28 
POPULAR SCIENCE REVIEW. 
in tlie surrounding country it was a foggy day, but there the 
fog was grey, whereas in London it was, at about the boundary 
line, dark yellow, and a little within it, brown, and then 
browner, until at the heart of the city — which they call 
St. Mary Axe — it was rusty black. From any point of the 
high ridge of land northward, it might have been discerned 
that the loftiest buildings made an occasional struggle to get 
their heads above the foggy sea, and especially that the great 
dome of St. Paul’s seemed to die hard ; but this was not 
perceivable in the streets at their feet, where the whole 
metropolis was a heap of vapour charged with muffled sound 
of wheels and enfolding a gigantic catarrh.’ * 
Scientific opinion, however, is far from unanimous as to the 
exact nature of the phenomenon. A recent correspondent of 
the Times newspaper, Dr. Alfred Carpenter, who led off the 
latest crisis alluded to above, boldly jumped at the conclusion 
that fog is simply powdered carbon diffused in the air, and 
issuing as such from non- smoke- consuming fire-places. This 
view is, however, demonstrably erroneous. It is easy to pass a 
large quantity of very foggy atmosphere through a small fluid 
or cotton -wool filter by means of what is termed by chemists an 
‘ aspirator ; ’ weighing the intercepting material before and after 
experiment. The increase of weight will be found infinitesi- 
mally small ; the microscope, moreover, shows at those times 
hardly any increase, and in some cases a decrease in the quantity 
of finely divided carbon, which is always, to a certain extent, 
present in the air of large towns. It can be noticed by every 
person that the days when those literal betes noires of the house- 
keeper, ‘ the blacks,’ fall on papers, books, and furniture, are not 
foggy, but the reverse, being usually dry, bright, and windy. 
And yet common sense and experience indicate some form of 
connexion between coal, smoke, and fog, of the ‘ London par- 
ticular ’ variety. Its practical limitation to our coal-burning 
metropolis, and to some other large towns, such as York, where 
the same conditions prevail, is a strong argument in this direc- 
tion. The writer’s personal observation supplies another fact of 
the same bearing. When he was a student in Paris in the year 
1856, wood was still the fuel burnt in the close stoves of that city ; 
and the fogs which often delayed him on his journey to early 
morning visit at 7 a.m. in the old Hotel Dieu, though dense, were 
almost white, and like country mist. Napoleon III. was, however, 
encouraging the use of coal, and hearths for burning it were 
rapidly replacing the old poele, or the pair of dogs for supporting 
the burning log. Before his year of study ended, the character 
of the fog had materially changed ; no doubt owing to the 
altered fuel, and several well-marked specimens of the London 
* Dickens, Our Mutual Friend , iii. 1. 
