Skip to content


Tool of the Times

Tool of the Times

September 8, 2013

Early in the twentieth century, oceanographers used a device called a bathythermograph (BT) to record water temperature beneath the surface on glass slides coated with smoke and oil to. Invented in the late 1930’s, the re-usable probes preserved information that proved critical to the U.S. Navy’s growing fleet of submarines and anti-submarine activities. As the metal BT dropped through the water, a bellows contracted under the increasing pressure, moving the attached slide along one axis. Another  component changed shape as temperature changed, moving a stylus that scratched a line in the coating. The resulting plots could then be interpreted with gridded readers, as in this 1940 photo.(Photo courtesy of Woods Hole Oceanographic Institution Archives)

Image and Visual Licensing

WHOI copyright digital assets (stills and video) contained on this website can be licensed for non-commercial use upon request and approval. Please contact WHOI Digital Assets at or (508) 289-2647.