The Probert Encyclopaedia of Science & Technology

CANAL

A canal is an artificial water-course for the transportation of goods or passengers by boats or ships, or for purposes of drainage or irrigation. The canals most familiar to ordinary readers are for navigation. These consist usually of a number of different sections, each on one level throughout its course, but differing in relative height from the others. From one section to another boats are transferred by means of locks, or it may be by inclines or lifts.

The lock is a water-tight enclosure with gates at either end, constructed between two successive sections of a canal. When a vessel is descending, water is let into the lock until it is on a level with the higher water, and thus permits the vessel to enter; the upper gates are then closed, and by the lower gates being gradually opened, the water in the lock falls to the level of the lower water, and the vessel passes out. In ascending the operation is reversed.

The incline conveys the vessel from one reach to another, generally on a specially-constructed carriage running on rails, by means of drums and cables.

The lift consists of two counterbalancing. troughs, one going up as the other descends, carrying the vessel from the higher to the lower level, or vice versa.

Works of great magnitude in the way of cuttings, embankments, aqueducts, bridges, tunnels, reservoirs for water-supply, etc, are often necessary in constructing canals. Canals have been known from remote times, Egypt being intersected at an early period by canals branching off from the Nile to distant parts of the country, for purposes of irrigation and navigation. Under the Ptolemies, before the Christian era, there existed a canal between the Red Sea and the Nile. In China, also, canals were early made on a very large scale. In Holland, where the country is flat and water abundant, canals were constructed as early as the 12th century. The lock, however, was not invented until the 15th century, both the Dutch and the Italians claiming the honour. Since then Europe has been provided with numerous canals, which being connected usually with navigable rivers, give access by water to most parts of its interior.
Research Canal