A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
'Tis no difficult matter, for a Painter to represent a Figure forty Fathoms high, standing erect on its Feet, in a space of only half that height; since neither in this, nor in any other Case need he trouble himself about the Wall, on which he Paints; and especially when his Work is to be viewed from a Window, or some other determinate Place; because the Eye, is not to concern it self with the Evenness or Curvity, of the Surface on which the Painting is made; but only with the Force and Conduct of the Things represented in the Painting: Twill be convenient, however, to chuse a Surface that may be a regular Curve, as for instance, F R G; [Tab. 2. Fig. 6.] since in that Case, your Work will be free from the Interruption of Angles.