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converted by oxidation and other changes into carbon dioxide and marsh gas which
were identified and determined in the air drawn from depths of 1 foot 6 inches and
3 feet below the surface. In this process of mineralisation the greater part of the
organic nitrogen is retained by the mass. Several species of plants grew freely on
the surface of the heap and much of it was disposed of as a top dressing for grass in
London parks.
Observations of visibility and actinicity.
Of the environmental conditions affecting health and well-being there are none
to which greater importance can be attached than those which are comprehended
in the atmospheric complex. Little understood in their mode of action they are a
common circumstance operative over considerable areas and affecting vast numbers
of persons.
Of recent years attention has more particularly been paid to atmospheric pollutions
and especially as they affect the air of cities. Coal smoke and the other products
of combustion from the domestic and the factory chimney, dust and grit emitted into
the air from industrial processes and from the grind and attrition inseparable from
the activities of a great city have each received a large measure of attention and
become the subject of systematic record.
Some years ago the Council sanctioned the keeping of observations asked for
by the Advisory Committee on Atmospheric Pollution and a considerable amount of
work in this connection has been done and the results forwarded to the Advisory
Committee. Occasion was taken to expand some of these observations in directions
more immediately bearing upon health and the results are now presented for the
first time.
The Flèche of the County Hall afforded an excellent view-point from which to
measure horizontal visibility as it was affected by the varying seasonal and other
conditions of the London atmosphere. Record was also made of the actinic power
of the light, a property which to an increasing degree is recognised as having a direct
and very important bearing on health.
At 10 a.m. and at noon, G.M.T., these observations have been systematically
recorded on each week-day since September, 1923.
One fact comes out clearly as a result of the three years' records when the data
are distributed and compared according to season.
The summer months are the period of greatest horizontal visibility at noon in
London, the mean range being 5.6 miles for the months of June, July, and August,
as compared with a range of 2.5 and 2.6 miles respectively for the spring and autumn
months. The winter mean is only 0.9 of a mile. Generally speaking, low visibility
is associated with low actinicity of the light. Measured by actinometer and expressed
as the number of seconds taken to turn a standard paper to a given tint, the mean
figures are summer, 17 seconds, and spring and autumn, 36 seconds and 38 seconds
respectively and winter, 63 seconds.
If the individual months are taken, comparison shows the same close correspondence—see
Table II. No correlation appears to be established when comparison
is made with the amounts of deposits collected in the rain gauges which are a measure
of the impurities washed out of the atmosphere by rainfall. This method of measuring
atmospheric impurities is open to many disturbing factors and cannot be relied on
as an index of suspended impurities in the atmosphere at times other than those
immediately preceding rainfall. The automatic filter records made by Dr. Owen’s
instrument (a means of separating the finer particles yielding varying shades of
blackness to the paper through which the air is filtered) on the other hand, show a
very close correlation both to the data of visibility and of actinicity. The summer
months yield much the lowest figure of blackening; the averages being for summer
0.6, spring and autumn, 1.0 and 1.1 respectively, and winter, 1.4.