Bathyscaphe

A bathyscaphe () is a free-diving, self-propelled deep-sea submersible, consisting of a crew cabin similar to a bathysphere, but suspended below a float rather than from a surface cable, as in the classic bathysphere design. The float is filled with gasoline because it is readily available, buoyant in water, and, like any liquid, practically incompressible. The incompressibility of the gasoline means the tanks can be very lightly constructed, since the pressure inside and outside the tanks equalizes, eliminating any differential. By contrast, the crew cabin must withstand a huge pressure differential and is massively built. Buoyancy at the surface can be trimmed easily by replacing gasoline in the tanks with water, because water has a greater density. Auguste Piccard, inventor of the first bathyscaphe, coined the name bathyscaphe from the Ancient Greek words βαθύς (bathús), meaning 'deep', and σκάφος (skáphos), meaning 'vessel, ship'.