A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
In a Street, running East and West, the Sun being in the Meridian, and the Walls opposed to the Sun, raised so high, as to screen the Bodies below, from the Solar Rays, the Air at the same time being not too much illumined; is found a very advantagious place, for the disposition of Figures; and they are there, always seen to receive an uncommon Grace, and Relievo: For the two sides of the Face, in this case, participate of the obscurity of the two opposite Walls; and the Nose, with the rest of the Face, looking to the West, will be illumined; so that the Eye which is here supposed to be placed at the end of the Street, will at the same time see the sides of the Face, shadowed by the Walls, and the Front part enlighten'd. To this it must be added, that the Shadows will not appear harsh, and stiff in their extremes; but will fall off, and lose themselves insensibly; a circumstance which contributes very considerably to the Gracefulness of the Figure. Now the reason of this tenderness of the Shadows, is owing to the Light, diffused in the Air, which striking on the Pavement of the Street, is reflected on the shadowed sides of the Face, and tinges them with a faint Lightness. Further, the Light reflected from the Tops of the Houses, and received in at the end of the Street, will illumine the Face, to the very Source, as it were of the Shadows arising under it, weakening them by little and little, till they come to terminate on the tip of the Chin, in a Shadow almost insensible on every side. For Example, suppose this Light were A E, [Tab. 2. Fig. 2.] the Line F E of the Light, you see, illumines that part of the Face under the Nose, the Line C F only illumining that under the Lip, and the Line A H that underneath the Chin; so that the Nose must needs be more strongly illumined, than any other part, since it receives Light from all the Points A B C D E.