An artist is obliged forever to hold a balance in his hand, by which he must determine the value of different qualities; that, when _some_ fault must be committed, he may choose the least. Those painters who have best understood the art of producing a good effect have adopted one principle that seems perfectly conformable to reason; that a part may be sacrificed for the good of the whole. Thus, whether the masses consist of light or shadow, it is necessary that they should be compact and of a pleasing shape: to this end some parts may be made darker and some lighter, and reflections stronger than nature would warrant. Paul Veronese took great liberties of this kind. It is said, that being once asked why certain figures were painted in shade, as no cause was seen in the picture itself, he turned off the inquiry by answering, "_Una nuevola che passa_"--a cloud is passing, which has overshadowed them. But I cannot give a better instance of this practice than a picture which I have of Rubens; it is a representation of a Moonlight. Rubens has not only diffused more light over the picture than is in nature, but has bestowed on it those warm glowing colours by which his works are so much distinguished. It is so unlike what any other painters have given us of Moonlight, that it might be easily mistaken, if he had not likewise added stars, for a fainter setting sun. Rubens thought the eye ought to be satisfied in this case, above all other considerations; he might, indeed, have made it more natural, but it would have been at the expense of what he thought of much greater consequence--the harmony proceeding from the contrast and variety of colours.