State of the Sewers and H ater Supj)li/ of Paris. 343 
tho m;u'a(l;imis(Kl boulevards their scrapings. Markets, slaughter- 
houses, barracks, paid their tribute of manure — vegetable refuse, 
blood, urine, or undiluted night-soil. This confused mass, 
mixed with water, issued from the sewer's mouth at Asnieres, 
in a thick and dark stream, flowing at the rate of 1 ton per 
sec(mil. 
To jM-()vide against the accumulation of a great mass of filth 
near the sewer's mouth, tlie following ingenious device was 
adopted : — 
The centre of the main drain is occupied by a canal 2^ miles 
long, having a fall of 1 in 2000. On this canal a barge is em- 
plo^ ed, from the fore part of which is suspended a metal flood- 
gate [vanne), which fits exactly to the sides of the tunnel up to 
a certain water-level, and lowered bv leverage to within a few 
inches of the bottom. By these means the stream is headed up 
behind the floodgate, which as soon as there is a head of two 
feet of water forces out through the small aperture left below a 
perfect torrent of refuse, sand, and even stones, which are mashed 
and rolled together, and thrust onwards in a long drift 100 yards 
in advance. 
As the barge itself is propelled slowly forwards by the stream 
which it holds in check, the torrent keeps advancing, and the 
outscourings never find a resting-place till at the end of ten 
days the mouth of the sewer is reached. The boat then per- 
forms its backward journey by the aid of floodgates lowered from 
the roof. These, acting like locks on a canal, raise the water to 
an artificial level for a distance of 11,000 yards at a time, by 
which means the barge is gradually floated back. 
The lighting and signals had still to be provided for. At 
first small lamps, such as are fixed to railway trains were tried, 
but their light was found to be too dazzling to those in front, 
whilst it left those in the rear in deep shade. A common oil- 
lamp in a glass globe, distributing its light equally around to a 
distance of ten yards, was ultimately preferred. Red, blue, and 
green railway-lanterns answer perfectly for signals. 
Thus far provision had been made for cleansing the town, but 
at the cost of the Seine, where a pestilential delta would be 
formed at the sewer's mouth. The great point was to extract all 
solid matter from the stream without interrupting its flow ; this 
alone would lodge and accumulate ; this would interfere with 
working pumps for irrigation ; liquids would float away with the 
stream, and would undergo slow combustion when in contact 
Avith the air, and vanish. 
The various solid bodies contained in the stream, though 
blended together by the flood, would not really mix or amal- 
