Chapter CXXI

As a means of practising this perspective of the variation and loss or diminution of the proper essence of colours, take at distances, a hundred braccia apart, objects standing in the landscape, such as trees, houses, men, and places, and in front of the first tree fix a piece of glass so that it is quite steady, and then let your eye rest upon it and trace out a tree upon the glass above the outline of the tree; and afterwards remove the glass so far to one side that the actual tree seems almost to touch the one that you have drawn. Then colour your drawing in such a way that the two are alike in colour and form, and that if you close one eye both seem painted on the glass and the same distance away. Then proceed in the same way with a second and a third tree, at distances of a hundred braccia from each other. And these will always serve as your standards and teachers when you are at work on pictures where they can be applied, and they will cause the work to be successful in its distance. But I find it is a rule that the second is reduced to four-fifths the size of the first when it is twenty braccia distant from it.

_Leonardo._