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Hot Stuff: The Story of Fahrenheit and Celsius

Hot Stuff: The Story of Fahrenheit and Celsius

Hot Stuff: The Story of Fahrenheit and Celsius

Every day, all over the world, people check temperature readings with no thought about where those numbers come from. Yet, before a few smart people found ways to accurately measure and grade it, temperature was largely each individual’s imprecise personal opinion. It was either hot or cold, freezing or roasting or somewhere in between. This imprecision caused problems: Apart from people dressing inappropriately for the weather, cooks burned food or undercooked it, pharmacists concocted useless or often dangerous medicines, and blacksmiths molded brittle swords. More seriously, sick patients died because doctors misjudged their temperature and misdiagnosed their illnesses.

All that changed, albeit gradually in the 18th century. If the 1700s are noted for anything, it’s the huge number of brilliant scientists it produced. Enthusiasts spouting all sorts of scientific and pseudo-scientific ideas proliferated. A few scientists were true geniuses; inventors and discoverers who contributed greatly to scientific advancement and so to the betterment of humanity. Two in particular stand out because of their groundbreaking work on temperature.

One was born to a German merchant family in Danzig (now Gdańsk, Poland) in 1686. His name is Daniel Gabriel Fahrenheit. He moved to the Dutch Republic as a teenager and lived there for the rest of his life. He died in 1736 at the age of 50 in The Hague. The other is Swedish astronomer Anders Celsius, who was born to a family of scientists in Uppsala, Sweden in 1701.

Though near contemporaries, each of these men separately devised similar instruments for measuring and grading temperature. Their portable inventions transformed most fields of science. The process of gauging temperature went from being annoyingly (and often, dangerously) haphazard to being reliably precise.

In 1712, Fahrenheit invented the mercury thermometer, by far the most accurate and reliable way of measuring temperature at that time. Versions of it were widely used until the mid-20th century, and some are still used today. Fahrenheit decided that the zero point (0°F) of his new instrument’s scale would the temperature at which a solution of ice, water and ammonium chloride froze.

He then set the melting point of ice at 32°F and calculated the temperature of the human body as 96°F. Future scientists extended this scale calculating the boiling point of water as 212°F – 180°F above its freezing point. They also calculated more accurately the human body’s normal temperature to be 98.6°F.

Fahrenheit’s scale was used worldwide for decades. It was the standard in most English-speaking countries until the1970s and is still the standard in the USA. Most other countries have now converted to the centigrade system, based on that devised by Anders Celsius.

Today’s Celsius system seems very logical, perhaps more logical than the Fahrenheit one. The freezing point of water is 0°C and the boiling point 100°C. It wasn’t always quite so logical, however. When Celsius devised it in 1742, the scale was the other way round – the boiling temperature of water was 0°C and the freezing point 100°C. He named his new system “centigrade” from the two Latin words “centi,” meaning one hundred, and “gradus,” meaning a step.

About a year later, apparently working independently of Celsius, the French physicist, Jean-Pierre Christin, developed a very similar centigrade system, but where 0° was the freezing point of water and 100° its boiling point. He also designed a mercury thermometer that used that scale.

The following year, Swedish botanist Carl Linnaeus commissioned a thermometer for use in his greenhouses, on which the scale was the same as on Christin’s device, (the reverse of the original Celsius scale). That same year, 1744, one could say that Anders Celsius’ own body temperature plummeted or soared, depending on which thermometer his doctor used. He died in his home in Uppsala at the age of 44. In homage to him, the system he devised and named centigrade is now universally known as Celsius.

Today, though most people check temperature regularly (if only to help them decide what to wear or if the oven is ready for the chicken), few ever give much thought to the two scientists who invented thermometers and their calibration systems. Most may now be electronic, but it’s not so long ago since they were hollow glass tubes containing mercury or alcohol – exactly the same instruments devised by Daniel Gabriel Fahrenheit and Anders Celsius over 300 years ago.