DALY DAM 649 Medical Sciences," and has contributed largely to the " Transactions of the New York Acad- emy of Medicine," the "American Medical Monthly," and other medical journals of New York. In 1859 he published a "Treatise on Human Physiology," which immediately be- came a standard work ; and in 1868 a " Trea- tise on Physiology and Hygiene " for schools, which has been translated into French. In April, 1861, he went to Washington as surgeon to the 7th regiment of the city of New York. He was appointed brigade surgeon of volunteers in August, 1861, and resigned in March, 1864, having filled several important positions in the medical corps. As an original worker in physi- ology, he is best known by his researches on the corpus luteum, the anatomy of the placenta, the physiology of the cerebellum, intestinal di- gestion, and the other experimental observations embodied in his treatise on physiology. These, with other original investigations, have placed him in the front rank of living physiologists. DALY, Cesar, a French architect, born in Ver- dun in 1809. He is a pupil of Felix Durban, and was employed to restore the cathedral of Albi. In 1840 he founded the Revue de I" 1 architecture et des travaux publics, a richly illustrated monthly periodical. In this he has published a plan of a complete Fourierite pha- lanstery, and in 1855 he made a visit to Oabet's communist colony in the United States. His principal published works are V Architecture privee au XIX e siecle sous Napoleon III. (3 vols. fol., 1860-'64), and Motifs historiques ^archi- tecture et de sculpture (46 nos. fol., 1864-'7). DAM, an obstruction or barrage employed for raising the level of water in a stream, or for excluding it from an enclosure. Structures of the latter kind are called coffer dams, and are used to afford facilities for excavating. Dams for raising the level of water in streams have a variety of purposes, such as furnishing water power to machinery, supplying aqueducts for conveying water to towns or for irrigation, and for effecting slack-water navigation of rivers. The material and construction of a dam will depend upon its object and upon the cross section of the body of water it is intended to restrain. For still and shallow water of not more than 5 ft. depth, where the foundation is firm and comparatively impervious, an embank- ment of stiff clay, 8 or 10 ft. in breadth, and well rammed, will be sufficient, if a gate is provided to keep the level of the water below the top of the embankment and thus prevent its wearing away. Where the confined water has much depth and breadth at the dam, the construction requires great strength, and there- fore must be of. materials capable of being firmly joined together and also to the banks of the stream. Stone masonry well laid in hy- draulic cement and framework of timber, or the two in combination, are the materials usually employed in the construction of dams of great strength. When dams for slack-water naviga- tion are built upon streams which are subject to heavy freshets, the selection of the site is very important. It is generally advisable to place them where the stream is pretty wide, for the purpose of allowing a ready flow over the dam during high water. If built at a nar- row place, the restraint to the outlet would so increase the hydraulic as well as the hydrostatic pressure that great expense would necessarily be incurred in making a structure sufficiently strong and securely joining it to the banks, and in many cases the object could not be accom- plished. Sometimes the dam is built in a straight line transverse or diagonal to the cur- rent. The diagonal line allows the readiest flow, but the transverse is generally prefer- able on account of making less disturbance in the bed of the stream below. It may also, for greater strength, be built in the form of an arc with the convex surface toward the current, or it may have two or more straight lines, the angles pointing up stream. In constructing a dam, it must be borne in mind that the press- ure of water is in proportion to its depth, but the circumstances not only vary with differ- ence of location, but in the same location in consequence of changes which constantly take place in the current of the stream. Often during a freshet the surface becomes exceed- ingly rapid, so as to exert great force against the upper part of the dam, and calculations based upon hydrostatic pressure alone would prove erroneous. The rule therefore is to supplement mathematical calculations by a judgment as to the requirements necessary in each particular case, and to make the structure strong enough at every point to withstand whatever force may be brought against it under any possible circumstances. Dams are often built of a framework of timber, a plate resting upon posts which in turn are supported by a sill, reaching across the stream. Upon the plate rafters are laid, one end resting upon the plate and the other reaching up the stream and resting upon the rocky bed or upon anoth- er sill. Across the rafters planking is placed of sufficient strength to withstand the hydro- static pressure, as well as that of the running water. The dam across the Connecticut river at Holyoke, Mass., completed in 1849, is 1,017 ft. long and 30 ft. high. It is formed of square timbers inclined 22 to the horizon, having one end bolted to the rock and the other resting upon a timber framework. From the crest of the dam descends an apron 4 ft. long, which slopes also at an angle of 22. This dam has withstood the heaviest freshets in the Connec- ticut river without having given way in any part. The water is delivered by 13 gates to a main canal faced with masonry, 140 ft. wide at bottom, 144 ft. at top, and 22 ft. deep. The motive power afforded by this dam is said to be the best in the United States. The barrage across the river Furens in France, for the pri- mary purpose of forming a reservoir to hold the waters of the river during freshets from inundating the town of St. fitienne, and the
