HOW SHADOWS FADE AWAY AT LONG DISTANCES. Shadows fade and are lost at long distances because the larger quantity of illuminated air which lies between the eye and the object seen tints the shadow with its own colour. 177. _a b_ will be darker than _c d_ in proportion as _c d_ is broader than _a b_. [Footnote: In the original MS. the word _lume_ (light) is written at the apex of the pyramid.] 178. It can be proved why the shadow _o p c h_ is darker in proportion as it is nearer to the line _p h_ and is lighter in proportion as it is nearer to the line _o c_. Let the light _a b_, be a window, and let the dark wall in which this window is, be _b s_, that is, one of the sides of the wall. Then we may say that the line _p h_ is darker than any other part of the space _o p c h_, because this line faces the whole surface in shadow of [Footnote: In the original the diagram is placed between lines 27 and 28.] the wall _b s_. The line _o c_ is lighter than the other part of this space _o p c h_, because this line faces the luminous space _a b_. Where the shadow is larger, or smaller, or equal the body which casts it. [First of the character of divided lights. [Footnote 14: _lumi divisi_. The text here breaks off abruptly.] OF THE COMPOUND SHADOW _F, R, C, H_ CAUSED BY A SINGLE LIGHT. The shadow _f r c h_ is under such conditions as that where it is farthest from its inner side it loses depth in proportion. To prove this: Let _d a_, be the light and _f n_ the solid body, and let _a e_ be one of the side walls of the window that is _d a_. Then I say--according to the 2nd [proposition]: that the surface of any body is affected by the tone of the objects surrounding it,--that the side _r c_, which faces the dark wall _a e_ must participate of its darkness and, in the same way that the outer surface which faces the light _d a_ participates of the light; thus we get the outlines of the extremes on each side of the centre included between them.] This is divided into four parts. The first the extremes, which include the compound shadow, secondly the compound shadow between these extremes. 179. THE ACTION OF THE LIGHT AS FROM ITS CENTRE. If it were the whole of the light that caused the shadows beyond the bodies placed in front of it, it would follow that any body much smaller than the light would cast a pyramidal shadow; but experience not showing this, it must be the centre of the light that produces this effect. [Footnote: The diagram belonging to this passage is between lines 4 and 5 in the original. Comp. the reproduction Pl. IV, No. 4. The text and drawing of this chapter have already been published with tolerable accuracy. See M. JORDAN: "_Das Malerbuch des Leonardo da Vinci_". Leipzig 1873, P. 90.] PROOF.