Sounding technique used by Sir James Clark Ross in obtaining first modern
deep sea sounding on January 3, 1840 at Latitude 27 26 S and Longitude 17 29 W.
The observed depth was 2,425 fathoms. On January 22, 1968, the ESSA Ship
DISCOVERER sounded at the same location with a modern echo-sounder and measured
2312 fathoms, less than a 5 per cent error for Ross's observation.