UNDERSEA AND AERIAL TRANSPORT
Undersea craft such as diving bells and submarines developed surprisingly early. The first recorded reference to human underwater activities is credited to the pseudo-Aristotlian author of “Mechanical Problems” where the “tubes used by divers” are compared to an elephant's trunk. It is said that Aristotle's pupil, Alexander the Great, descended into the Bosporus in a large barrel to observe the marine life. Alexander Neckham (1157–1217) has an illustration of Alexander the Great inside a giant glass vessel with the interior lit by suspended tallow lamps, and fantastical marine creatures surround the vessel. A little later Roger Bacon (1214–97) mentions “machines for walking in the sea, even to the bottom, without danger to life or limb”.
The military advantage of being able to sink under the waves and reappear at a later time is considerable and the commercial possibility of being able to descend to a wreck to rescue valuables is also very great. Leonardo da Vinci sketched many divers' suits, some of which had provision to supply air for breathing while submerged. The example illustrated in Fig. 13.1 is of a diver and a boring machine with which he is to bore through the hull of an enemy ship without being seen. The diver is clad in a voluminous suit, which evidently contains sufficient air for a short mission but is not otherwise supplied with breathing facilities. It seems rather fanciful.
Kemp (1988, 192) says that William Bourne, writing in 1578 was the first to appreciate the principle on which a submarine operates and to describe how such a ship could be constructed. It is not known if Bourne's submersible ship was ever attempted, but interest in underwater devices was developing. Francis Bacon described a diving bell in 1620. It was a “sort of metal barrel lowered into the water open end downwards”. This sounds very like a diving bell seen about 40 years later by John Evelyn (Diaries, 1661); he writes “We tried our Diving-Bell or engine, in the dock, at Deptford, in which our curator continued half an hour under water; it was made