19 May 1743

Jean-Pierre Christin developed the “centigrade” temperature scale.

Jean-Pierre Christin a French physicist, mathematician, astronomer and musician improved the Celcius scale thermometer. His proposal to reverse the Celsius thermometer scale from water boiling at 0 degrees and ice melting at 100 degrees, to water boiling at 100 degrees and ice melting at 0 degrees was widely accepted and is still in use today.

Christin was born in Lyon. He was a founding member of the Académie des sciences, belles-lettres et arts de Lyon and served as its Permanent Secretary from 1713 until 1755. His thermometer was known in France before the Revolution as the thermometer of Lyon. One of these thermometers was kept at Science Museum in London.

In 1742, Swedish astronomer Anders Celsius created a temperature scale which was the reverse of the scale now known by the name “Celsius”: 0 represented the boiling point of water, while 100 represented the freezing point of water. In his paper Observations of two persistent degrees on a thermometer, he recounted his experiments showing that the melting point of ice is essentially unaffected by pressure. He also determined with remarkable precision how the boiling point of water varied as a function of atmospheric pressure. He proposed that the zero point of his temperature scale, being the boiling point, would be calibrated at the mean barometric pressure at mean sea level. This pressure is known as one standard atmosphere. The BIPM’s 10th General Conference on Weights and Measures later defined one standard atmosphere to equal precisely 1013250dynes per square centimetre.