DRAINAGE 417 DRAKE 12. Diminishes the effect of drought. By making the season earlier tillage can begin sooner and save moisture from wasting. 13. Healthfulness improved. So well known is this fact that large towns have undertaken the drainage of adjacent swamps to render the region more healthful. Kinds of Draiyis. — Cobble-stone or so- called blind drains are undoubtedly the most ancient covered drains ever made. They are trenches partly filled with boul- ders picked up neai'by and covered over with the earth throTi out. Cobble duct. Two rows of boulders are laid in the bottom of the trench three or four inches apart, a third row is laid be- tween on top, and these are covered with smaller stones and finally covered with the earth thrown out. Brush drains are made by filling a trench with wide bottom full of brush laid in with stem ends downstream, treading them down, covering with sod, leaves or strav, and filling in. They are prone to cave in as the brush settles and decays, and are treacherous to animals. French brush differ from common brush drains in having stakes driven X-wise in the bottom of the trench to raise the brush a few inches. Box drains consist of two boards nailed together forming a V, laid in the bottom of trench with the apex up, and covered; or, of three boards, two set on edge three or four inches apart, with the third nailed across the top, placed in the trench open side down. Plug drains are made by means of a plug, five or six feet long, consisting of four or five sections of wood with uni- form elliptical cross sections, three or four inches in diameter, linked together by a short chain and bar for dra'ing the plug along the trench. Beginning at the upper end of the drain the plug is laid chain end downstream, in the bottom of the trench. A few inches of earth is tamped solidly over the plug; it is then drawn on by means of bar and chain, two-thirds of its length, and cov- ered again, etc. Mole drains are made with a mole plow, an implement constructed to draw an iron plug through the ground about three feet below the sui'face. This plow is usually drawn by a capstan with horses or oxen on the sweep. Tile Dra'.nage. — Drain tiles were in use at a very early date, probably during th*^ Roman period. At first three bricks of com.mon or special shape were used for the conduit, consisting of two set up edgewise a few inches apart, with a third across the top. Later a single brick was molded into the shape of the three as above laid. These were superseded by V-shaped tiles with broad soles on which to rest, and perforations along the back to admit the water. Plain cylindrical tiles are now generally used. Outlets. — One of the weakest parts of a drain is the point of discharge. For this reason it is best not to have a sep- arate outlet for each line of ti^es, but rather to collect all into a system with a single outlet. Minors or Laterals. — The smaller sub- sidiary lines are so called in distinction from the main drain, which follows the lower part of the field and receives *he discharge from the smaller drains. Before construction, a drainage system should be carefully studied, surveyed and mapped out, both for greater accuracy of work and for location of drains after- ward. Steam-power ditchers have been perfected, which have demonstrated their practicability where land is free from ob- structions and the grade fairly even. DRAINAGE TUBES, in surgery, are an important addition to the surgical ap- pliances for which this profession is in- debted to a distinguished French surgeon, M. Chassaignac. They are composed of india-rubber, from one-eighth to three- eighths inch in diameter, perforated with numerous holes, and of various lengths. The;, are especially useful in chronic ab- scesses, but also in large wounds. DRAKE. SIR FRANCIS, an English navigator, born in Tavistock, in Devon- shire, England, in 1539. or according to some authorities in 1545. He served as a sailor in a coasting vessel, and after- ward joined Sir John Hawkins in his last expedition against the Spaniards (1567), losing nearly all he possessed in that unfortunate enterprise. Having gathered a number of adventurers, he fitted out a vessel in which he made two successful cruises to the West Indies in 1570 and 1571. Next year, with two small ships, he again sailed for the Span- ish Main, captured the cities of Nonibre de Dios and Vera Cruz, and took a rich booty which he brought safely home. In 1577 Drake made another expedition to the Spanish Main, having this time com- mand of five ships. On this the most v' famous of his voyages Drake passed the Straits of Magellan, plundered all along the coasts of Chile and Peru, sacked sev- eral ports, and captured a galleon laden with silver, gold, jewels, etc., to the value of perhaps $1,000,000. He then ran N. as far as lat. 48^ N., seeking a passage to the Atlantic, but was compelled to return to Port San Francisco on account of the cold. He then steered for the Moluccas, and hold-
