A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
'Tis an universal Fault, and which Painters every day run into in Painting the Fronts of Churches and Chappels, that after finishing some History-Piece, with the Landskip, Buildings, &c. they go on to paint other Pieces, over, and by the side of the first, still changing the Perspective Point; so that the same Front shall be painted with several different Points of View; than which nothing can be more absurd; the Point of View in any Painting representing the Eye of a Spectator. If you ask then, how the Life of any Saint divided into several Histories, may be painted on the same Front? I answer, that you must place your first Plan, with its perspective Point, at such a height as may be the most suitable to those who are to view it below; representing your principal History in large, upon this first Plan, and still diminishing the Figures and Buildings for the rest of your Subject, according to the different Situations they are placed in. In the rest of the Front towards the Top, you may paint Landskips, with Trees, proportionate to the Figures, or Angels, if the History require it, or Birds, or barely the Heavens with Clouds and the like Incidents. Without this Conduct, 'twill be much better for you to let these sorts of Paintings alone; for your whole Work will be false, and contrary to the Rules of Opticks.