"It seems not impossible to reduce to the simplicity of rule or principle, what may have appeared difficult in this branch of art to young students, and may have been too often pursued at random by others. All forms in nature, both animate and inanimate, partake of the round form more than of any other shape; and when lighted, whether by the sun or flame, or by apertures admitting light, must have two relative extremes of light and shadow, two balancing tints, the illuminated and the reflected, divided by a middle tint or the aerial. The effect of illumination by flame or aperture, differs from that of the sun in this respect; the sun illuminates with parallel rays, which fall over all parts of the enlightened side of the subject, while the light of a flame or an aperture only strikes directly on the nearest point of the object, producing an effect which more or less resembles the illumination of the sun in proportion to the distance and dimensions of the object. "Let us then suppose a ball to be the object on which the light falls, in a direction of forty-five degrees or the diagonal of a square, and at a right angle from the ball to the place where you stand. One half of the ball will appear illuminated, and the other dark. This state of the two hemispheres constitutes the two masses of light and shadow. In the centre of the mass of light falls the focus of the illumination in the ball; between the centre of the illumination and the circle of the ball, where the illumination, reaches its extremity, lies what may be called the transparent tint; and between it and the dark side of the ball lies the serial or middle tint. The point of darkness, the extreme of shade, is diametrically opposite to the focus of illumination, between which and the aerial tint lies the tint of reflection. If the ball rests on a plain, it will throw a shadow equal in length to one diameter and a quarter of the ball. That shadow will be darker than the shade on the ball, and the darkest part will be where the plain and ball come in contact with each other. "This simple experiment, whether performed in the open sun-shine, or with artificial illumination, will lead you to the true principles of light and shade over all objects in nature, whether mountains, clouds, rocks, trees, single figures, or groups of figures. It would therefore be of great use, when you are going to give light and shade to any object, first to make the experiment of the ball, and in giving that light and shade, follow the lessons with which it will furnish you.