2922. The optic nerve is an organized ray of light, the brain an organized sun, the eye an organized chromatic sun or rainbow.
2923. Just as the sonorous figures are delineated in the ears, and as the nerve perceives these, but not any concussion of the air; so also does the optic nerve perceive not the light in general, but its terrestrial formation or the chromatic image, which has been propagated into the eye.
2924. In an eye, while seeing, the world is depicted; as in the ear, when hearing, the crystalline forms of the air are delineated.
2925. The eye does not on that account see two worlds. For the chromatic image is nothing else than that which is external to or without the eye. It is verily one and the same influence of light, which acts continuously in a straight line between the chromatic image and the object apparent or beheld.
2926. As a stick thrusts us from the side whither it comes; so does the chromatic image from the side whence the light comes. The exit and entrance of the light are not distinct from each other. The objects could not therefore appear reversed, because we do not see the image in the eye, but feel its process of deoxydation along with its direction.
2927. The objects of the eye are colours. Like as they are related in nature, so also must they be in sight; for they are only the eye extended, or this again is only the formed colour.
2928. We see nothing else but colours, no bodies. For the eye there is no material world. It directly perceives the spirit, and indeed its own spirit, or the world of light.
2929. There is no pre-established harmony, but complete conformity between the world and organ of sense. (Vid. Oken's Essays, "Ueber das Universum als fort-gesetztes System der Sinne," and "Erste Ideen zur Theorie des Lichts." Jena bei Fromann, 1808.)