In Painting, 'tis much more difficult, and requires a great deal more Thought and Reflection, to give the Shadows to a Figure, than to Design its Contours; this is easily proved, for the out Lines of any Object, may be Designed through a Plane Glass, situate between the Eye, and the thing to be imitated; but this Invention is useless, with regard to the Shadows; on account of their Diminution, and the insensibility of their Extremes, which for the most part are confusedly mingled with one another: as I have already shewn in my Treatise of Lights and Shadows.