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Earthenware pipes may be used for water conduits, provided the joints are not placed under pressure.

Aqueducts of iron will, probably, be cheaper than masonry or brick-work constructions.

Water may be brought in by gravity; that is, water obtained at a distance may be found at such an elevation above the district to be supplied as to allow of its flowing through conduits or pipes to the tanks or cisterns from which it is to be distributed. A fall of five feet per mile is sufficient for a conduit of two feet diameter. Conduits of larger diameters may have less fall, down to six inches per mile, as on the New River, London.

Well-water will vary in purity according to the nature and the soluble matters contained in the ground from which the well derives its supply.

Shallow wells are always liable to pollution from vegetable matter, or even from animal matter in the surface soil. Deep wells only, i.e., wells of a sufficient depth to afford water of the requisite purity, should be sunk; and the surface-soil water should be cut off from the deep water by casing the well above.

Salt rock is found in the new red sandstone forma. tion. There is risk in deep sinking from this cause; .but good water is frequently found in the new red sandstone.

A spring is the lowest point or lip of an underground reservoir of water in the stratification. A well sunk in such strata will most probably furnish, beside the volume of the spring, an additional supply of water.

Natural springs may be utilized by storing the water in a reservoir which will contain the flow of one entire day, or longer period.

Such reservoirs should be walled with masonry, and may be covered in to protect the water from contamination.

Springs of water at a distance may be conducted in channels contouring the intervening distance.

The fall for a conduit may vary according to circumstances. The fall should not be less than one in 10,000 nor greater than one in 300, unless cast-iron pipe conduits are used.

In forming an earthenware pipe conduit great care must be taken to make the trench water-tight, and then to lay and joint the pipes so as to secure that the conduit shall be sound and water-tight through its whole length, to prevent leakage into the subsoil, and to obviate the risk of impure water from the subsoil entering the pipe.

In forming a conduit the pipes should be laid in straight lines, from point to point. There should be means of inspection and ventilation in each quarter mile, and of washing out at all convenient points.

Valley lines may be crossed by means of cast-iron syphon-pipes; that is, a pipe may be laid across a valley to conduct the water under pressure.

All valley or syphon-lines should have double the fall in their length of the ordinary conduit.

There should be means provided to wash out and cleanse such syphon-pipe or pipes.

CHAPTER XII.

DRAINAGE DEFECTS, AND HOW TO REMEDY THEM.

COMPLAINTS of nuisances arising from defective drains will occupy much of the inspector's time in making investigations in reference thereto. The draining of all dwellings and the sewering of all urban districts must be understood as work that cannot be shirked. It is, therefore, essential for the inspector to make himself conversant with the acknowledged laws and conditions of good drainage, not that it will be a part of his duty (only in special cases) to carry out a system of sewering or draining, but for the purpose of enabling him to detect the defects in existing drains when making his regular inspections (a).

In passing, I might remark that the inspector will do well never to allow bell traps to be used.

The reader cannot do better than thoroughly digest the following twenty-three articles, which are extracted from a work entitled “Suggestions as to Preparation of Plans as to Main Sewerage and Drainage, and as to Water Supply,” by R. Rawlinson, Esq., C.E., C.B., Chief Engineering Inspector to the Local Government

(a) Sulphuretted hydrogen gas escaping from a sewer is a nuisance : see Woolrych's Metropolis Local Management Acts, p. 609. built over,

Board, and who kindly gave me his permission to make these extracts :

1. Natural streams should not be arched over to form main sewers; because a natural stream may

drain an area very much larger than the area

and consequently a culvert (or sewer) of capacity to remove flood waters in a wet season would be comparatively dry during a dry season, and any sewage then flowing in would stagnate and evaporate, causing nuisance.

2. Valley lines, natural streams, and surface areas may be improved, so as to remove more readily surface water and extreme falls of rain; that is to say, streams filled up by accumulations of refuse may be cleansed and deepened, and areas liable to be flooded may be raised or be protected by embankments.

3. Main sewers need not be of capacity to contain flood-water of the area drained, as such flood-water should be passed over the surface (a).

4. Main sewers should be laid out in straight lines and true gradients, from point to point, with sideentrances, or with manholes, and flushing and ventilating arrangements at each principal change of line and gradient. All manholes should be brought up to the surface of the road or street to allow of inspection, and should be finished with a cover easily removable. When sewers are laid out in “straight lines," and the surveyor insists upon absolute truth of workmanship both in line and in gradient, the work will necessarily be well done. With manholes and lampholes at each

(a) Foul drain a nuisance (metropolis): see section 8, Nuisance Removal Act, 1855.

change of line or of gradient, the surveyor, by remov. ing the covers, can at any time set out the central line of the sewer upon the surface, and can ascertain the depth from the surface to the sewer at any intermediate point, and so find the exact position of any side junction (6).

5. Duplicate systems of sewers are not required. Existing road-drains and drains to natural streams in valley lines may be retained for storm waters, and may be improved, or, if necessary, enlarged. Two sets of main sewers with two sets of house-drains will be costly to construct, and, if constructed, will often lead to -complications tending to defeat the proposed uses. The so-called clean water sewer cannot, in many cases, be large enough to receive storm-water, and in dry weather it would of course be dry. The sewer proper would be without the flushing and cleansing given during falls of rain, and the washings off land, ditches, roads, roofs, yards, and gutters, during the first falls of heavy rain, would, in many cases, be as polluted as the sewage in the true sewer. Supposing two sewers in a street, and two sets of drains from each house on each side of such street, the drains must interlace the duplicated sewers, the foul water drain communicating with one, the surface water drain with the other. Under such circumstances it would be almost impossible to prevent builders and workmen from entering the sewers with their drains indiscriminately. Moreover, if the duplicate sewers were not absolutely water-tight,

(6) Foul drain a nuisance (England, except metropolis): see section 91, Public Health Act, 1875.

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