A diving bell is a chamber suspended by a cable that allows divers to stay underwater for long periods of time, thus avoiding the need to return to the surface repeatedly and risking decompression sickness. With increasing depth , the height of the level of water in the tank increases, compressing the air inside the chamber. Such a device was described by Aristotle.
The relation between the depth and the height is given by
where is the pressure, is the density of water, and is the acceleration due to gravity.