OcTOLER 30. 1902 | 
sword-grass that cuts likea knife, known as ‘‘oom soof.” The 
steamer could cut its own way through the latter in the presence 
Fic. 1.—Steamer towing out a block of sudd. 
of acurrent, as it would break up and float down stream. In 
the absence of current it does not float away, and obstructs the 
Fic. 2.—Block of sudd let go in open water. 
steamer by fouling the paddle-wheel. Another source of 
obstruction is a very light kind of duckweed which covers some | 
of the small open pools. 
THE TREATMENT OF SMOKE: A SANITARY 
PARALLEL)! 
Introductory. 
es accepting the suggestion that I should take as my subject 
some aspect of the fog question, I have allowed the im- 
portance of the question to override the many considerations 
which I could adduce in opposition thereto. I propose to con- 
sider what demands sanitary reformers may fairly make upon | 
1 Abstract of a lecture to the Sanitary Congress at Manchester by 
Dr. W. N. Shaw, F.R.S. 
NO. 1722, VOL. 66] 
NATURE 
667 
practical men of science and others in regard to the miti- 
gation of the evil effects of fog in towns, and incidentally to 
point out what demands in this connec- 
tion, desirable in themselves, must be 
regarded as beyond the scope even of 
scientific ambition. 
For the sake of clearness, what I 
have to say is cast in the form of a paral- 
lel or analogy. The smoke in fog is the 
element of the problem to which special 
attention is directed, and the smoke is 
regarded as a species of domestic or in- 
dustrial refuse which has to be removed 
somehow or other. The removal of 
smoke is a problem not dissimilar in its 
fundamental character from that of the 
removal of sewage, and in what I have 
to say I keep in view the analogy that 
exists between the elements of these two 
problems. I choose the problem of the 
removal of sewage for this purpose, 
because it is a problem in which sanitary 
reformers have achieved gradual but con- 
spicuous success during the nineteenth 
century, and even within the memory of 
the present generation, to the great 
advantage of the whole community. 
In all matters concerning the disposal 
of refuse, we progress by slow degrees 
from an individualist to a _ socialist 
point of view. Occasional illustrations of reckless indulgence 
of the extreme individualist view as regards the disposal of 
other forms of refuse might be quoted, 
and at this day it is no great exaggera- 
tion to say that we all act with similar 
recklessness with regard to our smoke ; 
we throw it into the atmosphere and 
leave to beneficent chance the question 
whether or not it injures our neigh- 
bours. 
In large towns, we have travelled very 
far in the path of development from the 
original instinct as regards the problem of 
the disposal of sewage-polluted water, 
but there has been no corresponding 
progress in the disposal of smoke-polluted 
air. In London, at a cost to the com- 
munity of 211,000/. a year, or 1°38d. in 
the pound on rateable value, nearly a 
million tons of sewage are removed day 
by day for about 600,000 houses—about 
a ton and a half on the average for each 
house. In the same period, viz. each 
day, in winter, each house throws into 
the atmosphere on the average perhaps 
ten tons of smoke-laden air, or a total 
quantity of five million tons of smoke- 
laden air for the inhabited houses of 
London per day, or possibly seven 
millions of tons per day if we include 
factories. The actual weight of solid 
soot which gives colour and body to the 
smoke is a very uncertain quantity ;. it 
may in the worst cases amount to nearly 
3 per cent. of the coal consumed, and the houses of London 
probably get rid of 300 tons of solid refuse every day by 
throwing it up the chimney. It is mixed with much larger 
quantities of other more or less injurious products of the com- 
bustion of coal, complete or incomplete, but it is with the soot, 
which alone darkens and defiles, that I am primarily concerned. 
The Initial Stages of the two Problems. 
The difference of our attitude towards these two problems is 
very conspicuous, yet physically speaking the whole difference 
between the problem of the removal of sewage and that of the re- 
moval of smoke on similar lines lies in the distinction that sewage 
naturally goes downwards, whereas, in the first instance, smoke 
goes upwards. If the smoke of our fires had been in the habit 
| of falling downwards and finding a lower level instead of rising 
' to a higher level and making its way up the chimney, we should 
