IX. The Practice of Painting: 518.

5: For the same reason a window thus constructed would be convenient for an illuminator or a miniature painter.

: M. RAVAISSON in his edition of the Paris MS. A remarks on this passage: "La figure porte les lettres f et g, auxquelles rien ne renvoie dans l'explication; par consequent, cette explication est incomplete. La figure semblerait, d'ailleurs, se rapporter a l'effet de la reflexion par un miroir concave." So far as I can see the text is not imperfect, nor is the sense obscure. It is hardly necessary to observe that c d here indicate the wall of the room opposite to the window e and the semicircle described by f g stands for the arch of the sky; this occurs in various diagrams, for example under 511. A similar semicircle, Pl III, No. 2 (and compare No. 149) is expressly called 'orizonte' in writing.