The vivacity and brightness of colors in a landscape will never bear any comparison with a landscape in nature when it is illumined by the sun, unless the painting is placed in such a position that it will receive the same light from the sun as does the landscape.

A single and distinct luminous body causes stronger relief in the objects than a diffused light; as may be seen by comparing one side of a landscape illuminated by the sun, and one overshadowed by clouds, and illuminated only by the diffused light of the atmosphere.

A heightened sense of the observation of nature is one of the chief delights that have come to me through trying to paint. I accumulated in those years so fine a surplus in the Book of Observance that I have been drawing confidently upon it ever since.

The air moves like a river and carries the clouds with it; just as running water carries all the things that float upon it.

The beginnings and ends of shadow lie between the light and darkness and may be infinitely diminished and infinitely increased. Shadow is the means by which bodies display their form. The forms of bodies could not be understood in detail but for shadow.

Although human ingenuity may devise various inventions which, by the help of various instruments, answer to one and the same purpose, yet will it never discover any inventions more beautiful, more simple or more practical than those of nature, because in her inventions there is nothing lacking and nothing superfluous; and she makes use of no counterpoise when she constructs the limbs of animals in such a way as to correspond to the motion of their bodies, but she puts into them the soul of the body.