SEW

415

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ebb a °. Vem ent of 3 miles is made towards the outlet everyflow. This conclusion has been arrived at without**Per ,ent ^ ata ’ ^ or ^ ^ as s ' nce been established by actualgr a( j e ® e nt, that not only is there a progressive and retro-' ' es tl ] ot ’ on going on every tide, but that the same processplace with a series of tides, and that after a float hasa cer tain progress down the river by the excess of the*ip ^ ei [ Bie reflux, it turns, and makes an actual retrogression9f)'i Ve r,v er, by the excess of the reflux over the flux, until itfv ° nce more nearly up to the point whence it started.

!>e a 01 Hos it will appear that, in a tidal river, there willdifficulty in carrying refuse matters to sea, or even°rHeap 6 v ' c ' n > t y of towns, if it be allowed to discharge at'Vac ( ] 3 r ^ le town ; it will constantly be carried about back-o r atld ^ 0I wal ’fl s > an A depositing its solid matters in the° n the banks, of the river. The sole remedy for thislow „° be, to extend the sewer to such a distance from the

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c ar ° r .^’ sc b ar ge, that the tide may not at any time be able•Oakg 1 ? back near the town. Another object will be, to

to

^sib]^* 6 ^’sobarge at high-water, or as near high-water ass .° that it may have all the advantage of the first

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>ible,

; U| S( f ; (> '^'bis, however, is not always practicable in low-lyingj e re . a > unless, indeed, we employ artificial means for raising; jr^ 11 reaches the outlet.

n ° w cons ’fler the question under another aspect ;Kw l ' le refuse to be turned to account for agricultural^f°babl S1 though somewhat more complicated, we shallq ^ ®nfl more easily dealt with than the previous case.

a S‘ ain res °t ves itself into two distinct parts,—• ' v ^ ere the sewage is used in a liquid state, the other" 11 undergoes a preparation previous to use, and is

tied

two will require some-The first arrangement, where the

at <pji n a Ary state,—and theseI^Hure ■ rent treatment.y°Urho ex pen (led entirely upon the surrounding neigh-

. 6r of tij tuust depend, in a great measure, upon the charac-|^ltitle] ne ighbourhood, and the comparative levels betweento j? j°' vn to be drained. In this case it will be advisa-> n<J . ,v ‘d e the town into different drainage levels, cor-jVuict'i® w * t ' 1 the general or average altitudes of eacho ^ ie ac li aeent country, and provide each

w ith a separate outlet, situated as near thekef j, uing level of the adjacent land as may be inpile ext^ eCtS conven ' ent - By so doing we shall dispense toa ace s e f 1 w ' ( b the use of pumps, and other expensive con-8 ^nbl or ra ising the manure; we shall also save a con-i'^ am ount of excavation, and avoid very large maina C S8 '• must not be supposed, that here, or in any other^Plicoti “‘is article, we lay down fixed rules of universalv^i'allv 0 ’ ^ ut rather throw out hints which may be found| d/-^ se ^ul ; the peculiarities of each particular localityv %liti e8 e tbe method of drainage ; there may be someb^’bere the above d irections may not only be unad-i r ar d 1 Sl mply impracticable, and we only bring them for-is V e *hey may not be left out of consideration in anyIaa y be adopted when found to be eligible. It

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oj • 6te tb e ° ^uub of laying down positive rules in such cases,b]y v ar n . atl fre of the subject to be treated of must neces-^ j ^ ,n individual instances.

i s St Case w bich we have to consider is, when theatl( j .be applied for agricultural purposes in a drytb ree bis will, we think, prove to be the most simple of^u ct jj . have here only to collect the sewage, andinfest c ln *° one or more tanks, in such situations as maypotion foment, where it will undergo a process of dis-V 6 °i' co 311 ^ be precipitated, or solidified for the pur-6 bejgu, Ve y ance to such lands as may require it, either inourhood, or at a distance. It will be advisable

that the tanks be at some distance from the town, to obviateany danger or inconvenience which may arise during the pre-paration ; and it is further to he desired, that they should benear a canal, river, or railway, so as to present facilities forcarriage to distant localities ; it would be well if they couldbe placed in proximity to both rail and river, for while theformer will be very convenient for the purpose of conveyance,the latter will be further useful for the discharge of thesewage-water which remains after the extraction of the solidmatter, if, indeed, it be not applied to some more useful pur-pose. This water may be discharged into the river withoutinconvenience or danger, for if not already sufficiently puri-fied, it would be no difficult matter still further to purify itby filtration. If a ready means of discharge for the super-natant water be provided, the size of the tanks may be greatlydiminished, and in the same, or rather greater, proportion,the expense and difficulty of their construction.

We have now considered the subject as regards the threedifferent methods of disposal of the refuse most likely tooccur in practice. We must again express our regret thatgreater labour has not been bestowed on the question of thepracticability of the two last methods, yet at the same timewe must take occasion to remind the reader, that even hadthis question been generally disposed of, it would not followthat any particular practice would be advisable in everyindividual case. The proper determination of the methodto be adopted, must be the result of a careful investigation ofthe nature of the several districts to be drained ; one methodmay be convenient in one place—another, a different one, ina second. We have here considered the subject solely asregards the disposal, and principally with reference to outlets,as these are the most affected by the various methods ofdisposal; let us now turn to the principles of town-drainagegenerally.

The first thing to be done in laying out a system of drain-age, is to prepare a carefully surveyed map of the district tobe drained, showing at least the main levels: at the outset,perhaps a block plan will be sufficient; but before the ques-tion is finally determined upon, and details entered into, itwill be necessary to have the blocks filled in. To do this,it will be requisite that the map be on a sufficiently largescale; that adopted by the Ordnance Survey , five feet to amile, or one somewhat larger, will be found convenient, andon this, additional levels must be laid down before enteringinto detail. It will be advisable ere commencing the con-sideration of the subject, to prepare from this a map on areduced scale, containing in addition some considerable por-tion of the surrounding country, so that the consideration maynot be confined to a limited space, without reference to thecircumstances of the more immediate neighbourhood ; by sodoing, much future trouble and expense may be avoided;by all means let the consideration of the subject be compre-hensive. It will greatly assist, if the contour-lines be laiddown on this map, so as to afford at a glance a tolerablyaccurate idea of the nature of the ground. It will be furthernecessary to obtain information respecting the geology of thedistrict, as well for matters of construction as for other pur-poses, and also some general notion of the nature of the soilwith reference to agricultural matters, in order to determinethe extent to which the town-refuse may be employed asmanure in the immediate vicinity. These, however, andother matters necessary to be known, will naturally suggestthemselves to those engaged in such works.

The surveyor having made himself thoroughly acquaintedwith the character of the district to be drained, will be in a pro-per position to determine the system upon which to commenceoperations. The practice of our predecessors has been, to collect