Any thing white will appear whiter, by being opposed to a dark ground; and, on the contrary, darker upon a light ground. This we learn from observing snow as it falls; while it is descending it appears darker against the sky, than when we see it against an open window, which (owing to the darkness of the inside of the house) makes it appear very white. Observe also, that snow appears to fall very quick and in a great quantity when near the eye; but when at some distance, it seems to come down slowly, and in a smaller quantity [47].
Chap. CCXIII.—Of Reverberation.
Reverberations are produced by all bodies of a bright nature, that have a smooth and tolerably hard surface, which, repelling the light it receives, makes it rebound like a foot-ball against the first object opposed to it.
Chap. CCXIV.—Where there cannot be any Reverberation of Light.
The surfaces of hard bodies are surrounded by various qualities of light and shadow. The lights are of two sorts; one is called original, the other derivative. The original light is that which comes from the sun, or the brightness of fire, or else from the air. The derivative is a reflected light. But to return to our definition, I say, there can be no reflexion on that side which is turned towards any dark body; such as roofs, either high or low, shrubs, grass, wood, either dry or green; because, though every individual part of those objects be turned towards the original light, and struck by it; yet the quantity of shadow which every one of these parts produces upon the others, is so great, that, upon the whole, the light, not forming a compact mass, loses its effect, so that those objects cannot reflect any light upon the opposite bodies.
Chap. CCXV.—In what Part the Reflexes have more or less Brightness.
The reflected lights will be more or less apparent or bright, in proportion as they are seen against a darker or fainter ground; because if the ground be darker than the reflex, then this reflex will appear stronger on account of the great difference of colour. But, on the contrary, if this reflexion has behind it a ground lighter than itself, it will appear dark, in comparison to the brightness which is close to it, and therefore it will be hardly perceptible [48].