"The first requisite of painting is that the bodies which it represents should appear in relief, and that the scenes which surround them with effects of distance should seem to enter into the plane in which the picture is produced by means of the three parts of perspective, namely the diminution in the distinctness of the form of bodies, the diminution in their size, and the diminution in their colour. Of these three divisions of perspective the first has its origin in the eye, the two others are derived from the atmosphere that is interposed between the eye and the objects which the eye beholds."