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substitution therefor of ventilating shafts of sufficient
calibre (not less than 6")—one shaft being always taken,
if practicable, from the highest point of the Sewer, which,
if a stunted or dead end, should be tacked on to a
neighbouring Sewer, to allow of free circulation of air.
7. The upward movement of air in shafts is increased by gas,
which, when burning, acts as an exhaust; so that no
difficulty should be placed in the way of the London
County Council in their endeavour to relieve the pressure
in the Sewers (over which they have jurisdiction), by
erecting ventilating extraction shafts, which are in the
form of large lamps placed upon street refuges.
The proper ventilation of sewers is an important matter,
and the middle course seems to be the best, i e., to avoid,
on the one hand, the view that no ventilation at the street
level is necessary, and, on the other, the view that sewer
gas is perfectly innocuous, and can, therefore, be allowed to
escape at any and every position in the public thoroughfares,
irrespective of the width of such thoroughfares.
Properly laid sewers, efficiently flushed, are a sine qua
r.on.