WELLS AND WELL-BORING.
obtain the requisite supplies of water in localities desti tute of natural springs or of springs that yield sufficiently, and where the water of artificial wells is poor in quality, recourse must be had to cisterns. These watertight covered reservoirs for the storage of rain-water are placed where they- will be convenient of access and protected from beat and frost. They may be of any desired form and size, and where they are employed upon a large scale a number may be arranged side by side, in which case the division-walls between them will serve as abutments to support the structure. That the walls and bottom of the cisteni may be watertight, they are built of hard-burned bricks laid in good hydraulic cement and covered on the inside to the depth of from one-half to three-fourths of an inch with a layer of quick-setting cement. The supply of the cistern will depend upon the amount of rainfall. (See River Engineering, p. 293.) often happens that the surface of the ground will ap pear to be poorly supplied with water even though water-bearing strata may be present at comparatively slight depths, for the reason that the so-called " ground-water " reaches the surface naturally only where the ground formation is especially favorable. To utilize this subterranean water for drink-ing and household purposes, there is sunk to it a well, whose sides are properly protected from caving in. The construction of the well as sumes the simplest form when it is required to enclose the waters of a flow ing spring. The stratum of sand or gravel through which the water flows is merely excavated so far as to allow of the collection of a body of water deep enough to be taken out conveniently by baling or otherwise. The walls of these spring-wells need to be carried down only far enough to ob tain a firm foundation; to prevent the softening of the surrounding soil by the overflow, a side-channel should be provided to carry off the surplus.
wells are built either by excavating the well-shaft, lining the interior of the same with timbers, to prevent caving in, and then raising a cylindrical wall of masonry from below upward upon a tim ber foundation, the hollow space between the wooden shaft-lining and the masonry being filled in with earth, or by sinking the well if the water bearing strata are found near the ground-surface. For this purpose an
excavation is made from the surface down to the level of the water-bearing stratum, and around the wall of this excavation several stout planks are placed, one above another, upon which the wall of masonry is built. By excavating beneath the timber foundation with boring or digging tools or with the sand-pump, the cylinder of masonry is caused slowly to settle down, the walling being continued upward as fast as the sinking pro gresses, until the required depth is reached. When the well is completed, the pump, pump-tube, and other appliances are put in place.
fizells.—A driven, or tube, well, consists essentially of a strong pipe of wrought iron perforated about its lower end with a number of small holes and terminating below in a sharp point of steel (pi. 53, figs. 1-3). This tube is driven into the earth with a small pile-driver hammer (fig. 3) until a water-bearing stratum is reached. I'Vhere the depth exceeds the length of the tube, a second section is screwed to the top of the first, and the driving- is continued. When the needful supply is found, a small sue tion-pump (fig. 2) is attached to the top of the tube. This mode of obtain ing water is very widely practised throughout the agricultural regions of the United States wherever the nature of the ground will admit. The Eng lish army found driven wells very serviceable in its Abyssinian campaign. In Minneapolis, in situations beyond the reach of the city water-service, a number of such wells, placed about 15 feet from a centre, with their deliv ery-pipes joined at the top, are used to obtain a supply of water for extin eruishino- fires.