It is therefore necessary, “that those parts of round bodies which are seen directly opposite to the spectator, should have the light entire;” and that the extremities turn, in losing themselves insensibly and confusedly, without precipitating the light all on the sudden into the shadow, or the shadow into {275.} the light. But the passage of one into the other, must be common and imperceptible, that is, by degrees of lights into shadows, and of shadows into lights. And it is in conformity to these principles, that you ought to treat a whole group of figures, though it be composed of several parts, in the same {280.} manner as you would do a single head: “or if the wideness of the space, or largeness of the composition, requires, that you should have two groups or three, [*†280.] (which should be the most,) let the lights and shadows be so discreetly managed, [*†283.] that light bodies may have a sufficient mass or breadth of shadow to sustain them, and that dark bodies may {285.} have a sudden light behind to detach them from the ground. [*†286.] “As in a convex mirror, the collected rays strike stronger and brighter in the middle than upon the natural object, and the vivacity of the colours is increased in the parts full in your sight; [*†290.] while the goings off are more and more broken and faint as they approach to the extremities, in the same manner {290.} bodies are to be raised and rounded.” Thus the painter and the sculptor are to work with one and the same intention, and with one and the same conduct. For what the sculptor strikes off, and makes round with his tool; the painter performs with his pencil, casting behind that which he makes less visible, by the diminution and breaking {295.} of his colours: “That which is foremost and nearest to the eye, must be so distinctly expressed, as to be sharp, or almost cutting to the sight. Thus shall the colours be disposed upon a plane, which from a proper place and distance will seem so natural {300.} and round, as to make the figures appear so many statues. [Sidenote: XXXII. Of dark bodies on light grounds.] “Solid bodies subject to the touch, are not to be {305.} painted transparent; and even when such bodies are placed upon transparent grounds, as upon clouds, waters, air, and the like vacuities, they must be preserved opaque,[142] that their solidity be not destroyed among those light, aërial, transparent species; and must therefore be expressed sharper and rougher than what is next to them, more distinct by a firm light and shadow, and with more solid and {310.} substantial colours; that, on the contrary, the smoother and more transparent may be thrown off to a farther distance.” [Sidenote: XXXIII. That there must not be two equal lights in a picture.]