thermometer

Maximum and minimum thermometers are universally used in weather-reporting stations. The maximum thermometer, shown here, includes a magnet that fits tightly inside a capillary tube and is moved up the tube by the rising mercury. When the temperature falls, the magnet remains in position, thus enabling the maximum temperature to be recorded.

Instrument for measuring temperature. There are many types, designed to measure different temperature ranges to varying degrees of accuracy. Each makes use of a different physical effect of temperature. Expansion of a liquid is employed in common liquid-in-glass thermometers, such as those containing mercury or alcohol. The more accurate gas thermometer uses the effect of temperature on the pressure of a gas held at constant volume. A resistance thermometer takes advantage of the change in resistance of a conductor (such as a platinum wire) with variation in temperature. Another electrical thermometer is the thermocouple. Mechanically, temperature change can be indicated by the change in curvature of a bimetallic strip (as commonly used in a thermostat).