Engineering Wonders of the World
Volume I

36 ENGINEERING WONDERS OF THE WORLD. pumped to expel the water, and enable work to be carried on without having to employ compressed air in the entire space under the dome. The great cylinder was constructed on the river-bank and floated into position, being finally sunk into the river-bed in June 1854. Delay in penetrating the mud Sinking wag caugej by an oyster-bed, the „ . which had to be cut through by Cylinder. 6 J one edge of the cylinder. It had been ascertained that the surface of the rock dipped to the south-west to the extent of about 6 feet in the width of the pier, and the cylinder bottom was therefore made oblique so as to correspond ; but even when the rock was reached some irregularities of the surface caused the cylinder to tilt con- siderably from a vertical position, making necessary the use of the pneumatic apparatus to gain access to the rock and excavate in it a suitable resting-place for the cylinder. By February 1855, however, the latter had been sunk to its full depth, and then rested on solid rock ; but much trouble was caused by a spring of water issuing from a fissure in the rock, which had to be stopped with timber piles. This done, a ring of masonry was built, the mud enclosed removed by suction, and the space built up. Finally, towards the end of the year 1856, the masonry was completed to the cap of the pier, situated about 12 feet out of the water, and the upper part of the cylinder was unbolted and taken ashore, thus completing the difficult initial task. Meanwhile arrangements had been progress- ing for providing the ironwork for the centre spans that were to form a striking and by no means inharmonious feature in the landscape. Each of the two main girders was formed of a A GIRDER BEING ERECTED BESIDE THE RIVER. By permission of Mr. T. H. Quick,