There was a meme out a while back, pointing out the differences between Fahrenheit, Celsius, and Kelvin. Measuring was a challenge in those early days – heck, measuring was a challenge to me after I had completed college classes on the topic. Somewhere in the Glen Lake Irrigation District files of “as built” projects, my blunder on the Tamboer Siphon may still be recorded – I carefully picked the best spot for an inlet structure, numbered it 0+00 and began surveying. A couple weeks later, I realized that I needed shots further upstream and had to start using negative numbers to finish the project. It was a solution, but not an elegant solution. After the experience, I started at 10+00. Less mockery occurs when your mistakes aren’t so obvious.
Anders Celsius made a similar blunder – he set the boiling point of water at 0 degrees and the freezing point at 100 degrees. Then as he continued his studies, he found that the boiling point of water changes with elevation (atmospheric pressure) while the freezing point of water was independent of both latitude and atmospheric pressure. After Celsius died, the Royal Swedish Academy of Sciences noted that Celsius’ successors had reversed the measurements. It does make more sense to start measuring from something constant.
The amazing thing about the Fahrenheit scale is that it came first. Without a consistent scale on the thermometer, the extra energy involved in shifting from water to ice (or vice versa) makes precise and accurate measurements somewhere between difficult and impossible. Fahrenheit chose to set his zero at the point that the reaction between ice, water and ammonium chloride quit working. Once he had that, and marked his thermometer, he could repeat his experiment and determine that he had a consistent zero, based on a chemical reaction. His next line was assuming the human body temperature was 100 degrees. Then he could measure the temperature of ice water. A bit of refinement, and freezing became 32 degrees, body temperature 96 degrees, and individual degrees could be measured by cutting the difference in half – 32 to 16, 16 to 8, 8 to 4, 4 to 2, and in 5 steps Fahrenheit had the gradations on his thermometer. In the US we still use his method, though the rest of the world uses the modification of the Celsius system.
William Thompson (Baron Kelvin) came up with the Kelvin scale in 1848 – where zero was based on his calculations of absolute zero. Thompson’s calculations showed absolute zero at -273 degrees centigrade. In the following century and a half, his calculations have been corrected to -273.15.
All told, it’s kind of humbling to see what these folks could do in the 18th and 19th centuries, without calculators and computers. Thermometers of sorts were invented long before – but developing a universal measuring scale was long in coming.