It’s something you can’t quite grasp but you can see and feel it — sometimes in your bones.
You don’t need a graveyard or a lonely cawing crow to feel a little bit creepy in a blanket of fog.
Fog pushes the big noisy world out to the edge and leaves a cocoon of silence with just the tiniest sliver of delicious dread — what’s out there?
If you’re a glass-of-wine-at-midnight-and-log fire sort of person, fog is also rather comforting.
Lifting a curtain to peep out of the window to find you are possibly the only person left on earth does wonders for the imagination.
Mary Shelley did not dream up the story of Frankenstein one sunny afternoon on a crowded beach in the south of France.
She came up with idea of a man returned to life through science to become a monster — during an evening of ghost stories with the mad poets Lord Byron and Percy Shelley on the shores of Lake Geneva in 1816. It was June, so it was probably a clear night — but in our imaginations she was surrounded by clinging, thick grey fog.
The subsequent movies made of her creation certainly delivered fog.
Fog creates its own universe of mystery.
When I was young I lived in Somerset, England — a remorselessly flat place where the land had been reclaimed from the sea centuries ago.
When winter fog rolled in at night from the sea my father would fire up his old Rover 95 and take us out for drive to watch for the ‘‘will o’ the wisps’’ which he was certain appeared every time there was fog.
Hey remember — this was before the exciting internet and live streams on Facebook, okay?
We nudged carefully down lanes over the boggy open flatlands criss-crossed by ‘‘reens’’ — small murky irrigation channels overhung with willow branches.
The world was a grey blanket punctured by the occasional window light of a house or a pub. Nobody else was mad enough to go for a leisurely drive through a sea fog. We never once saw the mythical ‘‘will o’ the wisp’’ — it was always a magical spirit just far enough away to be invisible.
But my father, a chemist and a dreamer, was convinced they were out there.
By my teens I was convinced he was spinning tales to amuse himself, or chasing a Don Quixote dream.
Years later when my father was long dead I returned to Somerset to show my Australian family where I had spent my youth.
Naturally, when a sea fog rolled in, we went for a drive.
My three-year-old son was in the back seat and I spun him a yarn about the will o’ the wisp who only appeared when the fog arrived.
I told him to keep his eyes peeled as we drove slowly down the murky lanes alongside the reens.
Suddenly my mouth dropped and I jammed on the brakes.
In the distance I saw something flicker. It was a floating green blob about the size of a golf ball.
Cripes, I thought — the old man was right. Strange things really are out here.
I shivered, but my young son just watched quietly.
It was nothing special — just a little fairy going home in the fog.
The scientific explanation offered for a will o’ the wisp or jack ‘o lantern is that it is a flame-like phosphorescence caused by gases from decaying plants in marshy areas.
But as with many things that fog brings — the mystery is so much more exciting than the reality.
John Lewis is chief of staff at The News.