of the organ of sight, we cannot see distant objects so distinctly as nearer ones, yet aërial perspective is grounded strictly on the important fact that all mediums called transparent are in some degree dim.
869.
The atmosphere is thus always, more or less, semi-transparent. This quality is remarkable in southern climates, even when the barometer is high, the weather dry, and the sky cloudless, for a very pronounced gradation is observable between objects but little removed from each other.
870.
The appearance on a large scale is known to every one; the painter, however, sees or believes he sees, the gradation in the slightest varieties of distance. He exemplifies it practically by making a distinction, for instance, in the features of a face according to their relative position