a deep-sea mercury-in-glass thermometer for measuring the water temperature at various depths.

The bore of a deep-sea reversing thermometer has a γ-shaped constriction above the bulb, after which it broadens, forms a loop, and then becomes an ordinary cylindrical channel ending in a slight expansion. After the reading of the thermometer has been established, the instrument is sharply turned upside down, which causes the separation of the column of mercury that had entered the bore through the constriction. The length of the mercury column in the bore is an indicator of the temperature. The loop prevents additional mercury from entering the bore from the bulb upon an increase in temperature in higher layers of water. An ordinary thermometer is mounted inside the protective glass tube of a reversing thermometer to show the temperature at the moment when the reading is taken and to introduce corrections to the readings of the reversing thermometer.