MECHANICS AND USEFUL ARTS. 17 



we have said, it could only escape at dead low water, when the return- 

 ing tide immediately churned it up the river, keeping all its abomina- 

 ble 'flotsam and jetsam' above bridge till the tide ebbed out, finding 

 200,000 or 300,000 gallons of filth to be operated upon in a similar 

 manner on its return. This was the arrangement twelve years ago, 

 and is almost entirely so still ; but, even bad as this was, it was capa- 

 ble of being made worse, and worse accordingly it was made. In 

 1849, most of the houses in London had cesspools attached to them, 

 and a very large proportion were without any drains at all. The 

 alarming nature of this evil showed itself slowly but surely in the Bills 

 of Mortality, and the then Commissioners of Sewers, who were feebly 

 battling with the evils of the drainage system, set to work to mitigate 

 the cesspool danger by drainage, making the Thames, as usual, the 

 general receptacle. From thtit time to the present some 700 or 800 

 miles of new drains have been made, and all cesspools made to drain 

 at once into the river. By this ' improved ' drainage some 200,000 

 additional gallons of sewage were daily added to the Thames at low 

 water, containing no less than 300 tons of ' organic matter,' which in 



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this case is the scientific term of filth. The result, as a matter of 

 course, has been that in the summer months the stench from the river 

 has occasionally been intolerable. In 1857, great quantities of lime 

 and chloride of lime were put in daily; in 1858, the same expedient 

 had to be resorted to again ; and in 1859, the dose had to be increased 

 into 110 tons of lime and 12 tons of chloride of lime, costing 1,500/. 

 per week. Even in a pecuniary point of view, however, this was not 

 the only evil of the system. The Thames in hot weather runs short 

 of water ; and when there is no rain, the collections of refuse in the 

 sewers have to be flushed into the river by artificial means. This 

 flushing alone during summer costs 20.000/. a year to get the poison 

 into the TTiames, where 20.000/. more is generally required to keep it 

 from breeding a plague." To obviate these difficulties, an immense 

 new sewage system was devised, and for the last few years has been in 

 the course of construction, whereby London will be effectually drained, 

 and the Thames purified. As may easily be imagined, it is impossible, 

 in an article like the present, to give more than an outline of this great 

 plan, which- may best be briefly described as consisting of three gigan- 

 tic main tunnels or sewers on each side of the river. These completely 

 divide underground London, from west to east, and cutting all existing 

 sewers at right angles intercept their flow to the Thames, and carry 

 every gallon of London sewage under certain conditions into the river 

 at a point far below the city limits and not far distant from the sea. 

 " These main drains are called the High, Middle, and Low Level sew- 

 ers, according to the height of the localities which each respectively 

 drains. The High Level, on the north side, is about eight miles in 

 length, and runs from Hainpstead to Bow, being at its rise only four 

 feet six inches in diameter, and thence increasing in circumference, as 

 the waters of the sewers it intercepts require a wider course, to five 

 feet, six feet, seven feet, ten feet six inches, eleven feet six inches, 

 and at its termination to twelve feet six inches in diameter. This 

 drain is now entirely finished, and in full work. Its minimum fall is 

 twelve feet in the mile ; its maximum at the beginning nearly fifty 

 leet a'inile. It is laid at a depth of from twenty to. twenty-six feet be- 

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