A bathyscape is basically a bathysphere — a thick-armored metal sphere for diving — bolted to the bottom of a float, or a buoying device used to change depth. The bathyscape is used for investigating the deep sea. The most famous is the bathyscape Trieste, which reached the deepest point on the Earth's surface, the Challenger Deep in the Mariana Trench, carrying two passengers, Jacques Piccard and Lt. Don Walsh. So few bathyscapes have been built that the term is most often associated specifically with the Trieste.
The bathyscape began with the construction of the first bathysphere, devised by Otis Barton in 1928. The first bathysphere was hollow, with walls of one inch thick (2.54 cm)cast steel, 4.75 ft (1.5 m) in diameter. Fused quartz, which the strongest transparent material available at that point, was used for the windows. Instead of being self-propelled like the Trieste, this early bathysphere was lowered into the depths on a tether. Oxygen was provided via a pressurized canister on the outside of the sphere, and carbon dioxide removed by electric fans circulating the air over pans containing soda lime.
The bathyscape was an improvement on the bathysphere, devised by the Swiss physicist, inventor, and explorer Auguste Piccard. Initially interested in building atmospheric balloons, Piccard realized that a modification of some of these concepts would allow construction of a craft that could descend into the deep ocean. After extensive trial-and-error from the mid-30s to the mid-50s, Piccard invented a bathyscape suitable for use by the French Navy, which used it to send a man safely down to 4,176 m (13,700 ft). This is very impressive, and even the strongest modern nuclear subs have a crush depth of 730 m (2,400 feet).
The float portion of a bathyscape is filled with petrol, which is nearly incompressible. As the bathyscape descends, it discharges petrol, replacing it with water, decreasing the buoyancy of the craft. Buckets of iron shot are held inside the craft via electromagnets. Once the craft reaches the bottom, this shot is released to ascend. This is a fail-safe mechanism -- even if the power fails, the shot is released anyway, so no one is trapped at the bottom of the ocean.
The term bathyscaphe was made using the Greek words bathys ("deep") and skaphos ("ship"). Since the Trieste retired, most deep-sea submersibles have been robotic only.