PROLEGOMENA AND GENERAL INTRODUCTION TO THE BOOK ON PAINTING

which is in itself infinitely divisible, and I prove it thus:—[Footnote 7: See Pl. XXXI, No. 1; the two upper sketches.] Let a g be a continuous surface and let d be the light which illuminates it; I say—by the 4th [proposition] which says that that side of an illuminated body is most highly lighted which is nearest to the source of light—that therefore g must be darker than c in proportion as the line d g is longer than the line d c, and consequently that these gradations of light—or rather of shadow, are not 4 only, but may be conceived of as infinite, because c d is a continuous surface and every continuous surface is infinitely divisible; hence the varieties in the length of lines extending between the light and the illuminated object are infinite, and the proportion of the light will