Without doubt, such is the proportion from truth to falsehood as is that from light to darkness. And this truth is in itself of such excellence that, even though it extends over humble and lowly matters, it incomparably exceeds the uncertainties and falsehoods spread over great and lofty discourses. For our mind, even though it holds falsehood as its fifth element, this does not prevent the truth of things from being the highest nourishment of fine intellects, though not of wandering wits.

And falsehood is of such vileness that, even if it spoke well of great things of God, it takes away grace from His deity; and truth is of such excellence that, even if it praised the smallest things, they become noble. But you who live on dreams, you prefer the sophistic reasonings and cheats of speech in great and uncertain matters to the certain, natural ones that are not of such loftiness.

a b

c d

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g h

The incident motions with their reflex motions are of four kinds, of which one — the incident and reflex — is found to be rectilinear, having lines of equal obliquity; the other is also rectilinear, but the obliquities are various; the third has the incident motion rectilinear and the reflex curvilinear; the fourth has the incident motion curvilinear and the reflex of a straight line. Of these straight and curvilinear, each of them divides into two parts, because the first can have its rectilinear incident motion entirely opposite the chord of the arc made by the curvilinear reflex motion, and again that reflex arc can bend to the right or left of that rectilinear incident motion.

When the bird flies beating its wings, it does not extend the wings fully, because the wing-tips would be too remote from the lever and sinews that move them.

If in its descent the bird rows backward with those wings, the bird will move swiftly. And this happens because those wings strike the air that successively runs behind the bird to fill the vacuum from which it departs.