In 1872, the final link in a cable joining Adelaide and London was made using the newly invented telegraph. To reach this stage, engineers and explorers had hacked their way through the forests of Borneo, tramped across the blistering deserts of central Australia and pioneered new marine cable-laying technology. Physicist and writer Paul Davies uses the latest satellite technology to re-link the ends of the original cable and hear the epic story of its Construction. Producer Martin Redfern