Thermometer is device used to measure temperature.

Liquid thermometer benefits from thermal expansivity of liquids (e.g. mercury or spirit). As liquid thermometer we class certain room and clinical thermometers. Disadvantage of mercury thermometer is necessity of careful manipulation because breaking up jar containing measuring liquid leads to evasion of substance whose fumes are toxic.

Bi-metal thermometer compose of two standing in metal pieces of tin which creep depending on temperature each one differently. When temperature changes metal girdle crooks and depending on it shows temperature on scale.

Resistance thermometer utilizes electrical conductor or semiconductor resistance dependence on temperature

Thermoelectric thermometer (thermocouple) operates with Seebeck effect. Temperature change of two metals joint leads to change of rising thermoelectric tension. Mostly used combinations of metals are copper and constantan (alloy of copper with nickel), iron and constantan, nickel-chrome and nickel or platinum and alloy of platinum with rhodium.

Gas thermometer makes use of the gas pressure dependence on its temperature when the volume of body is constant or the volume of body dependence on its temperature when the gas pressure is constant.

Infrared thermometer (sometimes called radiation thermometer) measures radiance beamed by objects to their surroundings. It manages to measure temperature of objects without physical contact.
Easy and Quick Conversion of Temperatures between Scales
(c) Jan Zaškolný 2008