Reversing thermometer

A reversing thermometer is a mercury-in-glass thermometer which, unlike most conventional mercury thermometers, has the unique ability to record a temperature for later viewing. When inverted, these thermometers capture and display the current temperature until they are returned to their upright position. From around 1900 to 1970, reversing thermometers were the primary instruments oceanographers relied on to measure water temperatures beneath the ocean's surface.

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