Mercury-in-glass thermometer related to the rapid cooling (and contraction) of the glass. When Celsius decided to use his own temperature scale, he originally defined his scale "upside-down", i.e. he chose to set the boiling point of pure water at 0 °C (212 °F) and the freezing point at -100 °C (-32 °F). One year later, Frenchman Jean-Pierre Christin proposed to invert the scale with the freezing point at and the boiling point at . He named it Centigrade (100 grades). Finally, Celsius proposed a method of calibrating a thermometer: These points are adequate for approximate calibration but both vary with atmospheric pressure.
Six's thermometer and minimum scales; this shows the current temperature and should be the same on both scales. If the two readings are not the same, then the instrument scales are not correctly positioned or the instrument is damaged. The maximum and minimum readings are recorded by two small steel markers which are sprung into the capillary tube so that they can slide, but only if a force is applied to them, either by being pushed by the mercury or under the influence of an external magnet. Before a new maximum or minimum reading can be taken, the thermometer must be reset