Treasury of Optics

the vision. And we find again that the colors of bodies of iron-color, when strong light rises upon them, become clearer. And we find also that, when strong light rises upon dense white bodies, they are increased in whiteness and sparkling to the sense. And we find again that transparent bodies colored with strong colors, such as strong red, which are in transparent vessels, when they are in dark places and weak lights, appear black and dark, and as if they were not transparent, and when they are in strong lights, and the light of the sun has risen upon them, their colors become clear, and transparency appears in them. And similarly, the colors of transparent colored stones, when they are in dark places, appear turbid and dark: and when strong light rises upon them, or they are placed in opposition to light, so that the light passes through them, their colors appear clear, and transparency appears in them because of the penetration of light. And again, when transparent colored bodies are placed in opposition to light: and a white body is placed on the side opposite the light, as we said above: and if the light is strong: the form of that color will appear in its shadow upon the white body placed opposite to it: and if the light rising upon it is weak, only the shadow will appear upon the white body opposite to it, and the color will not appear. And again we find that the feathers of a peacock, and the cloth that is called amilialmon a type of shot silk, iridescent green and pink, are diversified in color to the vision in different times of the day, according to the diversity of the light rising upon them. These arrangements appearing in colors signify, therefore, that the colors of colored bodies are not perceived by the vision, except according to the lights rising upon them. And since the strong lights of visible things sometimes conceal certain things that are in certain visible things, and sometimes manifest to us certain things that are in certain visible things: and the weak lights of visible things sometimes manifest certain things that are in certain visible things, and sometimes conceal certain things that are in certain visible things: and the colors of colored bodies are sometimes altered according to the diversity of the light that rises upon them: and strong lights rising upon the vision itself sometimes prohibit the vision itself from the perception of certain visible things: and the vision, however, in all these things, perceives nothing of the visible things unless the form is illuminated. Therefore, what the vision perceives from a seen thing is only according to the light that is in that seen thing, and according to the lights that rise upon the vision itself in the perception of that visible thing, and upon the air between the vision and the seen thing. Why, indeed, strong lights prohibit the vision from the perception of certain visible things will be declared by us in our discourse on the quality of vision.

CONCERNING THE COMPOSITION OF THE EYE, ITS FORM AND SITUATION. Chapter Four.

A large decorative initial 'O' features floral scrollwork.
The eye is composed of various tissues and bodies: and its beginning and growth is from the anterior part of the brain: since from the anterior part grow two similar optic nerves, and they begin to arise from two places from the two parts of the anterior brain: and it is said that each of them has two tunics, and that they grow from two tissues of the brain, and they arrive at the middle of the exterior part of the brain and the anterior brain, then they meet and make one optic nerve: then this nerve is divided, and two equal and similar optic nerves are made again: then these two nerves are extended, until they arrive at the two convexities of the two concave bones containing the two eyes: and in the two middles of these two concave bones are two holes equally perforated: and their situation in the common nerve is a situation similar to that. Therefore, the nerves enter these two holes, and exit to the concavities of the two bones, and there they are dilated and widened, and the extremity of each of them is made like an instrument for pouring wine into casks: and each of the eyes is composed upon this extremity of the nerve, which is the aforesaid instrument, and is consolidated with it: and the situation of each of the eyes from the common nerve is a similar situation. And the whole of each eye is composed of many tunics. The first of them, therefore, is the white fat, which fills the concavity of the bone: and it is the greatest part of the eye: and it is called the consolidativa sclera. And within this fat is a round sphere, concave, black for the most part, and green, and glaucous in certain eyes: and the body of this sphere is thin, and furthermore dense and not rare: and its manifestation is applied with the consolidativa sclera: and inside it is a concavity: and in the part of the concavity there is as it were a certain rubbing: and as the consolidativa sclera contains this sphere, except for its anterior part: since the consolidativa sclera does not cover the anterior of this sphere, but circles over its anterior: and this tunic is called the uuea uvea/iris, because it is likened to a grape. And in the middle of the anterior of the uuea uvea is a round hole perforated up to its concavity: and it is opposite to the extremity of the concavity of the nerve, upon which the eye is composed. And this hole, and the whole anterior of the uuea uvea, in whose circuit the consolidativa sclera circulates, is covered externally by a strong, white, transparent tunic: and it is called the cornea, because it is likened to white and clear horn. And within the concavity of the uuea uvea is a white, small, moist sphere, receptive of the moisture of visible forms: and in it is transparency, not intensely great, but some thickness: and its transparency is likened to the transparency of ice: and therefore it is called the glacialis crystalline lens: and it is composed upon the extremity of the concavity of the nerve: and in the interior of this sphere there is a small superficial compression, and it is likened to the compression of the surface of a lentil: the surface of its anterior, therefore, is a portion of the surface of a sphere, greater than the spherical surface, containing its two holes: and this...