May 192017


On this date in 1743 the Lyonnais physicist Jean-Pierre Christin, permanent secretary of the Académie des sciences, belles-lettres et arts de Lyon, working independently of the Swedish astronomer Anders Celsius (who had developed a similar (but inverted) scale), published the design of a mercury thermometer, the “Thermometer of Lyon” built by the craftsman Pierre Casati that used a scale where zero represented the freezing point of water and 100 represented the boiling point of water at one standard atmosphere. It was, and still is (sometimes), called the centigrade scale although more usually it is called the Celsius scale to honor the first creator even though his scale is not quite the same as the centigrade scale. I tend to vacillate between the two names because I grew up calling it centigrade which seems more etymologically satisfying to me – “centi” (100), “gradus” (degree). Honoring people is all right too, though, as for many SI units: joule, amp, volt, etc. etc. I’ll dribble on a bit about the history of the Celsius scale and then turn my attention to why the US is so resistant to the metric system when the rest of the world uses it more or less happily – even Britain, where such changes do not come easily.


As it happens, the Fahrenheit scale, developed by the Dutch-German-Polish physicist, inventor, and scientific instrument maker Daniel Gabriel Fahrenheit, was published only about 20 years before Celsius and Christin published details of their scales, because at that time there was a pressing need in science for accurate measurements of temperature. Fahrenheit’s scale had three calibration points: the freezing point of a stable mix of ice, water, and ammonium chloride  (0°F), the freezing point of distilled water (32°F), and mean human body temperature (96°F). The latter reference point was later shifted slightly higher. The boiling point of distilled water at one atmosphere was set at 212°F, making the range between the freezing and boiling points of water 180 degrees. 180 is a highly composite number (or anti-prime), meaning that it has numerous divisors, so that, in theory, the scale is useful for mathematical calculations that will result in whole number solutions to various equations.


In 1742 Anders Celsius (1701–1744) published details of  a temperature scale which was the reverse of the scale now known by his name: 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 documented 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.

In 1743 Jean-Pierre Christin published his work on a centigrade scale, and in 1744, coincident with the death of  Celsius, Swedish botanist Carolus Linnaeus (1707–1778) reversed Celsius’ scale, but otherwise kept the intervals between degrees the same. Here we have a, not very well known, example of a common habit of scientists coming up with the same results independently. In this case the coincidence is undoubtedly due to the fact that a metric system of measures across the board makes a great deal of sense for computational purposes. Time is the one variable that won’t play nice.

Linnaeus’ custom-made “linnaeus-thermometer,” for use in his greenhouses, was made by Daniel Ekström, Sweden’s leading maker of scientific instruments at the time and whose workshop was located in the basement of the Stockholm observatory. As it happens, numerous physicists, scientists, and instrument makers at the time are credited with having independently (or semi-independently) developed a centigrade scale; among them, Pehr Elvius, the secretary of the Royal Swedish Academy of Sciences (which had an instrument workshop) and with whom Linnaeus had been corresponding; Daniel Ekström, the instrument maker; and Mårten Strömer (1707–1770) who had studied astronomy under Anders Celsius.

The first known Swedish document reporting temperatures in the centigrade scale is the paper “Hortus Upsaliensis” dated 16 December 1745 that Linnaeus wrot