FOG.
LONDON clay and the Essex marshes are two factors which help to keep the soil and air of East London cold, and so to condense the vapour in the air till it turns to fog. But as fog requires particles of dust to be a nucleus for each vaporation, the smoke and soot which in the still weather that always accompanies fog cannot be wafted away provide such a fine "vehicle" for the water to con- dense on as to give London the very first place among fog- ridden towns, though the centre of a good Leeds fog is, if anything, rather stronger in bouquet and fine keeping quality.
We certainly have not in the least improved away any portion of our London fogs. Consequently it may be guessed that we do not know everything that is to be known about the story of the mist. While no one can give a proper explanation of the remarkable way in which a fog helps to fill a pond, raising the water inches in a night, it can hardly be expected that the movements, and, if we may say so, the shapes, of fogs should be fully accounted for either. Fog will come across bright sea like a solid, upright wall. Occasionally it does so in London too, though, as the city is mainly cut up by streets, and we are walking in each at the bottom of a kind of crack, the march of the fog-wall is seldom noticed before it is over the observer. Last winter such an advance of fog was seen in Hyde Park with great distinctness. It was a sunny afternoon, with a gentle south-easterly breeze, when the wind changed to the east, temperature fell, and a solid black wall some thousand feet high was seen coming up and advancing along the Serpen- tine as if some one had hung up a black blanket, and was sweeping it forward, held up at each corner by invisible hands like the veil in some Hebrew prophet's vision. There was ice on the lake, though not strong enough to skate on, and the bottom folds of the fog-blanket were seen curling up and roll- ing like a puff of dark smoke. It travelled fast, and soon overtook the onlookers with its partial eclipse. This " steep- ness " accounts ' for the local character of fogs. It may be black in the Strand and sunny in Cavendish Square.
Fog and mist, if they hang all day, are a great curse in country districts. They seldom lie as long as in the towns, or rival that which hung over London from November, 1879, till the following February. But they bring a plague of cold and darkness even in the open fields, and an' very destructive to health and life. The last six weeks of the great London fog of 1879 saw a rise in the death-rate of from seventeen hundred in a week to nearly two thousat,d five hundred. In the country fogs blight the crops, in addition to lowering the vitality of the people. The wetting clouds called sea- fogs, which come in from the ocean at a height of from two hundred to four hundred feet, are very destruc- tive to corn when in bloom, and also to apple blossom. The only vegetation which never seems to su 'Ter from constant mists is the heather, mosses, and rush-grass of the moors and fells. These plants seem to enjoy playing the role of per. petual condensers. But trees, which act as alembics, and distil water from fog till the ground below them is "all in a float," as Gilbert White says, suffer from overmuch use for this purpose. Constant mists keep their boughs and bark perpetually wet, for the unfortunate tree cannot stop con- densing when it has had enough. Mosses and lichens grow thick upon it, and in course of time it decays before its prime. On the hills the fogs generally appear to be dry. Sometimes they are, as when Cobbett watched them on Hanger Hill, a kind of "dry clouds." But they are usually supersaturated, so that the least object drains the water from them. They are not like the common morning mists of summer, in which the sun's rays soon evaporate the water which has formed round the dust particles in the air, and so leave them dry and invisible again.
Any one who studies the ways of fogs on the high hills will notice that these vapours follow certain courses, keeping to regular hollows or heights, and gathering thickly in some places and thinly in others. They have their channels in the air and on the ground surface, just as water has in a river- bed, with a quick stream here, a deep pool there, and in other places thin flats. Where winter fogs lie heavy and long there is generally a cold clay beneath the surface, however genial that may appear to the eye. Thus in the district round Bracknell and parts of Ascot; where late autumn fogs are very persistent, it will probably be found that under the sandy gravel which produces the heather and fern there is cold clay. Invery heavy fogs and mists in the Thames Valley below London the stress and trouble caused by the fogs are evident even by day. Repeated explosions from the railway lines show the precautions taken to prevent accident; yet the very men who lay those signals, which have to be placed on the rails, are sometimes killed. From the river come the moaning of the sirens, the shrieking of the whistles, the roar of gongs, the booming of fog-horns, and occasionally a signal gun, showing that all is confusion, darkness, and con- straint upon the crowded river.
Fogs must be flat upon the top. It is not often that this is seen, but it is so. Looking down on a mist, the top is often as level as a lake. Some years ago a long frost-fog, following snow, filled the Vale of White Horse to a height varying very little between 700 ft. and 650 ft. above the level of the sea. This coincided with the Ridgeway along the crest of the downs. On the top the eye saw over miles of brilliant snow, lighted up by the low winter sun. Below all was cloud and darkness.
Nothing is so bewildering as fog. Only animals which find their way by scent can get about in it with any certainty. Birds are entirely bewildered by it. Tame pigeons remain all day motionless and half asleep, huddled up either in, or just outside, their pigeon-houses. Chickens remain motionless for hours in heavy fogs. No bird sings or utters a call in such weather, perhaps because it fears to betray its whereabouts to an enemy. The writer saw an extraordinary instance of a person lost in a fog last winter. It was a weeping frost-fog, which caused the water to form first into icicles on the trees and then to fall to the ground and scatter into splashes of ice. In a field next to the road was a blind man wandering about, feeling his way with a stick. This man was in the habit of coming up every day from a little town two miles off carrying notes and parcels, and had scarcely ever lost his way before. Asked why he had gone astray (for he is quite blind, and weather might be supposed to make no difference), he said that in a fog the ground sounded quite different. In the woods such weather makes shooting quite impossible, partly on account of the danger, partly from the reluctance of pheasants to rise. When flushed there is no saying where they will go. They lose their sense of direction, and scatter over the country. Even when not disturbed, they wander on foot great dis- tances in thick weather. It should be added that seagulls do not seem to fear the mists, possibly because there is no such danger to sea birds as that of being lost within reasonable distance of the coast. At the same time, they are much less disposed to wander far from the rocks in fogs. Hence their great value to sailors up the English Channel, both as guides to fishermen returning to their village and as signallers to the great ships creeping and feeling their way up Channel when they are borne by currents too near the rooks. Seagulls
are the sirens of the fog, but warning the seamen from peril, not alluring them.
To ships at sea a fog is a greater peril than a storm. By day it is a steady menace, by night a blind terror. A long modern steamer may enter a wall of fog so sharply that to a person standing near the stern the front portion of the ship may be invisible before the fog reaches the stern. Nothing but a dead atop, obligatory on all vessels, could deerease the peril of the fog at sea. As no rule of the kind could be en- forced, the ships creep on at a slow yet dangerous speed, with no other signal but the steady moaning of the foghorn and the blast of the steam whistles, like some lost monster of the ocean bowling across the deep. But the fog, which baffles sight, plays tricks with sound. It is never safe to guess where another ship is passing by reckoning its place by sound. The reason why sea-fog by day is almost more dangerous than it is by night is that at night, even though light travels only a few dozen yards, there is just the chance that a ship may make out the woolly glare before she is cut down, or cute another down. By day there is not even that chance of warning. There is some- thing almost pathetic in the helplessness, and as it were the fatalism, of the fishing crews whose tiny boats lie out through a fog in the North Sea, on the line of the great steamers. Each fishing boat has its wretched lantern, and its tiny jangling bell, which the man of the watch keeps moving until the great ship either passes by, or perhaps passes over, the crazy little craft. Round Spitsbergen and the adjacent seas fog is the normal condition for many months in the year. The contact of the Arctic current flowing north of Newfoundland raises the thickest fog-banks known where it meets or impinges on the warm air from the Gulf Stream and the South. A bold proposal was once considered, not for getting rid of the Newfoundland fogs, but for changing the climate of Canada, by blocking up the Straits of Belleisle, and so barring out the whole of the Arctic current from the Gulf of the St. Lawrence, and leaving this gulf to be filled by the warmer currents entering by the Northumberland Straits south of Newfoundland. It was believed that the cold of the Canadian winter was largely caused by the mass of icy water which collects in the Gulf of the St. Lawrence, and that the substitution of warmer water would give it a climate of a far milder type.
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