18 ANNUAL OF SCIENTIFIC DISCOVERY. 



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low the ground, and drains an area of fourteen square miles. The 

 Middle Level, as being lower in the valley on the slope of which Lon- 

 don is built, is laid at a greater depth, varying from thirty to thirty-six 

 feet, and even more below the surface. This is nearly complete, and ex- 

 tends from Kensal Green to Bow. The Low Level will extend from 

 Cremorne to Abby Mills, on the marshes, near Stratford. At Bow, the 

 Low Level waters will be raised, by powerful engines, at a pumping sta- 

 tion, to the junction of the High and Middle Level ducts, thence descend- 

 ing by their own gravity through three tunnels to the main reservoir and 

 final outfall. These three tunnels are each nine feet six inches in diam- 

 eter, and nearly four miles long. Great engineering difficulties existed 

 in the construction of these main arteries, as, from the height at which 

 they all meet, it was necessary to take them above the level of the marshes 

 leading to Barking For a mile and a half the embankment which en- 



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closes the three tunnels is carried on brick arches, the piers going eighteen 

 feet below the surface, and being based on solid concrete. In the marshes 

 at Barking, a reservoir for the reception of the sewage of the north 

 side has been formed. This reservoir is a mile and a half long by one 

 hundred feet wide, and twenty-one feet deep. It is made of this great 

 length in proportion to Avidth to allow of its being roofed with brick 

 arches, which are again covered with earth to a considerable thick- 

 ness, so that not the slightest smell or escape of miasma can take 

 place. This is capable of containing more than three times the 

 amount of sewage which can enter it while the pipes are shut, and 

 thus, when all is complete, the works will not only be large enough to 

 take off all London's sewage now, but its sewage when London is 

 double its present size. 



"While the sewage is in the reservoir we have spoken of, it will be 

 completely deodorized by an admixture of lime. When the tide is at 

 its height the sluices which pass from the bottom of the reservoir far 

 out into the bed of the river will be opened, and the whole allowed to 

 flow away. It takes two hours thus to empty the reservoir, by which 

 time the tide will be flowing down strongly, and will carry its very last 

 gallon a distance of thirteen miles below Barking, which, being itself 

 thirteen miles below London, will place the contents of the sewers, 

 every twelve hours, twenty-six or more miles distant from the metrop- 

 olis. Thus, instead of letting loose the rankest of this great city's 

 abominations in the very midst of London, and leaving it to stagnate, 

 or, still worse, to be agitated backwards and forwards in a small body 

 of water, it will all be'carried away a distance of thirteen miles, then 

 deodorized, then suffered to escape into a body of water more than a 

 hundred times greater than that into which it now crawls, and thus 

 disinfected and diluted, so as to be without either taste or smell, swept 

 still further down the stream, till every trace of it is lost. 



" On the south side, the three great sewer arteries are constructed on 

 similar plans, - - the High Level, from Dulwich to Deptford ; the Mid- 

 dle, from Clapham to Deptford ; and the Low Level, from Putney to 

 Deptford. At this point is a pumping station, which raises the water 

 from the low to the high level, whence it flows away through a ten feet 

 tunnel to Crossness Point. One part of this tunnel, passing under 

 Woolwich, is a mile and a half in length, without a single break, and 

 driven at a depth of eighty feet from the surface. At the outfall will 



