- a spherical diving apparatus from which to study deep-sea life, lowered into the ocean depths by a cable.
- a strong steel deep-sea diving sphere, lowered by cable
- A hollow, spherical steel diving chamber in which people are lowered by cable from a surface vessel to explore the ocean depths. In 1934 a bathysphere carrying William Beebe and an associate reached a record depth of over 923 m (3,028 ft). Because space in the bathysphere is cramped, dives longer than three-and-a-half hours are intolerable, and it was eventually supplanted by the bathyscaphe.