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21
of the river in its London course are subject to great
disturbing causes, which are likely to increase year by
year. In the beginning of January 1857, I laid
down a scheme of observation of the waters of the
Thames, the results of which clearly illustrate the conditions
upon which the preservation of the purity of
the river depends. The waters of the Thames are affected
by many circumstances, namely, seasons, temperature of
the air, temperature of the water itself, locality, period
of the day, period of the tide, spring and neap tides, wind,
agitation, rainfall, and the reception of foreign matters.
A correct knowledge of the influence of these circumstances
could only be obtained by continuous and
methodical observations. Specimens were therefore
collected alongside the Dreadnought, which lies nearly
in mid-stream, and at a spot where the changes to
which the water is exposed, are well marked. Every
week two specimens taken, one at high, the other at low
water, were examined chemically and microscopically
by Dr. Odling and myself, and the analyses tabulated
in connection with the varying phases of the conditions
enumerated. I found that in January, the quantity of
dissolved organic and inorganic matter was very small
both at high and low water. It was found that as the
summer advanced, the quantity of organic and inorganic
matter increased greatly, both in high and low water,
and that it fell again as the winter advanced. Was this
apparent increase of impurity during the summer, entirely
owing to the greater proportion of sewage? No