Thus, when the eye is quite uncultivated, it sees that a man is a man,and a face is a face, but has no idea what shadows or lights fall upon the form or features. Cultivate it to some degree of artistic power, and it will then see shadows distinctly, but only the most vigorous of them. Cultivate it still farther, and it will see light within light, and shadow within shadow, and will continually refuse to rest in what it had already discovered, that it may pursue what is more removed and more subtle, until at last comes to give its chief attention and display its chief power on gradations which to an untrained faculty are partly matters of indifference, and partly imperceptible.