dimensions, and the water flows into them only at certain regular periods, by the opening of valves, fixed for that purpose at convenient places on the principal mains, which convey the water along every street. This kind of machine is commonly constructed of an iron frame, with a smooth iron plate accurately fitted to slide up and down in a groove, and attached to a screw, which raises or lowers it, so as to permit the water to fill the cisterns, or stop the current when they are properly supplied. It is usually called a screw or slide valve. For the purpose, also, of regulating the flowing of the water to the cisterns, each small pipe, employed for conveying it from the mains, has a brass cock affixed to its extremity. The valve of the cock has a square projecting pin, to which is attached a copper rod with a globe or ball adapted to rise and fall, so that its ascent, by the filling of the cistern, closes the opening when it is quite full.

Though the natural tendency of water be to flow down a declivity, yet the levels of different parts of many towns are very irregular, and therefore require the pipes to be placed either in ascending or descending directions, according to circumstances, so as to adapt them to dif ferent situations. The course of the water being thus rendered undulating, its current sometimes encounters interruptions by the air disengaged from it collecting in the pipes, and this particularly occurs when they are not kept completely filled. Hence, contrivances are necessary for its discharge; and one of the methods employed is that of opening the orifices,-called plug-pipes,-which afford the supply of water on occasions of fires. The same object is effected at Edinburgh by means of circular cast-iron boxes, about four feet high, and one foot and a half in diameter, which, being affixed at the summit of each declivity, are opened by the surveyor of the works,

every two or three days, in order to allow the air to escape without any loss of water.

The sources whence different places derive their supply are so various as to be deserving of notice. At Liverpool it is obtained from abundant springs in its vicinity; but at Manchester it is collected from the lands surrounding the reservoirs, which are constructed to receive and preserve it for distribution; whilst an exuberance is procured for Greenock from the small streams, which the dews and rains produce in the neighbouring mountains. London and Glasgow are chiefly supplied by the grand rivers on the banks of which they have their respective

sites.

The water furnished to Edinburgh, and in part to Liverpool, being conveyed directly from springs, is naturally pure and limpid; and the abundance flowing to the former enables the inhabitants to have the use of it without limit or restraint. But according to an estimate made of the quantity that each inhabitant of the respective places daily receives, it amounts, on the average, at London, to about ten gallons,-at Glasgow, twelve,—at Edinburgh, seven and a half,—at Manchester, five and a half,—and at Liverpool about three and a half gallons. Glasgow, Greenock, and that part of London in the Chelsea Company's district, are supplied with filtered water; and the extensive and complete success of the operation at these establishments, will probably lead to its adoption at every other, where the water is obtained from rivers. The practice indeed appears indispensable, in order to obviate the objections of the fastidious; and though it would occasion some addition to the charge for it, the cost would be a trivial consideration compared with the advantage of a constant supply of pellucid water. The prices for it vary in different places, and even in the

same place, according to circumstances, but in every one they are moderate for the advantages afforded.

At London, Liverpool, Edinburgh, and several other considerable places, the principal establishments have provided the means of supplying water to all the different stories of the highest houses, within the limits of their distribution; exclusive of an abundant quantity for every useful purpose, extinguishing fires, &c.; hence their operations are the most complete and effective of their kind. As works of this description evidently afford the means of easily obtaining a plentiful supply for any important object, the expectation may, perhaps, be confidently indulged, that wherever they are constructed, the inhabitants will be stimulated to construct capacious and convenient baths for their general accommodation. The utility of such contrivances would be obvious, in their tendency to promote the healthful and cleanly practice of bathing. Hence, the habit might become common both among the refined and less cultivated residents of Britain, so that even in this particular, we might challenge a comparison with the people of any other country, on the surface of our habitable globe.

It has been estimated that the iron pipes of different dimensions, laid in various directions, to supply London and its vicinity, measure from one to two thousand miles. Probably all towns having a large population, will eventually adopt plans similar to those for supplying the metropolis, and propel water from comparatively low situations into lofty reservoirs, from which it can be most conveniently, readily, and cheaply conveyed to the inhabitants, for domestic and other purposes. If great profit do not accrue to the persons who may first engage to furnish the capital for accomplishing such important works, it may be fairly presumed that the results will