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12
65 or 3 percent, less. A similar diminution of moisture
is observed at St. Mary's Hospital, Paddington; and
what is still more remarkable at the Board of Health,
Whitehall, which is very near the river. During this
week there was no rain-fall, and scarcely any wind to
disturb the comparison. What then became of the
vapour that was lost between the Thames and Hackney
and Paddington? And if the vapour did not reach
those places, may it not be presumed that the Thames
impurities also were lost on the way?
There is another physical test. During the week
j ust selected for examination, from the foulness of the
Thames being then at its height, there was, as already
observed, nearly a calm state of the atmosphere. In
such a condition the gases of the Thames could only
be distributed over the metropolis, under the operation
of that law of gaseous diffusion, by virtue of which one
gas or aeriform body penetrates or mixes with another
gas when simply placed in contact. Now taking the
Thames as a centre from which the presumed diseaseproducing
gases radiate all over London, it is obvious
that these gases must be diluted by the common
atmosphere which receives them, in at least the ratio
of the squares of the distances from that centre.
I leave it to the upholders of the Thames-theory to
determine what infinitesimal quantity of miasma it is
that reaches Shoreditch, Islington, or St. Pancras, after
this dilution, and exposure to all the decomposing forces
in operation in the atmosphere.