thermometer

Clinical thermometer. When the bulb of the thermometer is placed under the tongue of the patient, the mercury in the bulb expands and forces a column of mercury of the scale tube. When the thermometer is removed for inspection, the mercury in the bulb contracts but that in the tube cannot cannot flow back past the neck: the reading thus stays the same. The thermometer is reset by centrifugal shaking.

An instrument for measuring the temperature of a substance on some reproducible scale. Its operation depends upon a regular relationship between temperature and the change in size of a substance (as in the mercury-in-glass thermometer) or in some other physical property (as in the platinum resistance thermometer). The type of instrument used in a given application depends on the temperature range and accuracy required.

Related entries

   • Beckmann thermometer
   • pyrometer
   • thermograph

Related categories

• HEAT AND THERMODYNAMICS
• INSTRUMENTATION

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