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26
why so little is evolved into the air, is because it is fixed
in combination with the iron of the clay that is always
suspended in the water. This is an interesting illustration
of the beneficial uses of the clay that I pointed out in
the first report in which I referred to this subject.
The offensiveness of the river was first mitigated
by the cool northerly winds and the powerful springtides
of the end of June. The temperature of the air
and of the water fell several degrees. But still no
complete relief was experienced until the rainfall of
the first week in July. During the week ending July
10th, the measured rainfall Avas 1-37 inches. But the
freshet had regained power enough to flush the London
part of the river, and to purify it on the 6 th or 7th, when
scarcely .50 inch had fallen. With the freshet there
came down large quantities of that excellent deodoriser,
clay, in a state of minute division. Ever since the water
has presented a clear yellow color, from this cause.
This appearance is always an index of the salubrity of
the river. It is desirable to know more accurately the
rainfall in the upland districts which feed the river. Still
it appears that less than an inch of rain, even in the
hottest weather, is sufficient for the temporary purification
of the river.
These facts point conclusively to the measures
necessary for the preservation of the salubrity of the
Thames in London; and reveal the fallacy of the idea