Meteorological instruments -- Measurement of Air Temperature
Liquid-in-glass thermometer is a thermometer in which the thermally sensitive liquid is contained in a graduated glass envelope. The indication of such a thermometer depends upon the difference between the coefficients of thermal expansion of the liquid and the glass.
For routine observations of air temperature, including maximum, minimum, dry-bulb and wet-bulb temperatures, liquid-in-glass thermometers are still commonly used. The liquid used depends on the required temperature range; mercury is generally used for temperatures above its freezing point (-38.8 degree Celsius), while ethyl alcohol or other pure organic liquids are used for lower temperatures. Mercury-in-glass type is usually used for meteorological purposes.