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.
Gas thermometer Gas thermometer A gas thermometer measures temperature by the variation in volume or pressure of a gas. This thermometer functions by Charles's Law. Charles's Law states that when the temperature of a gas increases, so does the volume. Using Charles's Law, the temperature can be measured by knowing the volume of gas at a certain temperature by using the formula, written below. Translating it to the correct levels of the device that is holding the gas. This works on the same principle as mercury thermometers. or T is the temperature. V is the volume. k is the constant for the