The Book of the science of Mechanics must precede the Book of useful inventions.

Necessity is the mistress and guide of nature.

I roamed the countryside searching for the answers to things I did not understand. Why shells existed on the tops of mountains along with the imprints of coral and plant and seaweed usually found in the sea. Why the thunder lasts a longer time than that which causes it and why immediately on its creation the lightening becomes visible to the eye while thunder requires time to travel. How the various circles of water form around the spot which has been struck by a stone and why a bird sustains itself in the air. These questions and other strange phenomena engaged my thought throughout my life.

Drawing is based upon perspective, which is nothing else than a thorough knowledge of the function of the eye.

The lover is moved by the thing loved, as the sense is by that which perceives, and it unites with it and they become one and the same thing... when the lover is united with the beloved it finds rest there; when the burden is laid down there it finds rest.

A bird maintains itself in the air by imperceptible balancing, when near to the mountains or lofty ocean crags; it does this by means of the curves of the winds which as they strike against these projections, being forced to preserve their first impetus bend their straight course towards the sky with divers revolutions, at the beginning of which the birds come to a stop with their wings open, receiving underneath themselves the continual buffetings of the reflex courses of the winds.

Motion is created by the destruction of balance.