tantly employed, and
an arrangement of fans or wings, mounted either upon the fronts of the
boats or attached to the bottoms of the little trucks which run on rails
along the edges of the canal of the larger sewers. These fans descend
into the canal and sweep all obstructions before them,--the sand from
the street pavements overhead constituting a large portion of this
obstructive material. The siphons are cleansed by an ingenious process
invented by Belgrand and applied by him to that of the Alma,--a large
wooden ball, eighty-five centimetres in diameter, traversing twice a
week each of the two conduits, a metre in diameter. So thorough is this
policing of the sewers, that it is recorded that the number of heavy
leathern thigh boots furnished the _egoutiers_ is some twelve hundred or
two thousand annually, representing a value of nearly a hundred thousand
francs. One pair of these boots lasts about six months.

An analysis of the air of these sewers gives surprising results. The
proportion of carbonic acid is somewhat greater than in the air of the
streets overhead, that of ammoniacal azote is much more considerable,
and that of bacteria only half as great. Consequently, not only does the
personnel of this underground labyrinth traverse it constantly without
danger, but visitors from the upper world find amusement in exploring
it. Every fortnight, on the second and fourth Wednesdays of the month,
the Prefet of the Seine, or the Chief Engineer of the _Service de
l'Assainissement de Paris_, grants permits for these visits to a certain
number of applicants,--the visitors are transported through the
collecteurs of the Chatelet to the Place de la Concorde, under the
Boulevard Sebastopol and the Rue de Rivoli, in little vehicles forming
two trains, drawn each by an electric engine; then from the Concorde to
the Madeleine, under the Rue Royale, in boats drawn by an electric tug.
The trip takes about an hour, and can be made in either direction; the
sewers are open to this invasion from Easter to the end of October,
excepting in case of storms, when the water in the canals is apt to rise
rapidly over the banquettes and drive the workmen to the _regards_ or
places of ascent provided every fifty or a hundred metres apart. The
danger of asphyxia, which was formerly very serious, is now practically
abolished, the ventilation being assured by numerous openings in the
street gutters under the curb-stones, which are kept free from flo