The city of Glasgow made two failures in attempting to furnish a supply by this system. The first experiment was the construction of a reservoir on the northern bank of the Clyde, below the level of the river. Beneath the bottom of the reservoir was thirty-two-feet cylindrical tunnels made of wedged-shape bricks without mortar. The failure was due to the inability to keep the interstices free from the deposit of impurities. In the second plan, they excavated shallow wells, 10 feet in diameter, 6 feet deep, and 20 feet apart, in the stratum of sand adjacent to the river. The wells were connected by pipes. The scheme was a worse failure than the first one. It often happens, as in the case of Waltham, Massachusetts, in locating these galleries, that spring water is intercepted in place of the desired water of the flowing stream. The difference in temperature and increased hardness of the spring water, determine the class of water. FILTRATION is the artificial method of clarification by mechanical and chemical means. By the mechanical system heavier impurities are held in suspense by percolation of water through carefully prepared beds of sand, gravel, coke, shells, and like substances. The total area of the London filter beds in 1874 was 68 acres, and rate of filtration per hour in inches and depth of water, or head on beds, were: RATE. DEPTH. Lambeth Works 10 inches. 7 feet. Southwark & Vauxhall 4 “ 4 “ Grand Junction 3 “ 4 “ West Middlesex 4 “ 3 “ Chelsea 6 “ 5 “ New River 4½ “ 5 “ East London 3 “ 5 “ The efficiency of filtration is inversely to rate of flow. Humber says: “It is now generally admitted that filtration through sand, to be effective, should not proceed at a higher rate than 6 inches of descent per hour; or, in other words, there should be at least 1½ square yards of filtering area for each 1,000 gallons per day. This is, of course, exclusive of reserve area, which will be necessary to permit of at least one bed being cleansed while sufficient area remains in operation in the other beds.” The maintenance of these beds enhance the cost of supplying water, because they must be cleansed frequently--in some cases once a week. The regulation and control of the water consumption is an important consideration, that the rate of increase will be proportioned to the growth of the city; and not, as in this country, an unaccountable rapid increase due to the profligate use of water that makes filtration impossible. Over eleven-twelfths of the water supplied to London is filtered with the following efficiency: