| Men and women have practiced breath-hold diving for | | | | brought under water was also tried, but it failed due |
| centuries. Indirect evidence comes from ancient | | | | to rebreathing of carbon dioxide. |
| artefacts of undersea origin found on land (such as | | | | In the 16th century, people began to use diving bells |
| mother-of-pearl ornaments), and depictions of divers | | | | supplied with air from the surface, probably the first |
| in ancient drawings. In ancient Greece breath-hold | | | | effective means of staying under water for any |
| divers are known to have hunted for sponges and | | | | length of time. The bell was held stationary a few |
| engaged in military exploits. Of the latter, the story | | | | feet from the surface, its bottom open to water and |
| of Scyllis (sometimes spelled Scyllias; about 500 B.C.) | | | | its top portion containing air compressed by the |
| is perhaps the most famous, as told by the 5th | | | | water pressure. A diver standing upright would have |
| century BC Greek historian Herodotus. | | | | his head in the air. He could leave the bell for a |
| During a naval campaign, the Greek Scyllis was taken | | | | minute or two to collect sponges or explore the |
| aboard ship as prisoner by the Persian King Xerxes I. | | | | bottom, then return for a short while until air in the |
| When Scyllis learned that Xerxes was to attack a | | | | bell was no longer breathable. |
| Greek flotilla, he seized a knife and jumped | | | | In 16th century England and France, full diving suits |
| overboard. The Persians could not find him in the | | | | made of leather were used to depths of 60 feet. Air |
| water and presumed he had drowned. Scyllis | | | | was pumped down from the surface with the aid of |
| surfaced at night and made his way among all the | | | | manual pumps. Soon helmets were made of metal to |
| ships in Xerxes's fleet, cutting each ship loose from | | | | withstand even greater water pressure and divers |
| its moorings; he used a hollow reed as snorkel to | | | | went deeper. By the 1830s the surface-supplied air |
| remain unobserved. Then he swam nine miles (15 | | | | helmet was perfected well enough to allow extensive |
| kilometres) to rejoin the Greeks off Cape | | | | salvage work. |
| Artemisium. | | | | Starting in the 19th century, two main avenues of |
| The desire to go under water has probably always | | | | investigation one scientific, the other technological, |
| existed: to hunt for food, uncover artefacts, repair | | | | greatly accelerated underwater exploration. Scientific |
| ships (or sink them), and perhaps just to observe | | | | research was advanced by the work of Paul Bert |
| marine life. Until humans found a way to breathe | | | | and John Scott Haldane, from France and Scotland, |
| underwater, however, each dive was necessarily | | | | respectively. Their studies helped explain effects of |
| short and frantic. | | | | water pressure on the body, and also define safe |
| One of the major hurdles of diving is to stay under | | | | limits for compressed air diving. At the same time, |
| water for a longer period of time. Breathing through | | | | improvements in technology - compressed air pumps, |
| a hollow reed allows the body to be submerged, but | | | | carbon dioxide scrubbers, regulators, and so forth - |
| reeds more than two feet long do not work well; | | | | made it possible for people to stay under water for |
| difficulty inhaling against water pressure effectively | | | | long periods. |
| limits snorkel length. Breathing from an air-filled bag | | | | |