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The Celsius scale is one of the most widely used temperature scales around the world. It measures temperature in terms of degrees Celsius, represented by the symbol °C, which was originally defined as one hundredth of the temperature difference between the freezing point and the boiling point of water.
This temperature scale is used today in almost every country in the world, except for five that still use the Fahrenheit scale. Additionally, it is the temperature scale that is used par excellence in the natural sciences.
However, there is a second scale that always comes up when talking about the Celsius scale, and that is the centigrade scale. But isn’t the centigrade scale the same as the Celsius scale? The answer to this question is both yes and no. It could be said that degrees Celsius is the way degrees Celsius were formerly called. However, the relationship between these two temperature units is a bit more complex, as there is a subtle difference between the two that is the subject of this article.
The original Celsius scale or centigrade scale
The invention of the Celsius scale is credited to the Swedish astronomer and physicist Anders Celsius. Celsius proposed in 1742 a temperature scale that took as reference points the melting temperature of ice (or, what is the same, the freezing point of water) and the boiling point of water at sea level, that is, , at a pressure of about 1 atm.
Celsius recognized that the boiling point of liquids varied with pressure, so his way of defining temperature was much more reproducible than what Fahrenheit had defined nearly 20 years earlier.
To simplify its use and interpretation, Celsius decided to divide the aforementioned temperature range by 100 units, which he called degrees Celsius, which literally means divided by 100 degrees. Years later and after his death (somewhat prematurely at 42 years of age, by the way), they were named degrees Celsius in his honor and in recognition of his many contributions to science.
So far everything seems normal and it is clear that degrees Celsius and degrees Celsius are actually the same thing. It is highly probable that whoever is reading this article has heard this story more than once. However, there is a peculiarity regarding the way in which Celsius defined the scale of it; few know about it because it goes against not only the current definition of degrees Celsius but even common sense.
For some inexplicable reason, in his original work, Celsius defined the boiling point of water as 0 on his scale and the freezing point as 100. This is surprising and completely counterintuitive, since it is evident that boiling water is at a higher temperature than ice at its melting point.
The contribution of Carolus Linnaeus
Despite the awkward definition of the scale’s reference points, the potential to simplify the interpretation of temperature measurements using the Celsius centigrade scale was apparent. Celsius died two years after publishing his temperature scale, and almost immediately the Swedish taxonomist Carolus Linnaeus proposed what was on the minds of all scientists at the time: that the Celsius scale be reversed. Thus, the melting point of water was set as 0 on the scale and the boiling point as 100.
From that moment on, the centigrade temperature scale began to spread throughout the scientific community around the world and, eventually, among the rest of the population.
The birth of the current Celsius scale
For 200 years the temperature scale invented by Celsius and inverted by Linnaeus was called the centigrade scale, as its creator had called it. However, in 1948, the General Conference on Weights and Measures proposed renaming the scale’s degrees to degrees Celsius in honor of its creator.
In that same conference the reference points of the scale were also changed. In fact, starting in 1948, the new Celsius scale ceased to be an independent temperature scale with its own reference points and began to depend on the absolute temperature scale or Kelvin scale. This scale is defined based on the triple point of water (temperature and pressure conditions in which the three phases coexist: solid, liquid and gas).
This temperature was defined as exactly 273.16 K, so that the normal melting point of water would be 276.15 K. This temperature is now defined as zero on the new Celsius scale, or 0 °C. .
Simply put, the zero of the Celsius scale remains the same as the original centigrade scale (ie after the Linnaeus inversion). However, the second point of reference ceased to be the boiling point of water and became the zero of the thermodynamic temperature scale or absolute zero, corresponding to -273.15 °C.
Conclusion
Degrees Celsius and degrees Celsius are two closely related units of temperature. The original concept of the creator of the centigrade scale, Anders Celsius, does not coincide with what we now commonly know as degrees Celsius or, for that matter, with what we know as degrees Celsius. This is because Celsius, for some reason, defined the scale of it inverted giving it a value of 100 at the freezing point and 0 at the boiling point of water.
Despite this, the fact that the scale was “corrected” shortly after its creation and became popular as we know it today means that this early inverted form of the centigrade scale has been buried in the annals. of the history of science.
However, there is still a fundamental, albeit subtle, difference between the corrected Celsius scale that was used for over 200 years and what we know as the Celsius scale today. The original was an independent temperature scale defined in terms of the melting and boiling points of water; while the second, the Celsius scale, is a subordinate scale to the Kelvin scale and, therefore, no longer depends on the melting and boiling points of water but on the triple point and absolute zero that define said absolute scale of temperature.
Despite this, the new definition of degrees Celsius is such that the melting point of water is still zero on the scale (0°C) and the boiling point is still 100°C, at least to the second decimal place. . For this reason, there is no significant difference between the two units of temperature and, for all practical purposes, they can be used interchangeably as if they were the same unit.
References
- Brannan. (2021, April 1). Difference between Celsius, Centigrade and Fahrenheit? Retrieved from https://www.brannan.co.uk/celsius-centigrade-and-fahrenheit/
- MacDonald, J. (2016, November 27). The Legacy of Anders Celsius . Retrieved from https://daily.jstor.org/the-legacy-of-anders-celsius/
- National Institute of Standards and Technology. (2021a, June 3). Kelvin: Introduction . Retrieved from https://www.nist.gov/si-redefinition/kelvin-introduction
- National Institute of Standards and Technology. (2021b, June 3). SP 330 – Appendix 1 . Retrieved from https://www.nist.gov/pml/special-publication-330/sp-330-appendix-1
- National Institute of Standards and Technology. (2021c, July 12). SI Units – Temperature . Retrieved from https://www.nist.gov/pml/weights-and-measures/si-units-temperature
- Shampoo, MA, & Kyle, RA (1993). Anders Celsius—Temperature Scale. Mayo Clinic Proceedings , 68 (11), 1125. Retrieved from https://www.mayoclinicproceedings.org/article/S0025-6196(12)60910-0/fulltext#relatedArticles
- Wild, S. (2021, March 22). What is temperature? Facts about Fahrenheit, Celsius and Kelvin scales . Retrieved from https://www.livescience.com/temperature.html
- Specialists in Metrology SAS Why degrees Celsius and not degrees Celsius? Retrieved from https://www.especialistasenmetrologia.com/por-que-calibrar-con-un-laboratorio-acreditado-4.html .
