DAMS AND BESERVOIKS. r64 DANA. ing the sites, the construction of impounding reservoirs pertains mostly to the dam and its accessories. One additional element of impor- tance in some cases is the excavation at the border of reservoirs to prevent shallow flow- age and the growth and decay of vegetable mat- ter which would occur when these slopes are alternately exposed and covered by the varying levels of water in the reservoir. Settlixg Reservoirs, also known as subsid- ing and as sedimentation reservoirs, are shallow basins, with long weirs between the several compartments over which the water flows in thin sheets, thus drawing olT only the upper and most clarified layer. (See Water Pi"Rific.- TIO^'. ) It is desirable to make provision for re- moving the mud, to which end the paved bot- toms may slope to a common point and then connect with a scour-pipe, through which the mvid may be flushed with a stream of water from a hose. Distributing Reservoirs are generally located within or near the city which they serve. They are often classified as high, low. and middle service, according to their elevation and the areas which they supply. They may afTord stor- age for periods ranging from a day or two up to several weeks; but in tlie latter case they would perform the duty of a storage reservoir as well. Occasionally distributing reservoirs are formed by a dam across a stream : but as a rule they have masonry walls above or below the natural surface. The construction of embankments or walls does not difl"er essentially from that of earth and masonry dams, except that when masonry is used the principles of design are more like those involved in the planning of earth retaining w'alls, subjected, of course, to water pressure on the other side at times: but also liable to be empty. It is common to line the inner slopes of reservoir embankments with stone, brick, concrete, or asphalt. The bottoms are frequently lined like the sides. When concrete is used it is well to lay it in relatively small squares, with a good filling for the joints, to prevent cracking. Covered Reservoir.s may have vaulted roofs of masonry, generally cither brick or concrete, or else less expcnsic and more temporary roofs of timber, !Much ingenuity has been exercised to find a cheap and permanent covering, since the work at best adds largely to the cost of the structure. In fact, the cost is so great that cover- ing is rarely attempted in the United States, except for relatively small reservoirs receiving either filtered water or that from underground sources, either of which is liable to injury through the development of organisms giving rise, in their life processes, to bad ta.stes and odors. Bibliography. Wegmann, Design and Con- struction of Dams Ofcw York, 1899) ; Schuyler, .Reservoirs for Irrigation. JVater Power and Do- mestic ffiipphj (New York, 1901) : Frizzell, ^'ater Power (New York, 1901) : also general treatises on water-works by Fanning, Folwell, Ooodell, and Turneaure. and Wilson, Manual of Irrigation Engineering (New York, 1897), DAMSEL FLY (so called from the French name demoiselle). An insect of the family Agrionidtp, order Odonata, closely allied to the dragon-flies. They are, says Heward. the small, graceful species, with extremely slender bodies and narrow, clear wings, held vertically in re- pose, which are very commonly found over large bodies of still, fresh water. "All of our North American species [about 75] are snuill. but in tropical regions they grow to a large size, and some South American forms are among the larg- est species of the order Odonata, They do not lly high in the air, but frequent low-growing aquatic vegetation. The colors as a rule are rather dull, but the slender bodies of some are brilliantly blue, green, or even red." Many authors unite with these as a subfamily the dark-colored, prominent-eyed flies otherwise re- garded as constituting the separate family CalopterygidiP. The life history of these flies is substantially that of the dragon-flies (q.v.). See Plate of Dbagox-Flies. DAMSEL OF BRIT'TANY. A title given to Elcan(U- of Brittany, sister of Arthur, Count of Brittany, and niece of King John of England, who confined her in the Castle of Bristol, where she died in 1241, DAN (Heb., judge). A city on the northern boundary of Israel, called originally Laish (Judges xviii. 29), but renamed Dan by the Danile invaders. Owing to its northerly loca- tion (Gen. xiv. 14), it was often used in con ncction with Beersheba (I. Sam. iii. 20: II, Sam, iii, 10) in the phrase "from Dan to Beer- sheba," to express the whole land of Israel, The Danites introduced an idolatrous worship (■ludges xviii.), but this gave way to the calf- worship introduced by Jeroboam ( I. Kings xii. 29). -At the solicitation of Asa, King of Judah. Ben Hadad, the Syrian King, invaded Israel, and, among other cities, Dan was destroyed (I, Kings XV. 20: 11. Chron. xvi. 4). The ruins of the city are identified with modern Tel-el-Kadi. DAN. The eponymous ancestor of the tribe of Dan, the son of .Jacob and his concubine Bilhah (Gen, .xx, 5, 6). The tribe was one of the smallest and weakest of the Helirew con- federacy. Belonging to the northern group, its territory lay southwest of Ephraim, occupying the valleys of Sorek and Ajalon (Joshua xix. 40-40). Owing, however, to difficulties with the Amorites (.Judges i. 34), we find them later migrating to the far north, and conquering the^city of Laish, which they rebuilt and called Dan (.Joshua xix. 47: Judges xviii.). Samson (q.v.) was of the tribe of Dan (.Judges xiii. 2, 24, 25), The earliest reference to the tribe is in the song of Deborah (.Judges v.) : the passage in which Dan is reproached for seeking protection in ships, instead of coming forward to lielp its brother tribe Bilhah, is obscure: but it seems certain that at this period already Dan's settle- ments were to the north and near the seacoast, Dan, though designated as a 'concubine' tribe, which generally indicates secondary rank, plays no unimportant part in the early traditions and legends. This is in part due to the fame and antiquity of the .sanctuary at Dan, which as late as the days of Amos is put on a level with Bethel and Beersheba (Amos viii, 14), In this sanctuary the older rites and practices were preserved with great fidelity, and its priests traced their origin to Hoses himself (.Judges xviii. ,30). The name Dan ('judge') may orig- inally have been the title of a deity. DA'NA, Charles Anderson (1819-97). An .merican journalist, born at Hinsdale, N. H,,
