Page:The New International Encyclopædia 1st ed. v. 05.djvu/873

* DAMROSCH. 757 SAMS AND IIESEB.VOIBS. German opera in New Y'ork City, at the Metro- politan Opera House, notwitlistanding the ob- vious ditlioulties of the undertaking. Among the operas given, Fidelio, Taniihiiuser, Lohengrin, and Dk Walhiire were the most important as comparative novelties. He died in Xew York, and imposing funeral services were held in the Opera House. His works comprise several can- tatas, a festival overture, beside violin concertos and songs. DAMROSCH, Walter Joh. xe.s (1802—). An. iiii(.;ui nuisician, son of Leopold Daui- rosch, born in Breslau, Prussia. He came to the Lnited States, and was made conductor of the Harmonic Society of Newark, N. J., in 1S81, and organist of Plymouth Church, Brookljni, in 188 4. In 1885 he succeeded his father as con- ductor of the Oratorio and Symphony societies, and became assistant conductor of German opera at the iletropolitan Opera House, New York. In 18y4-99 he directed several operatic ventures, at first German, and subscquentl}' French and Italian. In 1900-01 he conducted the German operas at the iletropolitan Opera House. He produced, in 189(3, an opera. The Scarlet Letter, founded on the novel by Hawthorne, composed a Te Deum, in honor of Dewey's victory in Manila Bay, and siiorter pieces and songs. His nuisic is melodious, and the accompaniments to his songs are often striking. DAMS AND RESERVOIRS. A dam is a barrier built across a stream or across a valley or other depression, to raise the level of water or to retain or store water for the supply of cities, towns, or villages, for irrigation, hydraulic mining, power, or manufacturing jjurposes. A reservoir is a basin or other receptacle used for receiving, storing, or distributing water. Reser- voirs are often, but liy no means always, formed by a dam connecting the banks of a stream or the sloping sides of a vallej', canyon, or some more basin-like depression. The terms dams and reservoirs are used in speaking of devices to confine substances other than water; as when clay is used to hold back molten metal of any sort, or as in dentistry, where a dam is built by a dentist to keep saliva out of a cavity, or when a receptacle is attached to a stove, lamp, or ma- chine for heating or storing water, oil, or other liquids, prior to or during use. The dams and reservoirs considered below will be only those constructed to retain water. D.^ilS. Where earth cannot be used, the choice of materials until quite recently has been between timber, timber and loose stone, and masonry. Within recent years a few dams of steel or of steel reinforced by masonry have been erected. Of course the greatest care must be taken to provide against dam failures, for which there are the following cotnmon causes: ( 1) By sliding on the base or on some horizontal joint; (2) by over- turning; (3) by fracture due to tension; (4) by crushing, in the case of masonry dams; (5) by erosion, in the case of earth, or, though rarely, by breaking up and washing away, from the top downward, in the case of masonry structures. After a good site has been chosen and the utmost care devoted to the construction of the founda- tions and the supervision of the material and workmanship, the chief factor of safety in dam construction is obtained by placing a sufficient volume and weight of material in the dam itself to withstand the pressure upon it. Tliis pressure is directly proj)orlioned to the height of water behind the dam and not to the total volume, as is sometimes supposed, in well-designed earth dams the cross-section is so great, for other reasons, as to give a weight far in excess of that which could be removed by the pressure of the retained watef. But in masonry dams the cross- section may be proportioned to resist the pres- sure with mathematical nicety, allowing, of course, the factor of safety common to all good engineering work. In the new lyjie of steed dam.s questions of volume and weiglit yield plac<a to the tensile and compressive strength of the material. A most essential feature in the design of dams of all classes is ample provision for passing waste or flood water. Otherwise the increased, pressure against the up-stream face of the dam due to the excessively high water in the reservoir, or else the force of the current in passing over the top of the dam may cause a serious rupture. In overfall dams relief may be obtained, in some cases, by providing tlood-gates at erne end of the structure, either connected with or detached from the main dam; by having a crest to the whole dam which can be dropped in time of floods (see Movable Dails, below) ; or, in connection with one or both of the foregoing precautions, there may be an artificial overflow or waste channel leading from a spillway above or at one side of the dam down to the natural channel of the stream some distance below. Such a spillway and overflow channel are essential to all earth dams. It should also be noted that waste gates, or under sluices, are sometimes provided beneath the crest of masonry dams, particularly in India. These may be placed near the bottom of the reservoir to permit washing out deposits of silt. Where no other means are feasible, waste water may be carried to a point below the dam through a tunnel cut in the solid rock at one side and beyond the structure itself. Earth Dams are formed by depositing the natural soil from the vicinity of the site in thin layers to form the structure and carefully rolling or otherwise rendering conjpact each layer be- fore another is added. Water is sometimes ap- plied to the earth to help compact it. Soil that will compact readily and be as little porous as possible should be selected, but it is difficult and generally impracticable to make earth dams im- pervious to water. Since continuous percolation through an earth dam would lead to its ruin, it is customary, where an attempt is not made to secure imperviousness through the whole struc- ture, to place a water-tight barrier either on the upper face of the dam or at its centre. The former is known as a lining and the latter as a heart or core wall. Both a lining and a heart- wall may be used. Heart-walls may be com- posed of a carefidly selected mixture of clay and loam or sand, called puddle: of concrete; or of stone masonry plastered with cement. One of the advantages of the heart-wall is that it can be carried well into the bed and hanks of the val- ley, beneath and beyond the main part of the dam, which is a great safeguard against leaks between the natural ground and the artificial structure. Whether or not the upper face of the dam is lined to prevent leakage, it must be paved with stone, concrete, or brick to prevent damage tc the earth slope by the action of the waves at