Nature is constrained by the cause of her laws which dwell inborn in her. Variant: Nature is constrained by the order of her own law which lives and works within her.

The variety of colour in objects cannot be discerned at a great distance, excepting in those parts which are directly lighted up by the solar rays.

Human subtlety will never devise an invention more beautiful, more simple or more direct than does nature because in her inventions nothing is lacking, and nothing is superfluous.

It vexes me greatly that having to earn my living has forced me to interrupt the work and to attend to small matters.

I am still hopeful. A falcon, Time. But the coincidence is probably accidental.

When you look at a wall spotted with stains...you may discover a resemblance to various landscapes, beautiful with mountains, rivers, rocks, trees. Or again, you may see battles and figures in action, or strange faces and costumes, and an endless variety of objects which you could reduce to complete and well-drawn figures.

A day will come in which men will look upon an animal's murder the same way they look today upon a man's murder.