Chap. CCLVIII.—Why the Shadows of Bodies upon a white Wall are blueish towards Evening.
The shadows of bodies produced by the redness of the setting sun, will always be blueish. This is accounted for by the eleventh proposition[1], which says, that the superficies of any opake body participates of the colour of the object from which it receives the light; therefore the white wall being de-
prived entirely of colour, is tinged by the colour of those bodies from which it receives the light, which in this case are the sun and the sky. But because the sun is red towards the evening, and the sky is blue, the shadow on the wall not being enlightened by the sun, receives only the reflexion of the sky, and therefore will appear blue; and the rest of the wall, receiving light immediately from the sun, will participate of its red colour.
- ↑ See the note on the chapter next but one preceding. The proposition in the text occurs in chap. ccxlvii. of the present work.