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DALTON 250 DAM is a winter and summer health resort, and has canning factories, cotton com- presses, flour mills, foundries and ma- chine shops, public schools, weekly news- papers, a National bank, etc. It was a place of strategic importance and was nearly destroyed during the Civil War. Pop. (1910) 5,324; (1920) 5,222. DALTON, JOHN, an English chem- ist; born in Eaglesfield, Sept. 6, 1766. After teaching for 12 years at Kendal, in 1793 his reputation as a mathemati- cian won for him the chair of mathe- matics at the New College, Manchester. Here he continued to reside (though the college was removed in 1799), publish- ing from year to year valuable essays and papers on scientific subjects, while he also lectured in London, and visited Paris. In 1808 he announced ("New System of Chemical Philosophy") his atomic theory of chemical action, the discovery of which spread his fame over Europe. Various academic and other honors were bestowed upon him, and in 1833 he received a pension. He died July 27, 1844. DALY, ARNOLD, an American actor, born in Brooklyn, N. Y., in 1875. He at- tained considerable prominence by his productions and interpretations of George Bernard Shaw's plays, appearing in 1903 in "Candida," in 1904 in "Mrs. Warren's Profession," and "You Never Can Tell," in 1906 in "Arms and the Man" and the "Man of Destiny." In the season of 1911 he played at the Criterion Theatre, Lon- don, and in 1913-1914 played in "General John Regan" in New York. DALY, (JOHN) AUGUSTIN, an American dramatist and theatrical manager; born in Plymouth, N. C, July 20, 1838. Included in his original plays are: "Divorce," "Pique," "Horizon," "Under the Gaslight," and a story called "Peg Woffington, a Tribute to the Actress and the Woman." At various times during his career he managed some of the most popular and successful actors and actresses in the United States, including Fanny Davenport, Clara Morris, Ada Rehan, etc. He died in Paris, June 7, 1899. DAM, a barrier built across a stream, valley, or other depression, for the pur- pose of impounding or regulating the flow of water behind it. Dams are con- structed to supply water and water power to communities, for irrigation projects, for hydroelectric development, to make streams navigable, and for sim- ilar purposes. Dams may be con- structed of earth, timber and loose stone, stone masonry, steel, or, as has been the most general practice of recent years, re-enforced concrete. A dam must be designed to prevent failure by over- turning, by sliding at the base or at horizontal joint, by crushing (in the case of masonry dams), by fracture caused by tension, and by erosion. The head or height of the water behind the dam determines the pressure that the dam has to withstand, not the volume of water behind it. Every well-designed dam has ample provision for the easy passage of flood waters, because force exerted by an extremely large volume of water passing over the crest of the dam would possibly cause its failure. To guard against this possibility flood gates, spillways, or tunnels are used. Earth dams are made by packing suc- cessive layers of earth. The earth may be drawn in carts or buckets, and packed by rolling, or by water, or the earth may be both transported and packed by hy- draulic means. Usually, in an earth dam, the upstream face of the dam is paved with some material more resistant to seepage than earth, or the dam is provided with a waterproof lining or corewall. Earth dams vary in height from a few feet to over 100 ft., and in length from a few feet to miles. Masonry dams are constructed either of stone set with cement mortar, or of re-enforced concrete. The cross section of a modern masonry dam of the gravity type resembles in general a right-angle triangle, except that the sides are some- what curved. The approximately verti* cal side is placed upstream, the base ig liable to be rather broad, and the top rounded. Some engineers favor the use of the arch principle, either single or multiple, to resist the force of the water, and it is said that a considerable saving of material may be gained with no loss of strength. Another recent develop- ment in dam design is the hollow re- enforced concrete dam, which consists essentially of water-tight concrete slabs supported on piers. Rock-fill dams are constructed by pil- ing large stones together, and facing the upstream side with planks, concrete, or other waterproof material. Steel dams never had a great vogue, and timber dams are seldom constructed by modern engineers, except as tempo- rary structures. Dams which are built to aid naviga- tion, are usually so constructed that they may be raised or lowered. The Gatun Dam across the Chagres river, Panama canal, is an earth dam. It was partly constructed by the hy- draulic method. It is about 115 feet high and over 1% miles long. The base of the dam, which is about sea-level, is 2,020 feet wide. At the water line,