Chap. CCCXX.—Of Objects seen in a Fog.
Objects seen through a fog will appear larger than they are in reality, because the aerial perspective does not agree with the linear, viz. the colour does not agree with the magnitude of the object[1]; such a fog being similar to the thickness of air interposed between the eye and the horizon in fine weather. But in this case the fog is near the eye, and though the object be also near, it makes it appear as if it were as far off as the horizon; where a great tower would appear no bigger than a man placed near the eye.
- ↑ To our obtaining a correct idea of the magnitude and distance of any object seen from afar, it is necessary that we consider how much of distinctness an object loses at a distance (from the mere interposition of the air), as well as what it loses in size; and these two considerations must unite before we can decidedly pronounce as to its distance or magnitude. This calculation, as to distinctness, must be made upon the idea that the air is clear, as, if by any accident it is otherwise, we shall (knowing the proportion in which clear air dims a prospect) be led to conclude this farther off than it is, and, to justify that conclusion, shall suppose its real magnitude correspondent with the distance, at which from its degree of distinctness it appears to be. In the circumstance remarked in the text there is, however, a great deception; the fact is, that the colour and the minute parts of the object are lost in the fog, while the size of it is not diminished in proportion; and the eye being accustomed to see objects diminished in size at a great distance, supposes this to be farther off than it is, and consequently imagines it larger.