Weight is caused by one element being situated in another; and it moves by the shortest line towards its centre, not by its own choice, not because the centre draws it to itself, but because the other intervening element cannot withstand it.

The eye transmits its own image through the air to all the objects which face it, and also receives them on its own surface, whence the "sensus communis" takes them and considers them.

The eye - which sees all objects reversed - retains the images for some time.

The worst evil which can befall the artist is that his work should appear good in his own eyes.

A good painter has two main objects to paint, man and the intention of his soul.

No human investigation can be called real science if it cannot be demonstrated mathematically.

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.