As fog has now been abolished both on sea and land, and as few of the
present generation have even seen one, it may not be out of place to
give a few lines on the subject of fogs in general, and the London fogs
in particular, which through local peculiarities differed from all
others. A fog was simply watery vapor rising from the marshy surface of
the land or from the sea, or condensed into a cloud from the saturated
atmosphere. In my day, fogs were a great danger at sea, for people then
travelled by means of steamships that sailed upon the surface of the
ocean.
London at the end of the 19th century consumed vast quantities of a
soft bituminous coal for the purpose of heating rooms and of preparing
food. In the morning and during the day, clouds of black smoke were
poured forth from thousands of chimneys. When a mass of white vapor
arose in the night these clouds of smoke fell upon the fog, pressing it
down, filtering slowly through it, and adding to its density. The sun
would have absorbed the fog but for the layer of smoke that lay thick
above the vapor and prevented the rays reaching it. Once this condition
of things prevailed, nothing could clear London but a breeze of wind
from any direction. London frequently had a seven days' fog, and
sometimes a seven days' calm, but these two conditions never coincided
until the last year of the last century. The coincidence, as everyone
knows, meant death--death so wholesale that no war the earth has ever
seen left such slaughter behind it. To understand the situation, one
has only to imagine the fog as taking the place of the ashes at
Pompeii, and the coal-smoke as being the lava that covered it. The
result to the inhabitants in both cases was exactly the same.