Complex sentence: The first instrument used for deep-sea investigation was the sounding weight, used by British explorer Sir James Clark Ross, it reached a depth of 3,700 m (12,140 ft) in 1840.
Split into simpler sentences: The first instrument used for deep-sea investigation was the sounding weight, used by British explorer Sir James Clark Ross. It reached a depth of 3,700 m (12,140 ft) in 1840.