Bathyscaphe

To descend, a bathyscaphe floods air tanks with sea water, but unlike a submarine, the bathyscaphe cannot displace the water in the flooded tanks with compressed air to ascend, because the water pressures at the depths in which the craft was designed to operate are too great. For example, the pressure at the bottom of the Challenger Deep is more than seven times that in a standard "H-type" compressed gas cylinder. Instead, ballast in the form of iron shot, which is well over seven times as dense as seawater, is released to allow ascent, the shot being lost to the ocean floor. The iron shot containers are in the form of one or more hoppers which are open at the bottom throughout the dive, the iron shot being held in place by an electromagnet at the neck. This is a fail-safe device as the craft requires no power to ascend; in fact, in the event of a power failure, shot runs out by gravity and ascent is automatic. ==History of development==

The first bathyscaphe was dubbed FNRS-2, named after the Fonds National de la Recherche Scientifique, and built in Belgium from 1946 to 1948 by Auguste Piccard. (FNRS-1 had been the balloon used for Piccard's ascent into the stratosphere in 1938). Propulsion was provided by battery-driven electric motors. ==Accomplishments==

In 1960 Trieste, carrying Piccard's son Jacques Piccard and Don Walsh, reached the deepest known point on the Earth's surface, the Challenger Deep, in the Mariana Trench in the Pacific Ocean. This put to rest the question of whether or not there was life at such a depth in the complete absence of light. == See also ==