To explore even deeper depths, deep-sea explorers must rely on specially constructed steel chambers to protect them. The American explorer William Beebe, also a naturalist from Columbia University in New York, working with fellow engineer Otis Barton of Harvard University, designed the first practical bathysphere to observe marine species at depths that could not be reached by a diver. In 1930 Beebe and Barton reached a depth of , and in 1934. The potential danger was that if the cable broke, the occupants could not return to the surface. During the dive, Beebe peered out of a porthole and reported his observations by telephone to Barton who was on the surface.