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large basin, with a surface of 16,000 square feet, and a depth of fivefeet, where it loses of course its velocity, deposits what it has in sus-pension, and passes out again by a grated opening, the bottom ofwhich is 27 inches below the surface. From there it continuesagain its course, by the canal, to a second and smaller basin near theworks. From there again it passes through a double set of wire grat-ings into a third basin, standing at the height of 45 metres, or 147feet above the receivers. All these precautions are necessary to securewater free from impurities, or foreign substances, which might be veryinjurious to the stop-cocks or valves through which it afterwards hasto pass. In the granitic regions of New England , the clear water ofour mountain streams would need nothing like this. F’rom this thirdbasin the water is let down by two iron pipes, each 0.50 metre, or 20inches in diameter,, to a reservoir built in masonry, forming the upperor second story of a building erected for the purpose, where it standsat the level of 25 metres, or 82 feet above the receivers, and close tothe building which contains them ; and it is from this last reservoirthat it is let directly on to the compressors. The object of the wholework thus far, therefore, is simply to supply water to a reservoir 82feet in height above the point where the water is to be used. Thelong distance from which it is brought, the deposit basins on the line,the height of 147 feet at which the third basin is situated, all thesewere peculiarities indicated or required by local necessities, resultingfrom the rough topography of the region, or the peculiar character ofits water.
Between this reservoir and the air receivers placed in the buildingjust below it, are the ten compressors. These are ten iron pipes, allprecisely alike, which are in free communication with the water in thereservoir, and descend froln it at an angle of about 45 degrees. Theyrest upon solid masonry built upon the side-hill, and enter the build-ing in which the ten receivers are erected. Each pipe as it enters thebuilding is turned vertically downward, as shown in the annexed sketch,and after a short horizontal course rises again vertically, and is thenplaced in communication with the upper part of the receiver, to whichit corresponds. In the vertical branch near the receiver at A [PlateXIX.] is a valve opening inward to the receiver, and which, thoughpressed on one side by the water held in the compressor pipe, tendingto open it, is pressed on the other by the confined air, which has theforce of a column af water twice as high held in the manometric pipe,and therefore keeps it tightly closed. Directly under the valve A arefour small valves, v, in the side of the pipe, by which outward air