30 
POPULAR SCIENCE REVIEW. 
sulphurous acid. The utmost that could he attained by smoke- 
preventing grates would he the prevention of the discharge of 
carbon in powder. For the rest, the conditions would remain 
the same ; the fogs would be cleaner, and that is all.’ 
It is thus obvious that other modes of accounting for fog 
must be sought for besides the crude and simple hypothesis of 
suspended carbon. This view was well developed in a lecture 
by Captain Douglas Gralton, recently delivered at the meeting 
of the Balloon Society at Westminster Aquarium. He stated 
that from the surrounding of the sea the climate of England was 
more moist than many other climates, and had, therefore, a 
greater tendency to fogginess. In London fog resulted not alone 
from this cause and from the Thames, but from the exhalations 
of open spaces, where the rain had sunk into the soil. The 
canopy of compacted smoke from the 5,000,000 tons of coals 
annually used in the Metropolis prevented the evaporation of 
water, and caused the irritating effects of London fog. There 
were also the emanations from street- sweepings, manure-heaps, 
and the breath of millions of inhabitants, resulting, it was com- 
puted, in nineteen grains of sulphuric acid in every cubic yard 
of London air. Balloon experiments by Mr. Griaisher and 
others had proved that the fogs were not usually of high alti- 
tude, and that the sun was sometimes shining on high towers 
when all below was enveloped in mist. 75 per cent of light 
was thus intercepted, to the great detriment of animal and 
vegetable life, accounting, to some extent, for the comparative 
feebleness of London children. By way of reducing the dele- 
terious influences, open spaces should be well under- drained, 
and, if practicable, more spaces or boulevards laid out to admit 
freer circulation of air. While smoke from factories could be 
checked, every private house was in winter a manufactory of 
smoke and soot. The use of smokeless coal and of smoke-con- 
suming appliances would mitigate the evil ; but it seemed to 
him that private houses might eventually be supplied with heat 
from some central source by means of electricity. 
The best contribution, however, that we possess to the natural 
history of Fog is hardly so well known to the general public as 
it should be. This is mainly due to the fact that it is short and 
unpretending, and also to its being enshrined, and, to a certain 
degree, concealed, in the Proceedings of the Royal Society. 
On October 29, 1878, Prof. Frankland forwarded to his 
brother fellows a brief memoir occupying exactly three pages, 
but containing within this limited space very condensed and 
substantial matter. It is entitled, ‘ On Dry Fog/ and 
begins by stating the well-known fact that the foggy atmo- 
sphere, especially near large towns, is not always saturated with 
moisture. For instance, on the 17th of that month, at 3.30 p.m., 
