What device is used to measure temperature?

A thermometer is the device specifically designed to measure temperature. It operates on the principle of thermal expansion of substances, such as mercury or alcohol, which expand and contract with changes in temperature. This expansion allows for the measurement of temperature on a calibrated scale.

While barometers are used to measure atmospheric pressure and psychrometers are designed to measure humidity by comparing dry and wet bulb temperatures, hydrometers measure the density or specific gravity of liquids. Each of these instruments has a unique function related to different physical properties, distinguishing them from the thermometer, which exclusively focuses on temperature.