Once upon a time, zero degrees didn’t mean what we think it does today. In the realm of temperature scales, the fascinating story of the Celsius scale’s evolution stands out. With its origins steeped in scientific inquiry and a touch of serendipity, the tale of how zero degrees came to mark the freezing point of water rather than its boiling point is one of the great twists in scientific history.
Back in 1742, the Swedish astronomer Anders Celsius developed a temperature scale which was the reverse of what we use today. In a notable paper titled “Observations of two persistent degrees on a thermometer,” Celsius built his scale with zero degrees representing the boiling point of water and one hundred degrees the freezing point, under a standard atmospheric pressure. But why the inversion? Celsius was zeroing in on a constant reference point based on atmospheric conditions. 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.
However, the scale as Celsius proposed it would not last. Upon his death in 1744, the Swedish botanist Carl Linnaeus, recognized for his taxonomic work, sought a more intuitive approach and reversed Celsius’s scale so that zero degrees signified the freezing point of water and one hundred degrees the boiling point. This inversion was essentially a twist of fate for the Celsius scale, making it far more practical and intuitive for everyday use.
By 1948, the International Committee for Weights and Measures adopted the term “degree Celsius” in honor of its creator and to eliminate confusion with angular measurement in some languages.
The scale’s link to water’s boiling and freezing points was solidified when the 9th General Conference on Weights and Measures defined the triple point of water as 0.01 °C in 1948. However, this relationship was later changed. In 2019, the definition was modified to be based on the Boltzmann constant, which fully decoupled the Celsius scale from the properties of water.
Relevant articles:
– TIL that originally celsius degrees were meant to be reversed with water boiling at zero degrees and freezing at 100