ABSTRACT
A human diver trying to follow the example of a duck or a seal or a beaver must surely have been disappointed in his own performance. The most obvious handicap of the human diver is the fact that he is an air-breathing mammal who largely lacks the special adaptations that enable other diving animals to surpass him as a diver. A human being can remain underwater without breathing apparatus only as long as he can hold his breath; and even with lifelong training, his breath-holding time remains only a few minutes at best. If the diver can coax his eustachian tubes to open, air from the upper part of his throat will enter the middle ear spaces and bring the pressure there up to the same level as the pressure in the water outside. Practical self-contained underwater breathing apparatus also has a surprisingly long history.
