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57
Atmospheric
pollution.
In addition to the maintenance of deposit gauges in six open spaces in the county,
undertaken by the Council as a contributing body of the Research on Atmospheric
Pollution, conducted by the department of Scientific and Industrial Research,
observations of visibility have been continued from the fleche at County Hall. An
examination of the relation of the horizontal range of visibility to the fog shade
indicated on the Owens' recording filter shows that the mean monthly distance of
the farthest visible objects falls off rapidly until a mean monthly fog shade of 1
(=0.02 m.g. suspended carbon per cubic metre) is reached when the limit of visibility
is about a mile. Greater amounts of soot have a lessened effect on visibility, and it
is clear that some such point must be reached since the possible range becomes very
small and there are no degrees of invisibility. A real but less marked correlation
was observed between the total deposit collected in a gauge near County Hall
and the sulphate in that deposit and the visibility in the direction of the gauge.