HYDRAULIC POWER APPLIED TO BRIDGES.

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which pillar tlie working valve is fixed, the water enteringand escaping througli the pivot as showu by fig. 2.

A form of Station crane is shown by Plate 23, which repre-sents one of the cranes erected at the new goods Station ofthe North-Eastern Eailway at Hewcastle-on-Tyne. These typesof cranes were explained by Sir William Armstrong in a paperread at the Institution of Civil Engineers .

Plate 24 shows an Elswick “ Moveable Hydraulic Crane.”

When the load to be raised becomes very great (100 tons orso), it is better to substitute some other arrangement for thatof chains. In the case of a large crane which Sir William Armstrong , Mitchell, & Co. erected at the Royal ItalianArsenal at Spezzia, the lift is pei’formed by the direct actionof a piston contained in an inverted cylinder suspended ingimbals from the head of the jib, as shown by Plate 25.This crane is capable of lifting 160 tons through a ränge of 40feet. It is carried upon a ring of live rollers supported by apedestal of masonry, and the slewing is effected by a hydraulicengine applied to a pinion gearing into a circular rack. Thejib projects 60 feet from the centre of rotation, and its heightabove the quay level is 105 feet. If the crane is used to liftmuch lighter loads than the maximum, a chain is employed,which is raised and lowered from a cupped drum, worked bythe slewing engine.

HYDRAULIC POWER APPLIED TO BRIDGES.

The first application of hydraulic power to bridges was in1852, when the Eorest of Dean Railway Company constructeda hydraulic swing bridge over the river Severn . A double leafswing bridge of timber was constructed and worked by hydraulicpower about the same time at the Birkenhead Docks. Eachleaf of this bridge had a central hydraulic press of sufficientpower to lift the leaf, and acting at the same time on the pivotupon which the bridge revolved. The tail end of the bridge