Middlesex-born Edmond Halley (1656-1742), of comet fame, invented the continuously-air-supplied diving bell in 1691. Before this, diving chambers, shaped like open-bottom bells, had only the air that was initially trapped inside them on being carefully lowered into the water.
Halley’s bell was wooden and had lead weights. There was a bench above the lower rim and leather barrels of air with leather tubes were fed down one after the other by assistants on the water’s surface. These were pulled up into the bell, at which point the increased air pressure would push the new air out into the tubes. These could be attached to a diving helmet, also invented by Halley, or released into the bell. A stopcock in the bell’s roof allowed for expulsion of spent air.
Yorkshireman John Smeaton, FRS (1724-92), who had become the ‘father of civil engineering’ in his illustrious career, designed an air pump in his later years that could be attached to the bell, thereby improving its efficiency even further. These ideas opened up the underwater world and enabled salvage, rescues and exploration, as well as the construction and repair of rigs, lighthouses and bridges. Today, depths of 30-500ft. are usual, though 2,300ft. is the record.
(Image: Wellcome Library, London, at Wikimedia Commons / CC BY 4.0)