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water temperature

Although the principle of the reversing thermometer had been described by scientists as early as 1845, this Negretti and Zambra thermometer was the first thermometer to accurately determine the temperature at great depth and return to the surface and retain its readings. As such, it is considered the first modern reversing thermometer. This was the reversing thermometer sent to scientists and used on the Challenger expedition.

This thermometer was housed in a helical mounting mechanism meant to cause the reversing thermometer to flip at the required depth. A helical screw would measure the depth on the way down and release the mounting at the desired depth.


 
Negretti and Zambra thermometer, 1874 model
Photographer: Y. Berard
Photo: Oceanographic Museum of Monaco .