is called a horny skin or covering, of the likeness of a horn; which is a clear covering. The third, uvea, of the likeness of a black grape. The fourth is called a cobweb. The first humour is called albuginous, from its likeness unto the white of an egg. The second glarial; that is, clear, like unto crystalline. The third vitreous, that is, clear as glass. And the diversity of humours causeth the diversity of the eyes.
Q. Why are men that have but one eye, good archers? and why do good archers commonly shut one? And why do such as behold the stars look through a trunk with one eye? A. This matter is handled in the perspective arts; and the reason is, as it doth appear in The Book of Causes, because that every virtue and strength united and knit together, is stronger than when dispersed and scattered. Therefore, all the force of seeing dispersed in two eyes, the one being shut, is gathered into the other, and so the light is fortified in him; and by consequence he doth see better and more certainly with one eye being shut, than when both are open.
Q. Why do those that drink and laugh much, shed most tears? A. Because that while they drink and laugh without measure the air which is drawn in doth not pass out through
the windpipe, and so with force is directed and sent to the eyes, and by their pores passing out, doth expel the humours of the eyes; which humour being expelled, brings tears.
Q. Why do such as weep much, urine but little? A. Because the radical humidity of a tear and of urine are of one and the same nature, and, therefore, where weeping doth increase, urine diminishes. And that they are of one nature is plain to the taste, because they are both salt.
Q. Why do some that have clear eyes see nothing? A. By reason of the oppilation and naughtiness of the sinews with which we see; for the temples being destroyed, the strength of the light cannot be carried from the brain to the eye.
Q. Why is the eye clear and smooth like glass? A. 1. Because the things which may be seen are better beaten back from a smooth thing than otherwise, that thereby the sight should strengthen. 2. Because the eye is moist above all parts of the body, and of a waterish nature; and as the water is clear and smooth, so likewise is the eye.
Q. Why do men and beasts who have their eyes deep in their head best see far off? A. Because the force and power by which we see is dispersed in them, and both go directly to the
thing which is seen. Thus, when a man doth stand in a deep ditch or well, he doth see in the daytime the stars of the firmament; because then the power of the night and of the beams are not scattered.
Q. Wherefore do those men who have eyes far out in their head not see far distant? A. Because the beams of the sight which pass from the eye, are scattered on every side, and go not directly unto the thing that is seen, and therefore the sight is weakened.