Hydra weight-detaching sounder for collecting small samples from the sea bottom, of the type designed by Mr Gibbs, Artificer aboard the sounding ship HMS Hydra, 1868, and used in sounding operations in the Atlantic and Indian Oceans. Hydra sounders were also employed by naturalists Charles Wyville Thomson, William Benjamin Carpenter and J Gwyn Jeffreys on HMS Porcupine in investigations of deep sea life in 1869. The instrument’s iron sinking weights are represented by wooden models.

The sturdy Hydra sounder collected small samples of bottom water in the tube above the sediment plug, the latter retained by a butterfly valve. This arrangement worked well on fine-grained sediments.

The cruises of HMS Porcupine were initiated by the Royal Society with the cooperation of the Admiralty and followed a cruise the previous year by HMS Lightning. They carried out dredging operations to investigate sea bottom temperatures and the organisms in the deep sea. The scientists aboard Porcupine also carried out chemical analyses of seawater samples.