CANAL, an artificial channel for water, formed for purposes of drainage, irrigation, or navigation, but now usually employed to designate only such cuts as are intended for the passage of vessels.* Canals date from a period long anterior to the Christian era, and were employed as a means of irrigation and communication by Assyrians, Egyptians, and Hindus; also by the Chinese, whose works of this kind are said to be unrivaled in extent; one of them, the Imperial C., having a length of about 1000 miles. For the most part, however, these early canals were of one uniform level, and hence exhibit no great skill or ingenuity; and the moderns were content to follow the rudimentary efforts of the ancients in this way until the 15th c., the invention of the lock (q.v.)—showing how canals might be generally and advantageously used for inland navigation in countries whose surface was irregular—gave a great impulse to this branch of engineer ing. The Italians and Dutch, for both of which nations the invention of the lock has been claimed, were the first to develop this kind of engineering in Europe. In France, the first C., that of De Briare, to form a communication between the Loire and the Seine, was opened in 1642. In 1681 was completed the greatest undertaking of the kind on the continent, the G. of Languedoc, or the C. du Midi, to connect the Atlantic with the Mediterranean. The length of this C. is 148 m., it has more than 100 locks, and about 50 aqueducts, and in its highest part it is no less than 600 ft. above the sea. It is navigable for vessels of upwards of 100 tons. It was not until nearly a century later that C. navigation assumed importance in England, through the sagacity, energy, and liberality of the duke of Bridgewater (q.v.), and his celebrated engineer, James Brindley (q.v.). The success of these works stimulated other public persons to engage in similar undertakings. Speculation in C. shares became a mania similar to that which overtook the people in connection with railways at a more recent period, and a crash ensued on the prospect of war in 1792. It would be an endless task to pursue the his tory of canal development in Britain, which speedily became intersected with these watery highways to an extent unequaled in any European country save Holland. Is
the space at our disposal, we shall briefly consider the several kinds of canal. See SuFA and SUEZ CANAL.
Canals may be divided into three general heads—viz.. 1. Canals proper, Le., entirely artificial channels, having no water running through them beyond what is necessary for their own purpose; 2. Tidal, i.e.. affected by the rise and fall of the tides; and 3. Rivers rendered navigable by weirs built across them to increase their depth, and having a lock at one end for the ascent or descent of vessels; and occasionally, when there is much fall, or any formidable obstruction in the river, by lateral cuts, with locks for part of their course.
Another division may be made (1) of ship-canals for the transit of sea-going vessels generally, from sea to sea; these are necessarily of large dimensions, and must be crossed by swing or draw bridges; and (2) of canals for the passage of mere boats or barges, gen erally without masts, so that they may be crossed by stone or other solid bridges. The largest ship C. in Europe is the Great North Holland C., completed in 1825, which has a breadth of 125 ft. at the water-surface, and of 31 ft. at the bottom, with a depth of 20 feet. It extends from Amsterdam to the Helder, a distance of 51 m. ; it thus enables ships of as much as 1400 tons burden to avoid the shoals of the Zuyder Zee. The sur face of the water in this C. is below the high-water level of the German ocean. from which it is protected by embankments faced with wicker-work. The locks on this C. are 297 ft. long, 51 ft. broad. and 20 ft. deep. There is a similar C. from near Rotterdam to Helvoetsluis, to avoid the shallows of the Brill at the mouth of the Maas. Another great ship C. is the Caledonian 0 (q.v.). The Forth and Clyde C. is also one on a smaller settle for the passage of sea-going vessels. Its length is 35 m. ; its medium width is 56 ft. at the surface, and 27 ft. at the bottom. and its depth 9 feet. It has 39 locks, each 75 ft. long, and 20 ft. wide, and a rise of 155 feet. In constructing ship-canals, it is important to secure a sheltered entrance, one not likely to become silted up, and of sufficient depth to admit vessels at all times of the tide; and towing-paths on both sides are desirable.