34 
POPULAR SCIENCE REVIEW. 
tlie proposition in some valuable statistics too long for quota- 
tion, showing that the yearly value of London smoke, now lost, 
amounts to 2,125,000/. 
Another important point to which attention has recently been 
drawn is the very partial and local character of a fog. Passengers 
by the Great Northern Railway, for instance, can easily observe its 
great prevalence in the valley below the ridge of clay hills termed 
the ‘ Hog’s Back,’ which form the northern wall of the basin of 
the Thames. On arriving at Finsbury Park, the line of demar- 
cation is often distinct and wall-like. Here, no doubt, the geo- 
graphical position, and the impervious nature of the strata, 
will account for the peculiarity. A similar case was noticed by 
Mr. White, the Secretary of the Royal Institute of Architects, 
on the 7th of December, in a letter addressed to the Times . He 
inquires whether the parks may not, in some degree, be respon- 
sible for the fogs which periodically obscure parts of London. 
The fog of December 2nd last is known to have prevailed prin- 
cipally in the northern, north-western, and western districts ; at 
the termini of the North-Western and Midland Railways great 
inconvenience was felt. Now, on the afternoon of that day, at 
about half-past four, Mr. White passed through the Regent’s Park, 
and there observed over a vast space, the circumference of which 
is three miles, a dense mass of bluish vapour rising, apparently, 
from the grass. In the midst of this vapour a feeling of damp 
cold was experienced, with a tendency to cough, while his beard 
and moustache were covered with globules of water. Objects 
at a few yards’ distance could not be distinguished ; both in the 
Euston Road and at Gloucester Gate the enclosure- walls of dif- 
ferent houses streamed with moisture. At a later hour, at 11.30 
p.m., he was in Portland Place, where foot-passengers clung to 
the area railing as the only means available for directing their 
steps. Arrived, however, at Oxford Circus, the fog was less dense ; 
at the eastern end of Oxford Street comparatively little existed. 
He traversed the slums of Soho, Co vent Garden, and the Strand, 
without any difficulty, and the City was free from fog. 4 1 beg,’ 
he says, * scientific men who are interested in this matter to visit 
the Regent’s Park any day this winter between 4 and 5 p.m. 
I have been told that the drainage there is of an obsolete cha- 
racter, and from my experience of this and last year, when 
London has been visited with fog, the cloud has seemed to me 
to be thicker in Portland Place than in Oxford Street, or even in 
the Strand.’ 
The publication of the above letter gave rise to a lively 
correspondence, two independent correspondents confirming 
Mr. White’s facts ; and a third, Dr. G. V. Poore, adding the 
following comment : — 
‘ If your correspondents will refer to Jordan’s Geological 
