SEW

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t Vi?' ears ' O n this one occasion, at Earl-street, the dis-a hove 300 cubic feet per minute, and as a similar

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'liat „ ) ' V ,’ S recorded in Upper George-street, we may reckon?* a Son . discharges are not unfrequent during the rainy,llst an ’ We mLrst not forget, however, tliat the pipes in these, ea Were connected with an imperfect system of colla-rains > and that under a perfect system, the surface-^ld ' V ° u ^d have been carried off more rapidly, and tlieref i>ttl^ 0t ^ ave * 3een 80 8 reat an accumulation at this point.,. ex P e rie nce of the working of a perfect scheme of thisfa :! l< ? n > would readily determine the requisite sizes.

•\| s ain lines of sewer, and where they pass under mainSuch * s ^ ou ld recommend the construction of brick sewersN f 0p Slze 38 would be sufficient for the passage of a man,a ot r °om to work in when requisite. In these we would% 0 f ® n iy a pipe-sewer of sufficient capacity for the usual'-able • ater > hut also the gas and water-mains, where prac-tical? 11 0r ^ er t0 obviate any necessity for breaking up theSt tK- 0n occasion ofk 6 toad! arran g ement is

r by * 8°°d roads while they are constantly being brokena Sr a an d water companies. The expense of this system,

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repairing, &c. We are convincedof considerable importance, wheremuch traffic, for it is impossible to

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re gards the sewers, would not be much greater thanv-fit nt > and there can be no doubt but that the manage-X. ’'he roadways would be much more economical.sa ch ‘ 3

circumstances, it would be worth while to con-p e „ 8iv eo°d solid roadway, whicli, though a little more

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t j ec e 111 the first outlay, would in the end prove much^1'iifi^ n °tnical, not only as regards the repair, but also asnCge ® a less amount of tractive power, and doing less

.it 4 ii 0 the vehicles passing over it. It is very advisable,

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°terranean works should be treated of together as

„ in of one system. The pipe-sewers should be

inflow 6 lnv ert, and might be so arranged as to allow of anlnt ° the large sewer, when requisite ; or the watert! > ' 8 Khl^ JOl,re( l back, for the purpose of flushing, when deemed^Po Se \ . Access would be obtained into the sewer, for the>ii at *Ces lns P ec ting and repairing the various pipes byside-r ’ as a ‘ P re sent ; and the sewer ventilated by shaftstill ^ c ways, without detriment to public health, the pipesKtirT Whi a? ‘he sewage being impermeable. The only diffi-Hjj Petits the application of this system to main roads

“Pted i ’ 18 *‘ 8 expense ; were it not for this, it might beMi f ever y street with much advantage,sjj ' c h ** 8 of large sewers have been adopted, but thatto be best adapted for the purpose, is the egg-iy'Kg ^ *ch was introduced by Mr. Roe ; the older forms!ijK8 et ? st ‘y a semicircular crown, with upright side-walls,O 1 eff' eo ? lrcu ‘ ar °r flat segmental invert. Tlie main improve-t£ ‘he ■ et * by the egg-shaped sewers, consisted in narrow-an thereby contracting the lower part of theSt^'ty and lncieas ' n g the depth of flow, by which means the"’lii c | | Scour was much improved ; the same quantity of0 p n tboved but sluggishly when spread over the widea flat invert, being now concentrated in a narrow

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\l^ ter at’ S rtla< ^ e *° move with accelerated flow ; in short,'° n bad a similar effect to that produced by thei of small pipe-sewers. Another advantage■ a g; V p ‘bis form, was the attainment of greater height■Sate area > which enabled men to pass through themr facility ; it must be confessed though, that theK« tn 0l . e er ‘ ' s rather inconvenient to walk upon. TheVsKMo Ver > is economical, and based on sound principles

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v*i>ap e ^Portions, and many methods of describing the't„ lt ’ *ave been observed at different places, some being5 p

constructed with a semicircular top, flat segmental sides, anda sharp segmental invert; the curves of the sides andinvert varying according to varying proportions of heightand width, and other circumstances. Others are constructedwith six centres, the upper part being described with tworadii, instead of being semicircular. Of all the varieties,however, the most eligible is thus described :—Let theheight of the sewer be to the width as 3 to 2 ; then havingdescribed a semicircular crown with radius 1, with radius 3,equal to the height, and with the centre on the springing-line, describe a segment touching the semicircle alreadydescribed ; for the invert, with a radius ^ or ^ of the entireheight, describe a circle which will be found to touch thesegments just described. This form is generally appli-cable, and has the advantage of being drawn to certainproportions.

The above are the most usual forms for sewers, but occa-sionally the levels will not allow sufficient height for thembeneath the roadway; and in such cases, it is necessary, forthe purpose of obtaining sufficient capacity, to construct themof a cylindrical or elliptical form ; but even then, the sameend may frequently be obtained by placing two or moreegg-shaped sewers side by side. Where there is a largeand constant flow of water, cylindrical sewers are notobjectionable.

The above sewers, if not more than 4 feet in height, and if ingood building strata, may be constructed of half-brick work,but in other cases require to be a whole brick thick, unless,the sewer be verysmall. They are constructed mainly of stock-bricks in mortar, the invert or lower portion only being laidin cement; the inverts are usually formed in blocks in cementbefore they are finally laid in the sewer ; the invert consist-ing of three or more blocks, according to its dimensions.Sometimes blue vitrified bricks are used for the invert; theyare very hard and durable, but do not adhere well to thecement. It has been proposed to construct sewers withradiated bricks, and they probably might be used withadvantage where the curve is sharp: the joints of commonbricks are very open in such cases. Radiated hollow brickshave also been suggested, and, if moderately cheap, theymight doubtless be employed successfully.

The pipe-sewers, as at present made, are of a cylindricalform ; they are constructed in lengths of 2 or 3 feet, andhave a socket at one end for the adjoining pipe to fit into;sometimes, however, they are made with half a socket oneither pipe, and this is of advantage in facilitating theirremoval, if at any time they be required to be taken up.With the whole sockets, it is difficult to take them up with-out breaking them, and it is almost impracticable to replacethem correctly after removal.

If whole-socket pipes be generally used, we should advisethe occasional adoption of half-sockets, so that in case ofstoppage, or other accident, they may admit of easy removaland replacement, without either destroying the pipes or dis-turbing the adjoining ones. Cylindrical pipes are made from3 to 2 feet in diameter. It has been suggested, that suchpipes should be made of the egg-shape, rather than cylindri-cal; but it must be borne in mind, that the contraction ofthe invert is not of so much consequence in a small pipe, wherethere is likely, at all times, to be a large current comparedwith the capacity of the pipe ; and if the pipe be generallyfull, we know that the circumference of a circle contains alarger area than the same extension of boundary-line arrangedin any other form ; therefore, if a cylindrical pipe be full,there is less frictional surface than in any other kind of pipeof the same capacity. As, however, in present practice, tlieflow of wafer varies to a great extent at different times, it