“2. Filtration--mechanically by artificial beds of sand, gravel, etc., chemically by charcoal, iron, etc. “3. Subsidence--clarification by deposition; storage reservoirs. “4. Aeration--spontaneous purification by oxidation. “5. Covered reservoirs--to prevent atmospheric influences. “6. Precipitation of carbonates--Clark’s System.” The infiltration system is resorted to where natural means for permeation are found; the galleries for intercepting the water being constructed in the sand or gravel banks or bed. The clarification, however, is necessarily restricted, owing to the general high rate of filtration. Lowell, Mass., has a gallery in the gravel banks of the Merrimack River, 1,300 feet in length, 8 feet by 8 feet, the bottom 8 feet below the river bed. The capacity is six million gallons, and rate of flow 150 gallons per square foot in twenty-four hours. Lawrence, Mass., has a similar gallery. Brookline’s (Mass.) gallery is 762 feet in length; 6 feet below the river bed. Rate of flow is 490 feet per square foot. Newark, N. J., tried the experiment of driven wells. They drove sixty-three-inch tubes 28 feet apart, 40 feet deep, into the bank of the Passaic, three hundred feet from the shore line. The tubes were attached to three lines of suction pipes, and the latter united in one twenty-four-inch main for the supply of their five million pump. As their expectations as to the quality and quantity of water were not realized, a well was substituted. Columbus, O., has a gallery under the Scioto River, 600 feet in length, with a capacity of eight millions daily. Toronto, Canada, has a basin excavated in an island of Lake Huron, opposite the city, 13½ feet below low water, and 3,090 feet in length; the rate of flow is 52 imperial gallons per square foot for twenty-four hours. Lyons, France, has two covered galleries along the banks of the Rhone; the area of bottoms 17,200 square feet; capacity six millions, and rate of flow at lowest stage 100 gallons per square foot. Toulouse, France, has three covered galleries along the banks of the Garonne River. The last gallery constructed is 1,180 feet long; capacity, two and a half millions; rate of flow, 228 gallons per square foot of bottom area. Perth, Scotland, has a gallery in an island of the River Tay, 300 feet long, 4 feet wide by 8 feet high, 2½ feet below the surface of the river; rate of flow, 182 gallons per square foot per diem. Genoa, Italy, has a gallery in the valley of the northern slope of the Mantine Alps, 1,181 feet above the sea level. It is 1,780 feet long, 5 feet wide and 7 to 8 feet high, and extends, in part, beneath the bed of the river Scrivia, transversely from side to side, and in part along the bank. It has a delivery of 6,412 gallons for twenty-four hours per lineal foot.