Chap. CCLXXXV.—The Cause of the Diminution of Colours.
The natural colour of any visible object will be diminished in proportion to the density of any other substance which interposes between that object and the eye.
Chap. CCLXXXVI.—Of the Diminution of Colours and Objects.
Let the colours vanish in proportion as the objects diminish in size, according to the distance.
Chap. CCLXXXVII.—Of the Variety observable in Colours, according to their Distance, or Proximity.
The local colour of such objects as are darker than the air, will appear less dark as they are more remote; and, on the contrary, objects lighter than the air will lose their brightness in proportion to their distance from the eye. In general, all objects that are darker or lighter than the air, are discoloured by distance, which changes their quality, so that the lighter appears darker, and the darker lighter.
Chap. CCLXXXVIII.—At what Distance Colours are entirely lost.
Local colours are entirely lost at a greater or less distance, according as the eye and the object are more or less elevated from the earth. This is proved by the seventh proposition [71], which says, the air is more or less pure, as it is near to, or remote from the earth. If the eye then, and the object are near the earth, the thickness of the air which interposes, will in a great measure confuse the colour of that object to the eye. But if the eye and the object are placed high above the earth, the air will disturb the natural colour of that object very little. In short, the various gradations of colour depend not only on the various distances, in which they may be lost; but also on the variety of lights, which change according to the different hours of the day, and the thickness or purity of the air, through which the colour of the object is conveyed to the eye.