130 HYDRAULIC POWER APPLIED TO BRIDGES.

centre pier. This cap rests on the top of six cast iron columns,7 feet ia diameter, which are arranged in a circle and form thecentre pier. A centre column BB, also 7 feet in diameter, con-tains the accumulator, and is attached to the others by cast ironstays which support a floor. On this the steam-engine, boilers,&c., for producing the hydraulic power are fixed.

The weight of the swing-bridge is 670 tons, and it restsentirely on a circle of 26 conical live rollers, EE. These are3 feet in diameter, with 14 inches width of tread, and runbetween the two circular roller-patlis, DD, which are 32 feet indiameter and 15 inches wide.

The turning motion is communicated to tlie bridge by a bevilwheel H, which gears into a cast iron circular rack, G, bolted tothe outer circumference of the upper roller path. A steel pinJ, supported in the lower roller path, carries the bevil wheel.This is driven by a piniou connected by intermediate gearingwith a three-cylinder hydraulic engine (in duplicate) placed atKK, which exerts a force of about 10 tons at the radius ofthe roller path. The engines work at 40 revolutions per minute,with a water-pressure of 700 lbs. per square inch. The poweris obtained from a pair of 12 HP steam-engines fixed (as beforestated) in the engine-room formed beneath the centre of thebridge. Water is delivered into the accumulator C, which hasa ram 16| inches in diameter and 17-feet stroke, and is loadedwith a weight of 67 tons.

To secure a solid roadway, and a perfect continuity of theline of rails, an arrangement of gearing, shown by Plate 29,figs. 1, 2, 3, and 4 is used. By this each extremity of thebridge is slightly lifted by a horizontal hydraulic press N, actingon the levers PP, forming a “toggle joint.” The press has tworams acting in opposite directions upon two toggle joint-levers,connected by a bar Q, which moves in a vertical guide to insurea perfectly parallel action of the two points. By this means theend of the bridge is made truly parallel when the resting-blocksIIP, under each girder, are put into position. To do this, threeseparate hydraulic cylinders, SS, are employed, as shown by figs.