CANAL. Ancient Egypt was intersected with canals, which were used both for naviga tion and irrigation ; and in China they have been in use from before the Christian rem. The first made in Eprope appears to have been that cut by Xerxes across the low isth mus of Athos. The Romans made canals in Italy and in the Low Countries, about the out lets of the Rhine, and probably also in Britain. In modern Europe canal making commenced in Lombardy between the 11th and 13th cen turies, and in Holland, where they may bo compared for number with the public roads of this country, in the 12th century.
The origin of canal navigation in this country dates from 1755, when an act of par liament was passed for constructing a canal about 11 miles long from the mouth of San key-brook, on the Mersey, to Gerrard's Bridge and St. Helen's. The next works of this kind are noticed under EmounwaTEn, DUKE OF ; and Baranxax.
During the remainder of the 18th and the earlier years of the 19th centuries, the con struction of navigable canals was carried on with vigour, until they were made in England alone to an aggregate length of more than 2200 miles. In conjunction with new canals, many rivers have been artificially rendered navigable, so that it has been asserted that no spot in England, south of Durham, is more than 15 miles distant from water communica tion. The introduction and rapid extension of railways has almost entirely put a stop to the construction of canals, and in several instances canals either have been, pr are about to be, drained and converted into railways; but it is by no means indisputably proved that the newer and more rapid mode of transit can compete with canals in the transit of heavy goods, especially as competition has led to a very great reduction in canal charges, and to improved modes of conducting the carrying trade.
In cutting a canal where the soil consists of sand, gravel, loose rock, Qv other matter through which the water will percolate, the floor and sides of the canal must be covered with en impervious lining, called puddling, which generally consists of light loam and coarse gaud or fine gravel, well mixed with water, and applied, in a serrii-fluid state, in three or more successive strata, each carefully worked into the preceding, to the thickness of about three feet. The puddling is then co vered with common soil to the depth of 16 or 24 inches. Strong clay is pot suitable for puddling, on account of its tendency to shrink and crack, nor is any soil containing roots or other organic matter which would decay and leave cavities. As a further security against the escape of water, mud or puddle-ditches or gutters are sometimes formed along the sides of the canal. They are ditches about three
feet wide, dug perpendicularly to a depth below the bottom of the canal, and gradually filled with puddling stuff to a few inches above the top water-line. When the banks are raised natural level, if the soil be of a porous nature, their stability will be aided by covering them with turf.
Canals are supplied with water from springs and rivulets, and reservoirs are occasionally necessary. Steam-engines may in some cases be indispensable for raising water to supply these reservoirs ; and many arrangements are necessary with the owners of mills and others affected by any interference with the waters from which a supply may be taken. Puddling, embanking, and other engineering operations may be needed in improving the streams adopted as feeders; and in some cases brick culverts or iron pipes may have to be used to conduct the supply. Where the feeders have to be conveyed across a valley or another stream, cast-iron pipes may be found very ad vantageous.
When the canal passes through an uneven country it must frequently he conducted in a very tortuous course to maintain the level ; and deep cuttings, tunnels, embankments and arched or iron aqueducts must be introduced where the level of the canal is unavoidably much below or above the natural surface. Canal tunnels are usually of smaller trans yerse dimensions than those found on rail , ways, though this is not invariably thp case ; but many are of great length. That at worth, on the Grand Junction Canal, is 3080 yards, or a mile and three quarters long ; that on the Thames and Igedsvay Ptnal which has been recently converted into a railway tunnel, is about two miles and one-eighth ; one on the Leominster Canal at pensax is 3850 yards, or nearly two miles and a quarter ; and the Marsden tunnel, on the Huddersfield is 5451 yards, or upwards of three miles long. The tunnels or excavations on the puke of Bridgewater's Canal, which is conduCted by several channels into the heart of a coal mine, are said to be altogether eighteen miles long. Telford introduced, for situations where a canal is greatly elevated above the surface, aqueducts formed of cast-iron plates screwed together by means of flapches, and supported upon piers or pillars of masonry. The first aqueduct of this kind was that for carrying the Shrewsbury Canal across the Fern valley at Long Mill ; but the most extensive and re markable is the Pont-y-gysylte, which carries the Ellesmere and Chester Canal over the.Dee at an elevation of about 125 feet above the bed of the river. The trongh or aqueduct is 988 feet long, 20 feet wide, and 6 feet deep, and it is supported by la pairs of stone pil lars, 52 feet apart.