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39
DRAINAGE.
are porous in the least procurable degree; such as
consequently will be least apt to imbibe and retain
in their interstices any considerable impregnation
from the foetid fluids running over them at intervals;
such, too, as will be least likely to permit soakage
into the surrounding soil: thirdly, by reducing the
size of drains and sewers to the lowest dimensions
compatible with a full performance of their uses, to
diminish to the utmost the extent of their interior
evaporating surface, and of those large chambers
which they now offer for the evolution, retention, and
diffusion of gases.
To the application of these principles (together
with a sufficient and appropriate distribution of
water) far more than to chemical agents, or to the
invention of mechanical traps, I believe that you
must look for rendering inodorous the vicinity of
your numerous gully-holes. I content myself with
stating them to you, as a practical deduction from
physical laws, without venturing to offer any opinion
on the degree in which they are applicable within
your jurisdiction, or on the manner in which they
should be applied. For although, as principles, they
have their foundation in physics, and although their
importance to sanitary improvement is beyond measure
great, all details relating to their application
lie out of my province, and belong to a class of subjects
in which your Surveyor's opinion will, of course,
be infinitely more useful to you than mine.
D 2