a b. [Footnote 8: Compare No. 177.]
If the size of the illuminating body is larger than that of the illuminated body an intersection of shadow will occur, beyond which the shadows will run off in two opposite directions as if they were caused by two separate lights.
On the relative intensity of derived shadows (175-179).
175.
ON PAINTING.
The derived shadow is stronger in proportion as it is nearer to its place of origin.
176.
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