Page:A Treatise on Painting.djvu/284

 and the eye. The vapours mixing with the air in the lower regions near the earth, render it thick, and apt to reflect the sun’s rays on all sides, while the air above remains dark; and because light (that is, white) and darkness (that is, black), mixed together, compose the azure that becomes the colour of the sky, which is lighter or darker in proportion as the air is more or less mixed with damp vapours.   shadows of bodies produced by the redness of the setting sun, will always be blueish. This is accounted for by the eleventh proposition, 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 Rh