214 
LONDON FOGS. 
^'^ Fogs/' says Mr. Main, " are more dense about London, and probably all other 
great cities, tban elsewhere, because the vast quantity of fuliginous matter floating 
over such places mingles with the vapour, and renders the whole so thick that a 
noon-day darkness is sometimes produced, rendering candles and gas-lights neces- 
sary for the transaction of the ordinary business of the shops and public offices. 
Such circumstances happen frequently during winter ; but on some occasions (as 
about two o'clock p.m. on the 27th December, 1831) this foggy darkness was truly 
awful. This extraordinary appearance is, however, caused by a very ordinary 
accident, viz. a change of winds, 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 per- 
son on an eminence five or six miles from the city, and looking across the directions 
of the wind, say at 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 being thrown back on its source may be easily conceived ; indeed it 
may be seen under favourable circumstances, first reverted, and gradually accumu- 
lating, 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 so 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 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 cloud- 
less 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 canvas. Aerial perspective cannot 
well be given without an imitation of this haze, and which constitutes one of the 
greatest excellences 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 wither- 
ing 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 smw."'—Mag. Nat. Hist. 
Vol. F.jf9.304. 
