Page:The American Cyclopædia (1879) Volume VI.djvu/248

 240 DRAGON'S BLOOD DRAINAGE weeks, and having performed the act of repro- duction, the wings become ragged, the strength fails, and they soon die. M. Poey says that at certain seasons the north winds sweep hosts of them into the neighborhood of Havana ; in Helgium in 1854 a swarm was seen extending three quarters of a mile, the lowest individuals Hying at a height of about six feet. The re- stricted genus libellula, of which nearly 20 species inhabit New England, has a flattened, moderately long body, an almost globular head, the eyes contiguous or approximate, and the wings horizontal when at rest. The larvae are short and thick, rough and of a dirty color; they have five appendages to the tail. The genus ceskna (Fab.) includes the large species, with long slender bodies, which keep the wings expanded when at rest ; the larvae are larger, long and slender, with the abdomen flat below and rounded above ; this includes the L. grandis (Linn.), the larg- est and most predaceous of the British gen- era ; there are about a dozen species in Massa- chusetts. In the genus agrion (Fab.) the Agrion. wings are perpendicular during repose, the head transversal, and the eyes far apart; this in- cludes the species with the slender and filiform abdomen, sometimes of extraordinary length ; the larvfB are small, with round slender bodies terminating in three feathery appendages; there are about ten northern species well known, many of them delicate and beautiful ; among the foreign species are some of the most brilliant of insects. Many of the finest American species of this family are described and figured by Drury. DRAGON'S BLOOD, a resinous substance ob- tained from the fruits of several small palms .Jn the East Indies, from the trunk of drachma draco, a large tree growing in the Canary Islands and Azores, and from p terocarp us draco, a tree of the West Indies and South America. It occurs in oval masses, sticks, and disks. It is inodorous and tasteless, insoluble in water, but soluble in alcohol, ether, and the volatile and fixed oils, with which it forms red solu- tions. It was formerly employed in medicine as an astringent, but is nearly or quite inert. It is sometimes used to impart color to plasters, but is valued chiefly as an ingredient of paints and varnishes. DRAGUIGNAN, a town of France, capital of the department of Var, 41 m. N. E. of Toulon ; pop. in 1869, 9,819. It lies in a fertile valley, surrounded by high hills covered with rich vineyards, and is well built, with several elegant edifices and numerous fountains. It contains a library of about 20,000 volumes, a cabinet of medals and of natural history, law courts, a bo- tanic garden, a communal college, and a fine clock tower. The inhabitants are employed chiefly in the silk mills and soap works of the environs, and in preparing and selling olive oil. Draguignan was founded in the 5th century. It suffered greatly in the religious wars of the 16th and 17th centuries. DRAINAGE, the art of freeing land from su- perfluous water by causing it to flow off in channels or through porous substances. The system of drainage adopted for cities and towns will be treated in the article SEWERAGE. The art is of especial interest in its application to the reclaiming of wet lands, and the im- provement of those through which water does not find a ready exit. The ancient Romans constructed open drains for conveying the su- perficial water from their lands. In England, public attention was directed to the injurious effects of water retained in cultivated lands by the treatise of Capt. Walter Blyth in 1652. The author condemned the shallow open drains in common use, and recommended straight trenches reaching below the spring of "cold, spewing, moyst water," which he re- garded as the source of the " corruption that feeds and nourisheth the rush or flagg," even to the depth of three or four feet, and the filling in of the trenches with stones, or fagots cov- ered with turf. It was long before the excel- lence of this system was generally recognized, and little attention appears to have been di- rected to it until the latter part of the next century. About the year 1764 a farmer of Warwickshire, Mr. Elkington, discovered that when an impervious stratum beneath the soil was perforated, the water welled up and flowed away ; and he hence inferred that the water in wet lands came chiefly from subter- ranean sources, and might be removed by tap- ping the stratum that confined it. On this theory he established an original system of drainage, and was remarkably successful in seeking out the sources of the water, which, after reaching by an auger, he drew off in a single deep channel. This system came into extensive practice in England and Scotland, and its imperfections were not fully appreciated till after the introduction of the system of James Smith of Deanston, in 1823. This was contrived with reference to the removal of the water on the surface, as well as that beneath the soil, and was in fact the practice recom- mended nearly 200 years before by Capt. Blyth. A series of parallel drains were sunk in the direction of most rapid descent, and, being par-