A London Fog is not like any other fog you may have encountered.  
It it is an entity in itself.  

NOTES ON LONDON FOG
A City of Shadows Exclusive

From Dickens’ Dictionary of London, 1883

 

FOGS are, no doubt, not peculiar to London. Even Paris itself can occasionally turn out very respectable work in this way, and the American visitor to England will probably think, in passing the banks of Newfoundland, that he had very little to learn on the subject of fog.  But what Mr. Guppy called “a London particular” and what is more usually known to the natives as a “pea-souper”, will very speedily dispel any hallucination of this sort.  As the east wind brings up the exhalations of the Essex and Kentish marshes, and as the damp-laden winter air prevents the dispersion of the partly consumed carbon from hundreds of thousands of chimneys, the strangest atmospheric compound known to science fills the valley of the Thames. At such times almost all the senses have their share of trouble. Not only does a strange and worse than Cimmerian darkness hide familiar landmarks from the sights, but the taste and sense of smell are offended by the unhallowed compound of flavours, and all things become greasy and clammy to the touch.  During the continuance of a real London fog – which may be black, gray, or more probably orange-coloured – the happiest man is he who stays at home.  But if business – there is no such things as out of doors pleasure during the continuance of a London fog – should compel a sally into the streets, one caution should be carefully observed.  Mr. Catlin, well known for his connection with the Indian Tribes of North America, once promulgated into print a theory, that a royal road to long life was, sleeping or waking, to keep the mouth as much as possible closed.  This advice, whatever its value may be generally should always be followed when a London fog has to be encountered. Nothing could be more deleterious to the lungs an the air-passages then the wholesale inhalation of the foul air and floating carbon, which, combined, form a London fog.  In this connection it may be taken as an axiom that the nose is Nature’s respirator. The extraordinary effect which the fogs of the winter of 1879-1880 had upon the health of Londoners will be long remembered. It is almost unnecessary to add that the dangers of the streets, great at all times, are immeasurably increased in foggy weather; and that the advantages of being able to dive into that unnatural darkness after a successful robbery, are thoroughly appreciated by the predatory classes.

From The London Perambulator, James Bone, 1925

The voices in the air of unseen busmen and carmen and draymen take on a rounder heartiness excelling their own best efforts when they are visible men, and the policemen loom up in the fog with added grandeur. They require it all, for there is a spirit of misrule abroad; newsboys play tricks and cry strange news, and strait-laced citizens find themselves in public houses, strange companionships are formed, judges and prisoners on bail lose their way and are reported missing at the courts, people go to the wrong theatres, accidents occur and the ambulance gets lost. Cats come out into busy streets and sit on the pavement as if it was night. Anachronisms like torches and links appear. Only twenty years ago a man going home about midnight in a fog saw a glare of torches and a body of men passed with King Edward walking in the middle. The torches were carried by footmen and policemen; then came the king, heavily wrapped up, with two of his gentlemen; then more policemen; then some stragglers of the night, attracted by curiosity or by the chance of a safe guide to Buckingham Palace. The procession came so silently out of the fog and vanished into it again that the spectator later in the night was not sure that he had not imagined it. But it was King Edward, who had been dining with a Court lady in Portman Square, and, finding it impossible to go by carriage in the fog, had decided to summon torches and a guard and walk just as a Stuart king would have done.

 

From H. G. Wells, Love and Mr Lewisham, 1900

 

Wonderfully varied were those seven-and-sixty nights, as he came to remember in after life. There were nights of damp and drizzle, and then thick fogs, beautiful, isolating grey-white veils, turning every yard of pavement into a private room. Grand indeed were those fogs, things to rejoice at mightily. Since then it was no longer a thing for public scorn when two young people hurried along arm in arm, and one could do a thousand impudent, significant things with varying pressure and the fondling of a little hand (a hand in a greatly mended glove of cheap kid). Then indeed one seemed to be nearer that elusive something that threaded it all together. And the dangers of the street corners, the horses looming up suddenly out of the dark, the carters with lanterns on their horses' heads, the street lamps, blurred smoky orange at one 5 nearest, and vanishing at twenty yards into dim haze, seemed to accentuate the infinite need of protection on the part of a delicate young lady who had already traversed three winters of fogs thornily alone. Moreover, one could come right down the quiet street where she lived, with a delightful sense of enterprise. The fogs passed all too soon into a hard frost, into nights of starlight and presently moonlight, when the lamps looked hard, flashing like rows of yellow gems, and their reflections and the glare of the shop windows were sharp and frosty, and even the stars hard and bright, snapping noiselessly (if one may say so) instead of twinkling. A jacket trimmed with imitation Astrachan replaced Ethel's lighter coat, and a round cap of Astrachan her hat, and her eyes shone hard and bright, and her forehead was broad and white beneath it. It was exhilarating, but one got home too soon, and so the way from Chelsea to Clapham was lengthened, first into a loop of side streets, and then when the first pulverulent snows told that Christmas was at hand, into a new loop down King's Road, and once even through the Brompton Road and Sloane Street, where the shops were full of decorations and entertaining things.

From Compton Mackenzie, Sinister Street, 1913

 

The cries of a London twilight used to oppress him. From the darkening streets and from the twinkling houses inexplicable sounds floated about the air. They had the sadness of church-bells, and like church-bells they could not be located exactly. Michael thought that London was the most melancholy city in the world. Even at Christmas-time, behind all the gaiety and gold of a main road lay the trackless streets that were lit, it seemed, merely by pin-points of gas, so far apart were the lamp-posts, such a small sad circle of pavement did they illuminate. The rest was shadows and glooms and whispers. Even in the jollity of the pantomime and comfortable smell of well-dressed people the thought of the journey home through the rainy evening brooded upon the gayest scene. The going home was sad indeed, as in the farthest corner of the jolting omnibus they jogged through the darkness. The painted board of places and fares used to depress Michael. He could not bear to think of the possibilities opened up by the unknown names beyond Piccadilly Circus. Once in a list of fares he read the word Whitechapel and shivered at the thought that an omnibus could from White chapel pass the corner of Carlington Road. The very omnibus had actually come from the place murders were done. Murderers might at this moment be travelling in his company. Michael looked askance at the six nodding travellers who sat opposite, at the fumes of their breath, at their hands clasped round the handles of their umbrellas. There, for all he knew, sat jack the Ripper.

From A Wanderer In London, E.V. Lucus, 1924

I want to say one other word about romantic London before we really enter Park Lane.  Beneath one of her mists or light fogs London can become the most mysteri­ous and beautiful city in the world.  I know of nothing more bewitchingly lovely than the Serpentine on a still misty evening-when it is an unruffled lake of dim pearl­grey liquid, such stuff as sleep is made of.  St. James's Park at dusk on a winter's afternoon, seen from the suspension bridge, with all the lights of the Government offices reflected in its water, and the turrets and gables of Whitehall Court against the sky, has less mystery but more romance.  It might be the lake before an enchanted castle. And while speaking of evening effects I must not forget the steam which escapes in fairy clouds from the huge chimney off Davies Street, just behind the Bond Street Tube Station.  On the evening of a clear day this vapour can be the most exquisite violet and purple, trans­figuring Oxford Street.

 

To artists the fog is London's best friend.  Not the black fog, but the other.  For there are two distinct London fogs-the fog that chokes and blinds, and the fog that shrouds.  The fog that enters into every corner of the house and coats all the metal work with a dark slime, and sets us coughing and rubbing our eyes-for that there is nothing to say.  It brings with it too much dirt, too much unhealthiness, for any kind of welcome to be possible.  "Hell is a city much like London," I quoted to myself in one of the worst of such fogs, as I groped by the railings of the Park in the Bayswater Road. The traffic, which I could not see, was rumbling past, and every now and then a man, close by but invisible, would call out a word of warning, or some one would ask in startled tones where he was.  The hellishness of it consisted in being of life and yet not in it-a stranger in a muffled land.  It is had enough for ordinary way­farers in such a fog as that; but one has only to imagine what it is to be in charge of a vehicle, to see how much worse one's lot might be.

But the other fog-the fog that veils but does not obliterate, the fog that softens but does not soil, the fog whose beautifying properties Whistler may he said to have discovered-that can be a delight and a joy.  Seen through this gentle mist London becomes a city of romance.  All that is ugly and hard in her architecture, all that is dingy and repellent in her colour, disappears.

"Poor buildings," wrote Whistler, who watched their transformation so often from his Chelsea home, "lose themselves in the dim sky, and the tall chimneys become campanili, and the warehouses are palaces in the night, and the whole city hangs in the heavens."

 

I have said that it was Dickens who discovered the London of eccentricity, London as the abode of the odd and the quaint, and Stevenson who discovered London as a home of romance.  It was Whistler who discovered London as a city of fugitive, mysterious beauty.  For decades the London fog had been a theme for vituperation and sarcasm: it needed this sensitive American-Parisian to show us that what to the commonplace man was a foe and a matter for rage, to the artist was a friend. Every one knows about it now.

 

Fogs have never been quite the same to me since I was shown a huge chimney on the south side of the Thames, and was told that it belonged to the furnaces that supply London offices with electric light; and that whenever the weather seems to suggest a fog, a man is sent to the top of this chimney to look down the river and give notice of the first signs of the enemy rolling up.  Then, as his news is communicated, the furnaces are re-stoked, and extra pressure is obtained that the coming darkness may be fought and the work of counting-houses not inter­rupted.  All sentinels, all men on the look-out belong to romance; and from his great height this man peering over the river shipping and the myriad roofs for a thick­ening of the horizon has touched even a black London fog with romance for me.  I think of his straining eyes, his call of warning, those roaring fires. . .