304? Betrospedive Criticisnu 



London Fogs. — Fogs happen^every where, caused by the upper region 

 of the atmosphere being colder than the lower, by which the ascent of 

 aqueous vapour is checked, and kept arrested near the surface of the 

 earth. But fogs are more dense about London, and probably all other 

 great cities, than elsewhere : the reason is, because the vast quantity of 

 fidiginous matter floating over such places mingles with the vapour, and 

 renders the whole so thick that a noonday darkness is sometimes produced, 

 rendering candles and gas-lights necessary for the transaction of the ordi- 

 nary business of the shops and public offices. Such circumstances happen 

 frequently during winter; but on some occasions (as about 2 P.M. on 

 the 27th Dec, 1831) this foggy darkness was truly awful. This extra- 

 ordinary appearance is, however, caused by a very ordinary accident, viz. 

 a change of wind ; and which may be accounted for as follows : — The 

 west wind carries the smoke of the city to the eastward in a long train, 

 extending to the distance of twenty or thirty miles ; as may be seen in a 

 clear day, by any person on an eminence five or six miles from the city, 

 and looking across the direction of the wind ; say from Harrow on the 

 Hill, for instance. In this case, suppose the wind to change suddenly to 

 the east, the great body of smoke will be brought back in an accumulated 

 mass, and as this repasses the city, augmented by the clouds of smoke from 

 every fire therein, it causes the murky darkness alluded to. This effect 

 of the smoke's being thrown back on its source may be easily conceived ; 

 indeed, it may be seen under favourable circumstances, first reverted, and 

 gradually accumulating, till it is dispersed on the opposite side; but 

 wherever the accumulation is, in its progress backward, there will be an 

 unusual degree of darkness. It is to be observed, that the cause of fogs is 

 also the cause of the smoke floating near the earth; of course, where there 

 is much of the latter the former is doubly dense. Besides fogs, we have 

 also mists or haze, usually accompanying east winds, especially in the 

 spring months. In the counties to the westward of the metropolis this 

 mist is called London smoke ; but, as it is seen to the eastward as well as 

 westward of the city at the same time, the appellation is improper. It is 

 observed mostly under a cloudless sun, in consequence of its reflecting the 

 blue rays of light, or perhaps the azure tinge of the sky ; hence it is also 

 called a blue mist. So imposing is this in real landscape, that the painter 

 embodies it on the canvass. Aerial perspective cannot well be given 

 without an imitation of this haze, and which constitutes one of the greatest 

 excellencies of pictorial execution. Very differently is this appearance 

 estimated by many orchardists : they call it a blight, and consequently 

 deprecate the east wind. It is perfectly true that tender vegetation suffers 

 under the withering effect of easterly winds, and the hot sun at that season 

 brings forth myriads of aphides and other insects, from ova previously laid 

 on the trees ; but that they are brought by the east wind is as ridiculous 

 as untrue. The most rational idea we can form of this hazy appearance 

 is, its being caused by the constitutional coldness of the east wind, which, 

 checking the ascent of vapour raised by the sun, carries it horizontally 

 along the lowest stratum of the air, hence its visibility. A lurid gloom 

 is sometimes produced by clouds of snow; when the water floating in the 

 air becomes frozen into spicula, and, congregating into flakes, contrary 

 currents of wind wheel them into irregular masses, which obstruct the 

 light from the sky, so as to wrap every object immediately below in deep 

 yellow light. This circumstance almost always precedes, and is a certain 

 sign Of, a fall of snow. — /. M. Jan. 14. 1832. 



