Model diving bells, early 18th century.
© Science Museum / Science & Society Picture Library
The glas model on the left has twelve lead weights which kept it submerged. The wire cage was used to contain small birds or mice so that the bell could be seen in action. It is asociated with Dr Stephen Demainbray (1710-1782), a science lecturer of the time. The other model, made of green and blue painted tinplate, is of the diving bell devised by Edmond Halley (1656-1742). Halley developed a system whereby air was lowered to the occupant of the diving bell in barrels, and used air was let out of the bell via a stopcock. This meant that divers could stay underwater for much longer than if they had to rely exclusively on the air that was in the diving bell when it first submerged.