When I visit dad each week, he usually grumbles about how cold his room feels to him. He often wears long-sleeved shirts, even in the middle of August. At the same time, I think his room is too hot and stuffy. I wear short-sleeved shirts, even in the middle of December. I’ve often reflected about how many of my friends and family members have different levels of comfort.
Yesterday, I glanced at one of my vintage, liquid thermometers and pondered its two scales, Fahrenheit and Celsius. Eventually, I reminisced about my high school chemistry class and a lesson about temperature scales. During that week’s lessons, we learned about measuring hot and cold according to the Kelvin scale. We were taught how to convert Fahrenheit to Kelvin and Celsius to Kelvin with mathematical formulae.
This was difficult for me, because my math skills were sub-par. This was also at the time when hand-held electronic calculators were rare and students were prohibited from using them in class. All of our calculations had to be performed in long form on scratch paper, which was turned in at the same time as our assignments. Regardless of the technical obstacle, I was still fascinated about the different scales of temperature measurement.
In addition to Fahrenheit, Celsius, and Kelvin, I found out there were a couple of other scales that are rarely used, Rankine and Réaumur. All five of the scales were introduced within approximately the same era of history, the 18th and 19th centuries. They all were invented as ways to standardize scientific research.
The Rankine measurement was created in the 1800s by the Scottish engineer, W.J.M. Rankine. It had found favor in scientific communities for a short time, but was not universally practical. It is based on the Kelvin scale but calibrated according to Fahrenheit degrees.
The earlier Réaumur thermometer was developed by the French scientist R.A.F. de Réaumur in the late 1700s. Réaumur placed his zero mark at the freezing point of water while the boiling point of water was 80 degrees. The Réaumur scale was more commonly used by 17th and 18th century scientists than that of Rankine. The Réaumur scale is now largely obsolete.
The Fahrenheit scale is the one most familiar to people in the United States. It was first proposed in 1714, by the German physicist Daniel Fahrenheit, who lived most of his life in Holland. His zero point was based on the coldest temperature he could achieve with a mixture of ordinary salt and ice. Fahrenheit’s definition of 100-degrees was based on what was thought, at the time, to be the average core temperature of the human body. (We now know that our average core temperature is 98.6 Fahrenheit.) Fahrenheit’s methodology was somewhat imprecise, so the Fahrenheit scale has been adjusted since its original introduction.
Mr. Fahrenheit is also credited with the invention of the common mercury thermometer. His invention was derived from the original design theory and research by Galileo Galilei for a proposed barometric pressure and temperature measurement device.
The Celsius scale has a joint history. Swedish professor of astronomy Anders Celsius introduced a unique temperature scale, inverted according to modern standards. His zero point was the boiling point of water. His 100 was the freezing point of water. After Celsius’ death, in 1744, Celsius’ friend, the botanist, Carl von Linné (Linnaeus) adapted Celsius’ calibration to his own greenhouse thermometers. Linné’s change was zero for freezing and 100 for boiling.
On May 19, 1743, unaware of the work of the two Swedes, Jean Pierre Christin, in Lyon, France introduced his own thermometer. His zero point was also the freezing point of water and his 100 degrees was the boiling point of water. Even though the Réaumur thermometers were the most widely used instruments in France, Christin’s thermometers were exported outside the country. His devices were popularly called “Lyon Thermometers”.
The International Commission on Weights and Measures, in 1887, adopted the units created by Celsius, Linné, and Christin as the “standard thermometric scale for international services”. The commission defined the new Centigrade scale by means of a hydrogen thermometer with the fixed points of melting ice as 0° and the vapor of boiling, distilled water at one metre of murcury atmospheric pressure as 100°.
In 1954, the 10th General Conference of Weights and Measures renamed the Centigrade scale to Celsius, in honor of the Swedish professor’s work. It was renamed, in part, because the term “centigrade” is also a unit of geometric measurement.
Even Celsius isn’t quite precise enough for modern scientific needs. The Kelvin scale was invented as the latest benchmark in temperature measurement. The scale was named for the British scientist, William Thompson, Lord Kelvin. He was most widely acclaimed for his discoveries about heat in the 19th century.
Scientists have calculated that the very coldest temperature possible is minus 273.15 degrees Celsius. It is at this temperature that, theoretically, all molecular motion comes to a halt. On the Kelvin scale this is known as absolute zero (0 K). Unlike the other scales, there are no “minus zero” measurements possible on the Kelvin scale. Kelvin thermometers use the exact configuration as Celsius thermometers but the word “degree” is not used. To convert Celsius to Kelvin, you only need to add 273.
So, how hot or how cold are you? Go ahead, choose your scale.
The Blue Jay of Happiness likes Hermann Hesse’s philosophical take on temperature. “The bourgeois prefers comfort to pleasure, convenience to liberty, and a pleasant temperature to the deathly inner consuming fire.”