thereof and
purge them: and, in the absence of the sun, those humours become dark
and black, and the sight not so good.

Q. Why does the blueish grey eye see badly in the day-time and well in
the night? A. Because greyness is light and shining in itself, and the
spirits with which we see are weakened in the day-time and strengthened
in the night.

Q. Why are men's eyes of diverse colours? A. By reason of diversity of
humours. The eye hath four coverings and three humours. The first
covering is called consolidative, which is the outermost, strong and
fat. The second 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 l