Page:The Canal System of England.djvu/48

 On the Manchester Ship Canal and the Weaver, the culvert-openings are distributed along the side walls, but even then, with only a fall of 16 ft., great care is necessary to prevent damage to small craft during the filling of the lock.

The only way of meeting the difficulty of a deficient water supply for the use of the lock, is by pumping. An efficient pump will raise 1,000,000 gallons of water 100 feet for 20/-. Now, assuming for the traffic from South Staffordshire to London, or vice versa, that water had to be raised by pumps to an aggregate height of 900 feet (which would doubtless be more than would be required, the water for the supply at the present time not being raised one quarter of that height, the balance being obtained from gravitation-supplies), this would give an expenditure for pumping water for the whole journey to London of about 4d. per ton, and if double locks were used the cost would be 2d. per ton of cargo, or 3d. per ton of cargo, assuming that half of the boats returned empty.

II. Another method of effecting changes of level is by the use of inclined planes. The most extensive use of planes, is on the Oberland Canal in Germany, where there are five in succession, with lifts varying from 45 to 80 feet. The boats are only of 60 to 70 tons burthen, with flat bottoms, and are not kept afloat, but rest on a grid for nearly their whole length. This system does not appear to be