Throughout human history, the sea has yielded an abundance of resources for man's existence and has provided efficient routes for exploration and transportation. In return, it has exacted a toll in terms of human life and property. The fear and respect that it earned from those who ventured out upon its surface was itself a deterrent to learning more about its mysteries. The physical restrictions of penetrating the sea made sub-surface exploration nearly impossible. The most immediate restriction was air supply. Only the most disciplined divers could stay under for more than a few minutes. As scientists began to recognize the sea as a realm to be explored, this was their first hurdle. In 1716, the English astronomer, Edmund Halley, whose interests in the universe included Earth, invented a wooden diving bell which was open at the bottom. The significance of Halley's bell was the system developed with it...