OF THE TYNE AND NEIGHBOURING DISTRICTS. 155 



are exclusive of the interest upon the outlay of capital. Before the in- 

 troduction of hydraulic machinery at these docks, the cost of loading 

 coals by hand amounted to between 5d. and 7d. per ton. 



In point of despatch the hydraulic is equal with the gravitation 

 system, both being limited by the labour of trimming the coal in the 

 hold of the vessel. 



The most remarkable application of a hydraulic machine for loading 

 coals is the one now constructing at Goole Docks, in connection 

 with the system adopted by Mr. Bartholomew for the coal traffic upon 

 the Aire and Calder Canal. The barges, carrying 33 tons of coal each, 

 will be lifted by this machine out of the water, and their contents tilted 

 directly into the hold of the vessel to be laden. 



Becent improvements in the construction of rotatory engines 

 have so simplified and condensed their form, that the application of this 

 class of engines to all kinds of purposes is rapidly extending. A 

 seven-horse power hydraulic engine, worked from the ordinary high 

 (accumulator) pressure, occupies a space of two and a quarter feet square 

 by nine inches deep. Such engines are now being applied directly to 

 new, as well as to the existing, dock gate crabs at the Liverpool 

 Docks, without at all disturbing the present arrangement of the 

 hand power gear of these crabs, which can thus still be used 

 by hand in cases of emergency. Other engines are similarly applied 

 directly to the crabs of hand-power cranes, swing bridges, and 

 other hauling appliances ; to capstans, machines for planing armour 

 plates, &c. The latest improvements in hydraulic engines consists in 

 making them with variable power, so that their consumption of water 

 may be the better proportioned to meet any fluctuations in the amount 

 of work to be done. An engine of this description, capable of being 

 worked up to seventeen horse power, under an ordinary accumula- 

 tor pressure of 700 lbs. per square inch, was exbibited in the col- 

 lection of models at the British Association meeting. 



The advantage of the system of storing up pressure in accumulators, 

 so that a great force can be quickly brought to bear upon heavy masses, 

 . to be rapidly moved for limited distances, is well exemplified in 

 its application to moveable bridges, and the importance is the 

 more felt, in situations where traffic would be seriously impeded 

 by slow action, as, for instance, at the part of the Swansea and 

 Neath Railway, where the line crosses the mouth of the river, 

 and the entrance to the dock in Swansea. The communication 

 of the line is kept up over these two points, by hydraulic draw- 

 bridges. The time occupied in lifting and drawing back the largest 

 bridge — which has a space of 75 feet and weighs 260 tons — is under 1| 

 minutes. At Wisbeach, where the plan of storing up pressure in an 

 accumulator by hand pumps, is resorted to, a bridge weighing 450 tons, 

 can be opened or closed in less than two minutes. 



In noticing the application of water pressurej derived from natural 



