Drainage by Gravitation. 2 1 



miles distant The total cost of working the boat, for labour, 

 coal, oil, Sec, was 65/., equal to about ys, 6d, per chain. It 

 was estimated by Mr. Harrison, the surveyor of the district, 

 that to have done this work by spade labour would have cost 

 200/. 



In the river Welland, by the aid of this machine, a length 

 of 24 chains was deepened 2 feet for a width of 17 feet in 

 three days* working. In the river Glen the channel was 

 deepened 3 feet 6 inches, with a very slow current running, 

 the soil being stiff clay. 



Sevao. appliances L breaking „p shoals and loosening the 

 bed of streams have been brought out and used at different 

 times, both in this country and abroad. 



In the river Stour a boat was used, fitted with a kind of 

 rake at the bow, adjustable to the depth required. At the side 

 of the boat wings were fixed which could be extended so as to 

 form a temporary dam when the rake was lowered. This dam 

 caused the water to rise on the upper side. As soon as a head 

 of from six inches to a foot had accumulated, the pressure 

 forced the machine forward, dragging the rake along the 

 bottom. The rate of progress was about three miles an hour. 

 The machine is said to have been very effective in scouring 

 the river.* 



In removing the shoals in the river Maas a boat was used, 

 fitted on each side with a screw propeller, 3 feet 6 inches in 

 diameter, which could be raised or lowered by gearing on the 

 deck. The screws were adjusted so as nearly to touch the 

 shoals, and as the boat moved, these were caused to revolve 

 at the rate of 150 revolutions per minute, by bevel gearing, 

 driven from a cross-shaft by belting from the fly-wheel of a 

 portable 12 horse-power engine. By the aid of this machine, 

 shoals consisting of sand, clay, and peat, were easily and 

 quickly moved, sand at the rate of 130 cubic yards an hour, 

 clay and sand mixed, 116 yards. The boat was moved to 



* Trans. Inst. C. E., vol. ii. 



