THE USE OF GROUND-WATER.[65] Ground-waters are extensively used in Europe, and apparently in some localities the geological formations are unusually favorable to this kind of supply. Paris derives all the water it now uses for domestic purposes from springs, but has a supplementary supply from the river for other purposes. Vienna and Munich also obtain their entire supplies from springs, while Budapest, Cologne, Leipzig, Dresden, Frankfurt, many of the great French cities, Brussels, a part of London, and many other English cities derive their supplies from wells or filter-galleries, and among the smaller cities all over Europe ground-water supplies are more numerous than other kinds. APPENDIX X. LITERATURE OF FILTRATION. The following is a list of a number of articles on filtration. The list is not complete, but it is believed that it contains the greater part of articles upon slow sand-filtration, and that it will prove serviceable to those who wish to study the subject more in detail. ANKLAMM. Glasers Annalen, 1886, p. 48. A description of the Tegel filters at Berlin, with excellent plans. BAKER. Engineering News. Water purification in America: a series of descriptions of filters, as follows: Aug. 3, 1893, Lawrence filter and description of apparatus of screening sand and gravel; Apr. 26, 1894, filter at Nantucket, Mass.; June 7, 1894, filters at Ilion, N. Y., plans; June 14, 1894, filters at Hudson, N. Y.; July 12, 1894, filters at Zürich, Switzerland, plans; Aug. 23, 1894, filters at Mt. Vernon, N. Y., plans. BERTSCHINGER. Journal für Gas- und Wasserversorgung, 1889, p. 1126. A record of experiments made at Zürich upon the effect of rate of filtration, scraping, and the influence of vaulting. Rate and vaulting were found to be without effect, but poorer results followed scraping. The numbers of bacteria in the lake-water were too low to allow conclusive results. —— Journal für Gas- und Wasserversorgung, 1891, p. 684. A farther account of the Zürich results, with full analyses and a criticism of Fränkel and Piefke’s experiments. BOLTON. Pamphlet, 1884. Descriptions and statistics of London filters. BÖTTCHER and OHNESORGE. Zeitschrift für Bauwesen, 1876, p. 343. A description of the Bremen works, with full plans. BURTON. Water-supply of Towns. London, 1894. Pages 94-115 are upon filtration and mention a novel method of regulating the rate. CODD. Engineering News, Apr. 26, 1894. A description of a filter at Nantucket, Mass. CRAMER. Centralblatt für Bauwesen, 1886, p. 42. A description of filters built at Brieg, Germany. CROOK. London Water-supply. London, 1883. DELBRUCK. Allgemeine Bauzeitung, 1853, p. 103. A general article on filtration; particularly valuable for notices of early attempts at filtration and of the use of alum. Deutsche Verein von Gas- und Wasserfachmänner.