Reversing thermometer

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.

It consists of a conventional bulb connected to a capillary in which a constriction is placed so that upon reversal the mercury column breaks off in a reproducible manner.

The mercury runs down into a smaller bulb at the other end of the capillary, which is graduated to read temperature.

The remote-reading potentialities of reversing thermometers make them particularly suitable for use in measuring subsea temperature as a function of pressure.