form, to represent a principal group; but it is only available for the master who can see in it what he has the power of producing.
857.
In order to make the first idea intelligible to the beginner, (for it is difficult to consider it abstractedly even in a polygon,) we may take a cube, the three sides of which that are seen represent the light, the middle tint, and the shadow in distinct order.
858.
To proceed again to the chiaro-scuro of a more complicated figure, we might select the example of an open book, which presents a greater diversity.
859.
We find the antique statues of the best time treated very much with reference to these effects. The parts intended to receive the light are wrought with