You searched for: “bathythermosphere
bathythermosphere (s) (noun), bathythermospheres (pl)
A device or instrument for recording the temperature against the depth (pressure) in the ocean from a ship that is underway or in motion: A bathythermosphere, or BT, was used by senior students for scientific purposes for the university, and especially to find out the distribution of water temperature in relation to th deepness of the ocean.