Actual or projected routes for telegraph cables across the deep sea have also been sounded with extreme accuracy in many cases; but beyond these lines of sounding the vast spaces of the ocean remain unplumbed save for the rare researches of scientific expeditions, such as those of the " Challenger," the " Valdivia," the " Albatross " and the " Scotia."
The underground system of paper cables has been very largely extended, Cables between London, Glasgow, Edinburgh, Liverpool.
All cables of any great length are worked by reverse currents.
Two submarine cables start from Otranto, one for Valona, the other for Corfu.
Brewing, saw-milling, boat-building, and the manufacture of biscuits, soap and submarine cables are also carried on.