Compressed Air Work And Diving 1909

IIALLE Y S BELL. 33 cask. It coulcl not escape through the top hole because the end of the pipe was kept below the bottom of the cask. When the beil was reached the pipe was taken hold of and lifteel up underneath the beil. The water then rose in the cask and forcecl the air into the beil at the requireel pressure. Halley’s Bell was in the form of a truncated cone, and was made of wooel, with a capacity of about 60 cub. ft. The top was fittecl with a glass winelow, and a valve to let out the fbul air. When making a descent, Halley used to stop every 12 ft. and have casks sent clown until the water which had risen in the beil had been driven out. Then he would clescencl another 12 ft. On one occasion, in company with four others, he descencled to a clepth of 54 ft., and was below one and a half hours. In 1778 John Smeaton clevisecl a beil with which to underpin the foundations of a bridge over the Tyne at Hexham which had been injured by a flooel. This bell in some respects more resembled a caisson than a cliving bell, as it was not intended to be entirely submerged. It was 4 ft. 6 in. high only, and 3 ft. 6 in. long, and had on the top a 10-in. diameter force pump for supplying air. Light was obtaineel from five circular glass Windows at the top, Fig. 1. Smeaton afterwards used a bell at Ramsgate harbour,* and after his death, when the work was taken over by Rennie, the bell was mueh improveel, and it was used for the whole of the construction of the East Pier, which was founded 17 ft. below water. Rennie also used his bell at Holyhead, Howth, and Sheerness harbours, and also at Plymouth dockyard. Rennie’s bell was made of cast iron. The moclern cliving bell is built up with mild Steel * Proc. List. C. E., vol. v. C