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14
METEOROLOGICAL OBSERVATIONS.
I am indebted to Dr. H. Spencer Jones, Astronomer Royal,
for the following meteorological data for the year ended December,
1938.
The mean temperature was 51.3°, which is 1.8° higher than
the average for 75 years, 1841-1915. The highest temperature in
the shade was 84.0° registered on August 6th. Temperatures
exceeding 80° were recorded on 8 days. The lowest temperature
was 20.4° on December 20th. Temperatures of freezing point or
below were recorded on 23 days, 11 of which were in December and
only 1 in January.
The mean daily horizontal movement of the air was 298 miles,
which is 13 miles above the average for 50 years, 1867-1916. The
greatest daily movement was 656 miles on January 15th ; the
least daily movement was 131 miles on March 23rd. The greatest
motion in one hour was 37 miles, on January 15th and the greatest
pressure was 33.2 lbs. to the square foot, on November 23rd.
The duration of bright sunshine recorded was 1341.8 hours or
30.0 per cent, of the possible total.
There were 59 entirely sunless days, 15 being in January
and 13 in December. The total rainfall was 19.51 inches, which is
4.72 inches less than the average for the 75 years 1841-1915. The
whole amount occurring in the five months February to June
was only 3.13 inches and there is no previous instance of such a
small rainfall in a corresponding period at Greenwich. April was
the driest month with 0.10 inch ; November was the wettest month
with 3.09 inches. Measurable rain fell on 160 days. There were
two periods of absolute drought exceeding 20 days, namely March
2nd to 23rd and April 4th to 24th.
With regard to pollution of the air by solids in suspension,
exceptionally bad days were February 6th and October 25th.
At one time during October 25th the amount reached 5.8 milligrams
per cubic metre, that is approximately 9.5 lbs. in the volume of
air contained in a cube with one hundred yards edge.
The mean amount of solid matter in suspension during the
period covered by " Summer Time " increased from 0.48 milligrams
per cubic metre in 1937 to 0.54 milligrams in 1938. It appears
that conditions have not improved.
With regard to gaseous pollution, the average amount over
the whole period was found to be 0.046 parts of sulphur dioxide
per million parts of air, which is rather less than the average for
the previous twelve months. During the twenty-four hours ending
noon October 26th, the amount was 0.531 parts per million, which
is the greatest amount yet recorded.