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14
METEOROLOGICAL OBSERVATIONS.
I am indebted to Dr. H. Spencer Jones, Astronomer Royal,
for the following extracts from his Report to the Board of Visitors
and which covers the period May 1st, 1936 to April 30th, 1937.
The registration of atmospheric pressure, temperature of the
air and of evaporation, the direction, pressure and velocity of the
wind, the amount of rainfall, of sunshine and of cloudiness at
night has been maintained continuously. Estimates of visibility
have been made by eye at definite hours.
The measurement, by a continuously recording photographic
apparatus, of the air-earth current discharged at a metallic point
30 feet above ground level has been maintained throughout the year.
Interpretation of the records is complicated by the presence of
parasitic currents partly of thermo-electric origin.
Regular records for measurement of the amount of solid matter
polluting the air have been continued using an Owens automatic
filter. Tabulation of the results shows that there has been little
change in the average amount since the last report. In the summer
months there was an apparent reduction of about 10 per cent;
in the ensuing winter the improvement was not more than 5 per
cent. The reduction in solid pollution on Saturdays appears to
average about 5 per cent., while a further reduction of about the
same amount occurs on Sundays.
The gaseous pollution of the atmosphere by sulphur dioxide
has been measured daily. The days of worst pollution were November
25th and 28th, 1936 when the amount was estimated to be
respectively, 0.262 and 0.222 parts per million. The average
pollution during the year ended April 30th, 1937, was 0.056 parts
per million by volume. This is an increase of about 25 per cent.
on the amount for the corresponding period twelve months earlier.
The following meteorological data relate to the period January
to December 1937.
The mean temperature was 50.5°, which is 1.0° higher than the
average of 75 years 1841-1915. The highest temperature in the
shade was 91.9° registered on August 6th. Temperatures exceeding
80° were recorded on 22 days. The lowest temperature was 23.7°
on March 10th. Temperatures of freezing point or below were
recorded on 48 days, of which 13 were in March. The mean daily
horizontal movement of the air was 255 miles, which is 30 miles
below the average for 50 years 1867-1916. The greatest daily
movement was 559 miles recorded on January 6th and 28th;
the least daily movement was 81 miles, on December 25th. The
greatest motion in one hour, 30 miles, and the greatest pressure
reached, 15.7 lbs. to the square foot, were recorded on January 18th.