tion, as in the butterfly, would probably present the form found by engineers to be that of the beam of greatest strength and lightness, viz.: the greatest amount of material thrown into the oval flanges, connected by the thinnest possible median support. According to Drury, these insects are 2 years in reaching the perfect form from the egg; after flying about a few weeks, and having performed the act of reproduction, the wings become ragged, the strength fails, and they soon die. They are sometimes seen in immense swarms; M. Poey says that at certain seasons of the year the north winds sweep hosts of them into the neighborhood of Havana; in Belgium in 1854 a swarm was seen extending of a mile, and requiring nearly an hour to pass a given spot, the lowest individuals flying at a height of about 6 feet. The restricted 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, of a rough appearance, and a dirty color; they have 5 appendages to the tail. The genus ashna (Fab.) includes the large species, with long slender bodies, which keep the wings expanded when at rest; the larvæ are larger, long and slender, with the abdomen flat below and rounded above; this includes the L. grandis (Linn.), the largest and most predaceous of the British genera; there are about a dozen species in Massachusetts. In the genus agrion (Fab.) the wings are perpendicular during repose, the head transversal, and the eyes far apart; this includes the species with the slender and filiform abdomen, sometimes of extraordinary length; the larvae are small, with round slender bodies terminating in 3 feathery appendages; there are about 10 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. See BALSAMS. DRAGOONS (Fr. dragons, from Lat. draconarius, a standard bearer), a species of cavalry first introduced by Marshal de Brissac in France in the 16th century, when they were armed with muskets and trained to fight according to circumstances, either as cavalry or infantry. They manoeuvred either in or out of the line, extended themselves as skirmishers on the wings, fired upon the enemy, and then deployed behind a column of infantry to reload their pieces, promptly returning again upon their adversaries. They were subsequently of especial service in passing rivers and defiles, and as an escort for the baggage and convoys of artillery. In the 18th century they lost their hybrid character, were generally used as cavalry, and now form in most of the European armies a grade between cuirassiers and hussars, mounted on horses too heavy for the latter and too light for the former. Nicholas of Russia created a dragoon corps of 8 regiments designed to act either as cavalry or in

fantry, but they were reduced to simple cavalry by his successor. The first corps of dragoons in England, called the royal regiment of dragoons of North Britain, was raised in 1681, and is now the Scots greys. There are two regiments of dragoons in the U. S. army. (See also CAVALRY.)

. DRAGUIGNAN, a town of France, capital of the department of Var, 41 m. N. E. from Toulon; pop. in 1856, 9,900. It rises in the midst of a fertile valley, surrounded by high hills covered with rich vineyards. It is well built, with several elegant edifices, and numerous fountains. It contains a library of 15,000 volumes, among which are a few very valuable works, a cabinet. of medals and of natural history, law courts, a parish church, and a fine clock tower. The inhabitants are employed chiefly in the silk mills and soap works of the environs, and in prepar ing and selling olive oil. Draguignan is an ancient town; was last fortified in 1615; and its possession was a matter of contention in many of the wars of France.

DRAINAGE, the art of freeing land from superfluous water by causing it to flow off in channels or through porous substances. The system of drainage adopted for cities and towns is commonly described as SEWERAGE, and will be noticed under this head, as that of mines in the article devoted to that subject. (See also PUMP.) The art is of especial interest in its application to the reclaiming of wet lands, and the improvement of those through which the water that falls upon them in rain, or is brought by subterranean channels, does not find a ready exit. The importance of this branch of the art appears to have been appreciated by the ancient Romans, who are known to have constructed open drains for conveying away the superficial water from their lands, and to have laid underground water pipes of earthenware, which some suppose were for the same purpose, but which are with more probability referred by others to the purposes of aqueducts for supplying water to their houses. 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. In this work the tendency of wet lands to produce the flag and rush instead of useful crops was forcibly portrayed, and the remedy of deep drainage as strongly urged. 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 regarded as the source of the "corruption that feeds and nourisheth the rush or flagg," even to the depth of 3 or 4 feet, and the filling in of the trenches with stones, or with faggots covered over with turf. It was long, however, after his time before the excellence of this system was generally recognized, and little attention appears to have been directed to the subject until the latter part of the next century. About the year 1764 a shrewd farmer of Warwickshire, Mr. Elkington, undertook to investigate the peculiar qualities

of one of his fields in which the sheep were badly affected by the rot. He discovered that when an impervious stratum beneath the soil was perforated with an iron bar, the water confined below welled up and flowed away; and he hence inferred that the water in wet lands came chiefly from subterranean sources, and might be removed by tapping the stratum that confined it, and thus letting off the superfluous quantity. On this theory he established an original system of drainage, and was himself remarkably successful in seeking out the sources of the water, the supplies of which, after reaching by an auger, he drew off in a single deep channel dug for the purpose. 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 Mr. James Smith of Deanston, first brought forward in 1823. This, which its inventor called frequent or thorough drainage, and others named the Deanston system, was contrived with reference to the removal of the water collected by rains upon the surface, as well as that lying beneath the soil, and was in fact the practice recommended nearly 200 years before by Capt. Blyth. A series of parallel drains were sunk in the direction of most rapid descent, and being partially filled with stones small enough to pass through a 3-inch ring, were covered over with soil. At the bottom a main drain was constructed, of sufficient capacity to convey away all the water from the smaller drains, and this he directed should be made in stone work or with tiles. The new practice met with great opposition from the advocates of the method of Elkington, but finally came to be regarded as the only complete system applicable in all cases. In some instances the other plan may no doubt be economically adopted. The drains came at last to be made chiefly of tiles, for the manufacture of which the first machine was invented by the marquis of Tweeddale. The practice has been successfully introduced into the United States; and in Albany and New York draining tiles are already a considerable branch of manufacture. They are also made in New Jersey, Pennsylvania, and Ohio. Their forms and the manner in which they are used will be described after a few remarks upon the necessity and effects of drainage.—Wet lands are well known to be unfavorable to the production of large crops; it is also true that grains, potatoes, grass, &c., are of sounder and better quality when grown upon lands not subject to excess of moisture. The soils that retain it are correctly described as cold, while the more porous soils of a sandy nature are called warm. The former are chilled by the evaporation continually going on, while the latter are warmed below by the rain water which percolates through from the surface, and are heated by the direct action of the sun's rays. By the experiments of Mr. Parkes in a bog in Lancashire, it appears that by giving free passage to the water through a cold soil by thorough drainage, its temperature at the

depth of 7 inches may be raised 10° above that of undrained adjoining land of the same quality. Thus drainage produces the effect of a warmer climate, and may add in fact many days to the length of the season; and this not merely by reason of the warmth extended for a longer period, but in the spring the soil is sooner prepared for cultivation, and may be in condition for ploughing and planting even two weeks before neighboring land of similar quality in other respects would admit of the passage of oxen and horses for working. An instance of such a gain in time was reported in 1856 by the secretary of the board of agriculture of the state of Maine. In the late spring of the northern states, where the snow often lies in April, and the ground is saturated with moisture in May, the advantage thus secured is of great importance. While frequent accession of water is a great benefit to lands through which it finds a ready passage, its retention impairs in various ways the fertility of the soil. It prevents the pulverization of the earth by the plough and harrow, and the circulation of air to the roots of the plants. It nourishes a growth of noxious plants, and in woodlands its injurious effect is seen in the production of many lichens, fungi, and other parasites upon the trees. Even the cattle and sheep pastured upon wet lands are subject to diseases from which those in dry fields are comparatively free, and are moreover pestered by swarms of flies and mosquitoes, which disappear as the same lands are drained. Man himself is often the greatest sufferer from undrained lands, which tend to engender fevers and agues; and these are known to prevail long after the forests have been removed, showing that the cause is not so much the decay of large bodies of vegetable matter, as the cold dampness produced by the saturation of the earth with moisture. By the recent researches of Dr. H. I. Bowditch of Boston, it appears that consumption also is more prevalent in those localities in Massachusetts which are badly drained, 50 out of 55 districts in the state of decidedly consumptive character being found wet by contiguity to ponds or marshes, or by reason of low and springy lands. In the vicinity of the wet and unhealthy localities are often found others which appear to be as free from any tendency to induce or aggravate the disease as the distant regions to which patients are sent for recovery. It is a singular fact, fully established by experience, that undrained lands are more liable to suffer from drought than those thoroughly drained. The former in a dry time become baked and compact, and do not readily absorb moisture from the atmosphere; but a well pulverized and open soil receives into its pores and absorbs like a sponge the dew and aqueous vapor in the air. The moisture finds its way to the lower portions of the soil, and is there taken up by the rootlets, which penetrate deep into the loosened materials. Deep or subsoil ploughing is thus seen to be most advantageously employed in connection with underdraining. The same cause which prevents the

penetration of the water also keeps near the surface the fertilizing substances applied as manure; and these exposed to the heat of the sun are in great part dissipated, their richest ammoniacal portions going off in exhalations to be precipitated by the rains upon other lands. Undrained soils in cold climates suffer from another cause. They are liable to freeze when saturated with moisture; and as they thaw, or, in popular language, as the frost comes out of the ground, they are so heaved and broken up, that the roots of the grasses and winter grains are thrown out, and the plants are destroyed; this is what is called winter-killed. By draining and subsoiling, a way is opened for the moisture to sink beyond the reach of frost, and the soil is left too dry to be disturbed by the thaws of spring. From these remarks may be inferred the inutility of mere surface draining. Open trenches may convey away the surface water, but do not reach the cold stagnating repositories beneath the soil, which check that free circulation of fluids which is as essential to the health of vegetable bodies as that of the air to animals. Such ditches should be used only as brooks in the lowest grounds to convey away the water discharged into them by the underground drains coming down the slopes. Deep ditches partially filled with small stones or with brush, or laid at bottom with flat stones, are found by long experience to be not so well adapted to accomplish the object sought for as drains laid with tiles. These are short pipes moulded and baked of brick clay. Some are of cylindrical shape; and in others, called the horse-shoe tile, the section is an incomplete circle, and when laid the tiles are placed upon the 2 edges, either directly upon the ground, or separated from it by the intervention of flat pieces of the same material, placed so as to break joints with the tiles. In another form which is very generally used, called the sole tile, the flat bottom piece, instead of being separate, is a part of the tile itself, and is the foot upon which it stands. This and the pipe tile are considered far superior to the horse-shoe. Tiles are made of various sizes from 2 to 8 inches diameter, moulded by machines in lengths of about a foot, and baked as thoroughly as common hard-burned bricks. They are carefully set in the ground end to end; but the cylindrical pipes are often furnished with a collar which slips over and holds 2 adjoining ends. The bottom of the trench is dug with excavating tools, made for the purpose, just wide enough to admit the tiles. The water filtering through the soil passes into the pipes by the numerous joints, entering chiefly at the bottom, and the multiplication of these joints is the chief object of the short lengths. Tiles should always be imbedded in compact soil, and at a depth somewhat dependent upon the contour of the ground as well as other circumstances. A sufficient slope must be secured for the water to flow readily through the drains. There should be no interruptions to the descent,

causing depressions in which sediment might ac cumulate to obstruct the drainage. The least fall admitted by most authorities in the usual sized drains is not less than 1 in 600 or 700; but so gentle a slope is rarely advisable; indeed, not less than 1 in 200. The depth_generally agreed upon as the best is at least 4 feet. The tiles are at this depth rarely reached by a hard frost, and are not disturbed by the pressure of the subsoil plough, which penetrates a few inches over 2 feet below the surface. This depth is also lower than the roots of most of the crops are likely to extend; but the tiles cannot be placed beyond the possibility of injury from the roots of willows, poplars, and other trees which strike down in an open soil to uncertain depths. Their distance apart should depend upon the nature of the soil. In compact clays they have been set within 15 feet of each other; but this is unnecessarily close. If the subsoil be clayey, it is not well to exceed 30 feet; for if the drains once laid are found to be ineffectual, as they have in many instances proved, the only expedient is to make an additional one between each 2 of the original set. If the subsoil is very porous, the tiles may be placed 40 feet apart; but if trials at a greater distance than this are ever found effectual, it is believed their success should be referred to the principle of Elkington, the drains tapping a porous stratum containing water which was kept from flowing by an impervious overlying stratum. The effect of drains is not always perceived immediately after heavy rains. Some time is required for a dry soil to become saturated, and the moisture is then gradually given off below. The plants thus have sufficient opportunity to obtain the benefit of the water which passes through, and no danger is incurred of overdrainage, especially as the lands are left in better condition, as already stated, for absorbing atmospheric vapor. In stiff clayey soils the operation, though it would at first appear impracticable, is greatly facilitated by the property of the clays to shrink and open in cracks in passing from a wet to a dry state. This process commences near the drains, and the cracks extend back, serving as they open as minor channels for leading the water down to the tile beds. They have been traced stretching across through the clay with innumerable ramifications nearly from one drain to the next; and though they close again when very wet, they still let water pass along their lines.— The most extensive agricultural drainage operations in the United States are on the farm of Mr. John Johnston, near Geneva, N. Y. By steadily pursuing the practice for about 20 years, he has accomplished the laying of 210,000 tiles, or over 47 m. An instance of their beneficial effect was observed a few years since, when by the destructive action of the midge the crop of wheat upon 6 adjoining farms was reduced to 7 bushels per acre, while he obtained 29 bushels. The system of drainage adopted in the central park of New York city, under the direction of George E. Waring, Esq., is very complete, and

paid by the proceeds of the sale of the lands, the greater part of which had then been disposed of. The swamp lands and salt water marshes of the United States present vast and almost untouched fields for this system of operations. The accumulations of vegetable matters they contain give fertility to the soil, when the stagnating waters are removed; and the success that has attended small operations undertaken to bring them into cultivation, gives encouragement to expect great results from operations undertaken upon a larger scale. The subject of drainage may be further studied in the number of Weale's "Rudimentary Series," by G. D. Dempsy, "On the Drainage of Districts and Lands." It is also treated in an article in the U. S. patent office "Agricultural Report" for 1856; and by H. Colman in his reports of European agriculture. The very complete treatise of James Donald has been recently republished in New York; and William McCammon, civil engineer of the "Albany tile works," has presented in an advertising pamphlet a summary of the principles and advantages of drainage, with exact descriptions of the tools and methods employed and estimates of cost.

DRAKE, DANIEL, an American physician, born in Plainfield, N. J., Oct. 20, 1785, died in Cincinnati, O., Nov. 5, 1852. His father, a farmer in indigent circumstances, emigrated from New Jersey to Mason co., Ky., in 1788, where Daniel's childhood and youth, up to his 16th year, were passed on a small farm, amid the labors and privations of a frontier life. In Dec. 1800, with only such education as he had received in the course of some 6 months' desultory attendance at different times upon country schools, taught by wandering and ignorant schoolmasters, he was placed under the care of Dr. William Goforth, of Cincinnati, as a student of medicine, and in 1804 he commenced the practice of that profession. In 1816 he was graduated at the university of Pennsylvania, and in 1817 he was invited to a professorship in the Transylvania medical school at Lexington, Ky., in which he lectured one session. In Dec. 1818, on his personal application, the legislature of Ohio granted a charter for the medical college of Ohio, at Cincinnati, and also established there the commercial hospital. In the autumn of 1820 the former institution was opened for students, and for 2 sessions Dr. Drake was connected with it. In 1823 he again accepted a chair in the Transylvania school; and thenceforth, till the close of his career, was with brief intermissions connected with medical schools, holding professorships in that institution, and in the Jefferson medical college, Philadelphia, in the Cincinnati medical college, in the university of Louisville, and finally, again, in the medical college of Ohio, with which he was connected at the time of his death. As a professor of the theory and practice of medieine he held an eminent position, and as a practitioner his reputation was coextensive with the Mississippi valley. His writings were voluminous, but principally of a character

not calculated or intended for permanent use. His first book, the "Picture of Cincinnati" (1815), attained in its day a wide reputation, and drew from Thomas Jefferson a highly complimentary letter. His last work, upon which his fame as an author must principally rest, was "A Systematic Treatise, historical, etiological, and practical, on the Principal Diseases of the Interior Valley of North America, as they appear in the Caucasian, African, Indian, and Esquimaux Varieties of its Population," vol. i. of which was published in 1850, and vol. ii., posthumously edited, in 1854. A memoir of his life and services, by Edward D. Mansfield, LL.D., was published in Cincinnati in 1855.

DRAKE, SIR FRANCIS, an English navigator, born near Tavistock, in Devonshire, according to some authorities in 1539, and to others in 1545 or 1546, died Dec. 27, 1595. His father, a poor yeoman, and a recent convert to the Protestant faith, obtained from Queen Elizabeth an appointment as naval chaplain. He had 12 sons, of whom Francis, the eldest, received a scanty education through the liberality of his kinsman John, afterward Admiral Sir John Hawkins, and as soon as he was old enough to serve as a cabin boy, was apprenticed to the master of a bark. By his industry and frank and decided character he so gained the affections of his master, that the latter at his death bequeathed his vessel to his young apprentice. Being thus at the age of 18 years a good sailor and the proprietor of a ship, he quickly completed his education by learning how to command, and made a commercial voyage to the bay of Biscay and afterward to the coast of Guinea. Inspired by the adventures and successes which the new world then offered, he sold his vessel and invested the proceeds with all his savings in the expedition of Capt. Hawkins to Mexico in 1567, receiving the command of the Judith. The fleet was attacked by the Spaniards, and only 2 of the 6 ships escaped. Drake, barely succeeding in sav ing his own vessel, returned to England, with a loss of his entire property, and fruitlessly petitioned the court of Spain to restore what its subjects had taken from him. Then with an oath he declared that he would obtain by force the rights which he could not get otherwise, and began to sail with the avowed object of pillaging the Spaniards. In 1570 he obtained a commission from Queen Elizabeth. In 1572 he armed 2 ships at Plymouth, with which, joined by a third at Port Pheasant, on the coast of South America, he made a descent upon New Granada, captured and plundered vari ous Spanish settlements, and made at the expense of his enemies a fortune vastly larger than they had taken from him. He returned to England in 1573, and was welcomed as a hero. While at Darien he had seen from a mountain top the waves of the Pacific, and had there conceived the purpose of an expedition into those waters, yet unexplored by English vessels, which he now prepared to execute. His eloquence was sufficent to gain the patronage