Bathyscaphe

A bathyscaphe is a free-diving, self-propelled deep-sea submersible, distinguished from the earlier bathysphere by hanging beneath a buoyant float rather than being lowered on a cable from a surface ship. The float is filled with gasoline, chosen because it is readily available, buoyant in water and, like any liquid, effectively incompressible even at extreme depth; the crew rides in a heavily built sphere slung underneath. To descend, the vessel floods ballast tanks with seawater, and to surface it releases iron shot ballast rather than relying on compressed air, which cannot overcome the enormous pressure of the deep ocean. The Swiss physicist Auguste Piccard invented the bathyscaphe and coined its name from Greek words meaning deep and vessel, building the first model, the FNRS-2, in Belgium between 1946 and 1948.