A thermometer is used to measure the temperature of solids, liquids, or gases. A thermometer contains a liquid (usually mercury or an alcohol solution) in a reservoir whose volume is linearly dependent on the temperature (as the temperature increases, the volume increases). When the liquid is heated it expands into a narrow tube that has been calibrated to indicate the temperature. Temperature can be recorded in Celsius, Farenheit, or Kelvin, therefore it is important to note which scale the thermometer is calibrated for.
