What’s the Temperature?

What do the numbers 0, 32, 273.15, and 491.67 have in common? They all tell the freezing point of water from liquid to solid, giving us four ways to say the same thing depending on where you are and what profession you are in. Water freezes at zero degrees Celsius or centigrade, 32 degrees Fahrenheit, 273.15 kelvin, and 491.67 degrees Rankine.

Most of the world’s citizens, and especially those who work in medicine and science, use the Celsius temperature scale and would say that 0 is the freezing point of water. But the Celsius scale, developed by Swedish scientist Anders Celsius in 1742, is only one way out of several that we have for measuring temperature. His system is today called Celsius after him or centigrade because it is based on a base ten scale. Centigrade, by the way, is a combination of two Latin words: centum –100 and gradus — steps, so centigrade is 100 steps.  It is simple and logical in that water freezes at 0 and boils at 100 degrees. Most home thermostats are set at a comfortable 22 or 23 degrees.

Some countries, however, such as the United States, Liberia, Cayman Islands, The Bahamas and a few others, use a system that is a few years older than Celsius’s based on a scale developed by Polish scientist Daniel Gabriel Fahrenheit around 1714. Fahrenheit had visited Danish astronomer Ole Roemer around 1701 in Denmark and learned that Roemer had come up with the idea of a scale for measuring temperature based on the freezing point and boiling point of water, which apparently was a fairly new idea at the time.

Ole Roemer was already a noted scientists who in 1676 had come up with a speed of light based on close observations of the movement of Jupiter’s moon Io. His findings determined that light had a speed of 226,663 km per second, lower that today’s calculated speed but a respectable calculation considering the technology he had available to him.

Since at that time there was no standard system in Europe from one country to another for measuring temperature, Fahrenheit felt that Roemer’s system of measuring temperature based on the “triple point of water”, that is the temperatures where it changes from solid to liquid to gas was as good as any being used at the time. This became an economic and well as a scientific venture in that Fahrenheit felt he could make and sell his thermometers all over Europe.

Fahrenheit seems to have set up his thermometer on a base 60 scale similar to Roemer’s. Base 60 was used to measure the circumference of a circle and used the term ‘degrees’ to measure increments of distance around a circle, a complete circle being 360 degrees. Fahrenheit chose to use degrees to measure temperature gradations on his thermometer and we still use the terminology today.

After several adjustments, by 1717, Fahrenheit’s scale went from the coldest temperature he could produce from a combination of water, ice, and salt, which he designated as zero degrees, to where water freezes which ran to 30 degrees on his scale. Then his scale went to 90 degrees which he determined to be the temperature of the human body, and then on to 210 degrees when water boiled. This made water to boil at 60 times 3 or 180 degrees hotter than the freezing temperature of water.  Later refinements set water freezing at 32 degrees, water boiling at 212 degrees, and the temperature of the human body at 98.6.

It is interesting that the base 60 scale Fahrenheit used goes back to the Babylonians who began using the system around 600 BC. Apparently, it was initially based on a rounded off number of days in the year, 360. The Babylonians also liked the numbers 60 and 360 because they can be divided by so many divisors. For example, 60 can be divided by 1, 2, 3, 5, 6, 12, 15, 20, 30, and 60. That is more than any other number up to 60. 6 times 60 degrees works well for 360-degree circles so the concept stuck.

Although, it may have seemed a bit awkward at first, but Fahrenheit’s thermometer became the standard in Europe for several years and, as stated before, is still in use in some countries. It seems, however, that Fahrenheits must have been a better scientist than a business man. His thermometer helped standardize temperature readings in various countries around the world, yet Fahrenheit died poor in 1736 at 50 years of age.

Apparently, not totally pleased with Fahrenheit’s base 60 thermometer, other scientists came up with different systems. One that gained some favor for a few years but is seldom used today was the thermometer developed by Rene’ Reaumur in 1730 that used a base 80 notation. Water froze at zero degrees and boiled at 80 degrees. Reaumur’s thermometer remained in use in some European countries into the early 20^th century.

It was in 1742 that Swedish scientist Anders Celsius came up with a new thermometer based on the decimal or base 10 system, a more intuitive system since people have ten fingers and ten toes. Celsius came from a scientific family and made several discoveries other than a new way to measure temperature. For example, he did extensive studies of aurora borealis or northern lights and determined that they were caused by Earth’s magnetic field, and he confirmed Isaac Newton’s hypothesis that the Earth is not perfectly round, but due to its rotation, is an oblate spheroid that bulges slightly at the equator and is flattened at the poles.

Although Celsius’s first thermometer made use of Ole Roemer’s idea of having the scale based on the freezing point and boiling point of water, it was not like the one in use today. In an effort to rectify the problem that water boils at different temperatures depending on altitude and air pressure, Celsius had his scale go from top to bottom with zero degrees at the boiling point of water and 100 degrees as the freezing point. It was an awkward arrangement, so, in order to make the scale more logical, in 1743 French scientist Jean Pierre Christin reversed the scale to read bottom to top with zero degrees as the freezing point of water and 100 degrees as the boiling point at sea level or one atmosphere of pressure. People living higher than sea level lower their boiling point temperature. For example, residents of Denver, Colorado at an altitude of 5279 feet or 1609 meters, can boil water at 95 degrees Celsius or 203 degrees Fahrenheit.

Today the Celsius thermometer is in use in most of the world. Its 0 to 100 scale is simple and easy to understand. Decimals are used when the temperature needs to be exact, as is the case with other thermometers. For example, the human body temperature in Fahrenheit is 98.6 but an even 37 in Celsius. A warm spring day in Fahrenheit is 65 degrees or 18.3 in Celsius.

There was an attempt some years ago by the United States Congress to change the temperature and distance measurement systems in America to be more like the rest of the world. Instead of yards and miles, the system would be meters and kilometers and instead of the Fahrenheit scale, the country would use the Celsius or centigrade scale. But many people in America were content with the old systems and did not see a need to change. The medical and scientific communities, however, have always used the metric and Celsius systems and continue to do so.

It is interesting that the origin of inches, feet and yards is somewhat obscure and probably based on body parts. For example, the inch is probably based on the length if the last joint of the index finger. The foot is probably based on the length of some ancient person’s foot. A yard might have been the distance from one’s nose to the tip of the fingers. The only old measurement we are sure of is the cubit, which is the distance from the elbow to the tip of the fingers, which works out to be around 18 inches or 45 centimeters. It was the primary measurement used in the building of the Egyptian pyramids. The word cubit is based on the Latin word cubitum which means elbow.

The meter, on the other hand has a definite length. It was established by the French government in 1791 as one-ten millionth of the distance from the equator to the north pole, making the circumference of the Earth 40,000 kilometers from pole to pole. This measurement is very close to today’s measurement of 40,075.017 km or 24,901.46 miles at the equator.

Although Celsius and Fahrenheit cover most of the temperatures we encounter on a day- to-day basis, since the early 1800s when physicists and astronomers began to be concerned about temperatures beyond the bounds of Earth, it was noted that these two systems had their limitations, especially in determining the cold temperatures found several miles into space. In the 1840s, this need prompted Scotland’s University of Glasgow scientists William Thomson, who later was given the title Lord Kelvin, to work on a new system.

Thomson based his system on the Celsius scale but took the lower end down to Absolute Zero, the point at which all atomic and molecular movement stops except at the quantum level. In experiments Thomson did in 1848, in which a volume of gas was heated and cooled and its temperature carefully measured, Thomson determined that a theoretical absolute zero would be minus 273 degrees Celsius. Thomson’s theoretical zero proved to be extremely accurate for the methods and equipment used in his day. Absolute zero today is determined to be 273.15 degrees Celsius and is designated zero kelvin.

The idea of extremely cold temperatures goes back a few centuries. Seventeenth century chemist Robert Boyle was one of the first to propose that temperatures several degrees below the freezing point of water could be achieved. Several scientists around that time were trying to devise a better thermometer and the one he devised in 1650 was a bit more accurate than others. However, his idea of using the freezing point of aniseed oil as zero degrees never caught on. Boyle’s thermometer became another one in a long line of thermometers that failed to win long-term universal approval.

What Lord Kelvin did for the Celsius scale, a colleague of his at the University of Glasgow, William Rankine, in 1859, did for the Fahrenheit scale. He ran the scale from the freezing point of water at 32 degrees down to absolute zero and determined it to be minus 459.67 degrees Fahrenheit. Zero degrees Fahrenheit came to be called zero R. The scale is not popular today, but is occasionally used in countries that have not switched to the Celsius scale such as the United States.

So now we have the two major scales used in most of the world, Celsius and Fahrenheit and the extensions of them that go to the theoretical Absolute Zero. Although scientists have gotten to within a fraction of a degree to absolute zero, it might never be actually achieved since the containers used to hold the cooled gases will always give off a small amount of heat. Recent experiments using super cooled magnetized gases have achieved temperatures near absolute zero and the quest continues.

For millennia, people have used heat from fire to cook and we learned to create intense heat to melt metal into tools and weapons. Then a few years ago scientists discovered new ways to use low temperatures as well. For example, in 1911 Dutch physicist Heike Kamerlingh Onnes discovered that lowering the temperature of some metals to 30 k or minus 243.15 degrees Celsius caused them to become superconductors, a state in which electrical current flows with little friction interference. In our electrical world, superconductivity is becoming very important.

Gases can also be cooled enough to go through a phase change. Hydrogen, helium, and oxygen, for example, become liquids when cooled to extremely low temperatures. Hydrogen becomes a liquid at 20.28 k, or minus 252.87 degrees Celsius, or minus 423.17 degrees Fahrenheit. Helium must go down to 4.15 k, or minus 269 Celsius, or 452.20 degrees Fahrenheit. Oxygen becomes a liquid at 90.15 k, or minus 183 degrees Celsius, or minus 297 degrees Fahrenheit. Today these liquids are used extensively as rocket fuels and liquid helium is used to cool down the superconducting magnets in magnetic resonance machines (MRI).

So, the next time someone asks you, “What’s the temperature?”, be mindful of what country you are in and of the persons’ profession. A physicist in France will want a temperature in Celsius or kelvin while a politician in America will first want your vote and then his or her temperature in Fahrenheit.

Ted McCormack