SOMERSWORTH, N. H. Designed by William Wheeler. These were the second vaulted filters to be built in the United States. The supply is from the Salmon Falls River and flows to the filters by gravity, the filters being below the river level. Description: Eng. News, Vol 40, p. 358; Eng. Record, Vol. 38, p. 270. BERWYN, PENNA. Designed by J. W. Ledoux. These open filters are used for filtering creek water. Description: Eng. News, Vol. 41, p. 150. HARRISBURG, PENNA. (State Lunatic Hospital.) Designed by Allen Hazen; open masonry filters, used for treating the water from a small creek which is often muddy and is subject to pollution. No published description. ALBANY, N. Y. Designed by Allen Hazen. Constructed 1898-99. This was the third and is the largest vaulted masonry filter plant yet constructed in the United States. It is used for filtering the Hudson River water, which is slightly muddy and much polluted by sewage. Description: Eng. News, Vol. 39, p. 91; Vol. 40, p. 254. ROCK ISLAND, ILL. Designed by Jacob A. Harman. Open filters with embankments, used for filtering the Mississippi River water, which is very muddy and also polluted by sewage. No published description. * * * * * CAPACITY OF FILTERS. Estimating the total additional area of sand filters for which figures are not available at 100 acres, and the maximum capacity of sand filters at three million gallons per acre daily, and of mechanical filters at three million gallons per thousand square feet of filtering area, the total filtering capacity of all the filters in the world used for public water supplies in 1899 is nearly 1600 million gallons daily, of which 15 per cent is represented by mechanical filters and 85 per cent by sand filters. In the United States, including Wilmington, the total filtering capacity is nearly 300 million gallons daily, of which 18 per cent is represented by sand filters, 79 per cent by mechanical filters, and 3 per cent by a special type of filters. APPENDIX V. LONDON’S WATER-SUPPLY. London alone among great capitals is supplied with water by private companies. They are, however, under government supervision, and the rates charged for water are regulated by law. There are eight companies, each of which supplies its own separate district, so that there is no competition whatever. One of the companies supplying 460,000 people uses only ground-water drawn from deep wells in the chalk, but the other seven companies depend mainly upon the rivers Thames and Lea for their water. All water so drawn is filtered, and must be satisfactory to the water examiner, who is required to inspect the water supplied by each company at frequent intervals, and the results of the examinations are published each month.