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85
egular intervals during the 21 hours. The air drawn through leaves a
deposit on the white paper. The degree of intensity of the mark, corresponding
to the amount of suspended impurities, is then compared with a
scale of standard tints. This instrument, which was designed by Dr. J. S.
Owens, and known as the " automatic air filter," has been so devised
that the scale of tints correspond to pounds of suspended impurities per
million cubic yards of air.
(3) Estimation of sulphur gas as SO2. The method of investigation
was described in the reports for 1931-32. It need only be said that this
is the first occasion on which sulphur gas readings have been exhibited in
graphic form. Last year the results were given in statistical tables. The
scheme of the chart opposite is the work of Messrs. Sutton and Davies,
the Council's Inspectors, who have given a great deal of time to the
Council's investigations into atmospheric pollution. This particular chart
has received the commendation of Dr. Owens, Superintendent of Observations
on behalf of the Department of Scientific and Industrial Research,
and may possibly be adopted at other stations where sulphur gas is
measured.
The chart indicates the amount of sulphur gas correlated with visibility,
wind-direction and rainfall during 1933, and the amount of sulphurous
mpurities (calculated as sulphur dioxide) in parts per million in the
atmosphere compared with the " visibility." The code used for " visibility
" readings is that issued by the Meteorological Office, and is as
follows:—
0. Dense fog Objects not visible at 55 yards.
1. Thick fog „ „ 220 „
2. Fog „ „ 550 „
3. Moderate fog „ „ 1,100 „
4. Mist or haze „ „ 11/4 miles.
5. Poor visibility „ „ 21/2 „
6. Moderate visibility „ „ 61/4 „
7. Good visibility „ „ 121/2 „
8. Very good visibility „ „ 31 „
9. Excellent visibility Beyond 31 miles.
The general wind direction and rainfall during the period of observation
are shown. It is interesting to note that the amount of pollution follows
the general " line " of the visibility. The periods of observations are those
of 24 hours in each week, and are generally made between 10 a.m.
Thursday and 10 a.m. Friday.
(9489) G