A thermometer measures temperature, by using materials that change in some way when they are heated or cooled. In a mercury or alcohol thermometer, the liquid expands as it is heated and contracts when it is cooled, so the length of the liquid column is longer or shorter depending on the temperature. Modern thermometers are calibrated in standard temperature units such as Fahrenheit or Celsius. Daniel Gabriel Fahrenheit (1686-1736) was the German Physicist who invented the alcohol thermometer in 1709 and the mercury thermometer in 1714. In 1724, he introduced the temperature scale that bears his name – Fahrenheit Scale.
The Celsius temperature scale is also referred to as the ‘centigrade scale’. The Celsius scale, invented by Swedish astronomer Anders Celsius, has 100 degrees between the freezing point (0oC) and boiling point (100oC) of pure water at sea level air pressure.