Those who are enamored of practice without science are like a pilot who goes into a ship without rudder or compass and never has any certainty of where he is going. Practice should always be based upon a sound knowledge of theory.

Just as iron rusts from disuse, and stagnant water putrefies, or when cold turns to ice, so our intellect wastes unless it is kept in use.

The greatest geniuses sometimes accomplish more when they work less.

M a k e yo u r s e l f a m a s t e r o f perspective, then acquire perfect knowledge of the proportions of men and other animals.

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

He who truly knows has no occasion to shout.

Whoever in debate quotes authority uses not intellect, but memory.

The motive power is the cause of all life.

The five senses are the ministers of the soul.

The eye is the window of the human body through which it feels its way and enjoys the beauty of the world.