A gate consists of two leaves, the swinging edges of which meet on the centre line of the chamber, but as each leaf is somewhat than half the width of the chamber, they do not form a straight diaphragm across the chamber when closed, but are shaped like a very flat letter V with its point projecting toward the upper level or reach. This construction gives greater strength to resist the pressure of the water. The height between the bottom of the down reach and the bottom of the upper reach is called the lift of the lock. The practicable height of lift in lock construction is limited, and where great differences in level have to be over come, a series or flight of locks built end to end is employed. The dimensions and main structu ral features of the locks of several canals are given in succeeding sections.
Where a vessel passes through a lock from one level to another, a loekful of water is lost from the upper level to the lower level for each pair of boats passed. Where water is scarce and the total lift is large. therefore, resort is some times. had to inclined planes up and down whieh the boats are transported in cradles or tanks running on wheels and hauled by cables or other power. Inclined plallcs for canals are of Very early origin, being at one time quite extensively used, and some of these old inclines are de scribed in the following section. A more im portant. system of transferring canal-boats from one level to another is the vertical lift or lift lock system. which has been installed in a num
ber of places and is proposed for several other places where very high and important differences of level °cern% In the vertical lift-lock system, the boat is floated into a movable trough, the ends of which are closed by gates, similar gates close the ends of the eanal approaches. When the gates are closed behind the boat (lie trough is raised or lowered, as the ease may be, until it coincides with the other level of the canal, when the front gates are opened and the boat proceed, upon its way. The trough is raised and lowered by means of hydraulic or other power aided sometimes by counterweights or flotation tanks. The first vertical lift on a large scale was that built at Andertom Emdand. in 1875: a seemid was built at Les Fontinettes, France, in ISS5: a third at La Bel gium. in 1888; and a fourth at rfeinriehenberg, G'ermanv. in 1895. In 1895 a lift lock was de signed to replace the flight of locks at Lockport, N. Y., on the Erie Canal. A summary of the essential details of the Ande•ton, Les Fonti nettes, La Louviere, and Lockport lifts is given in the accompanying table: miles long. connecting Stockholm and Gothe• burg. in Sweden, was completed in 1832; and the Danube-..\ lain Canal, 108 miles long, was constructed 1836-46. France, however, was the The Heinrichenberg lift lock has a tank 229.6 X 28.2 X 8.2 feet, with a lift of 52.45 feet.