Origins of Celsius and FahrenheitDate: 03/31/2002 at 00:52:02 From: Maranda Martin Subject: Celsius and Fahrenheit Dr. Math, Who invented Celsius and Fahrenheit? Date: 03/31/2002 at 08:35:20 From: Doctor Sarah Subject: Re: Celsius and Fahrenheit Hi Maranda - thanks for writing to Dr. Math. Russ Rowlett's _How Many? A Dictionary of Units of Measurement_ is a good site for looking up this kind of information. Select D for degree Celsius and degree Fahrenheit. Here's what he says: degree Celsius a metric unit of temperature. The Celsius temperature scale is named for the Swedish astronomer and physicist Anders Celsius (1701-1744), who used a similar scale. The freezing point of water (at one atmosphere of pressure) was originally defined to be 0 degrees Celsius, while the boiling point is 100 degrees Celsius. Thus the Celsius degree is 1/100 of the difference between these two temperatures. (The scale actually used by Celsius was inverted, so that 0 degrees Celsius was the boiling point of water and 100 degrees Celsius the freezing point.) In the SI system, the Celsius scale is defined so that the temperature of the triple point of water (the temperature at which water can exist simultaneously in the gaseous, liquid, and solid states) is exactly 0.01 degrees Celsius, and the size of the degree is 1/273.16 of the difference between this temperature and absolute zero (the temperature at which all molecular motion ceases). For practical purposes this is equivalent to the original definition. degree Fahrenheit a traditional unit of temperature still used customarily in the United States. The unit was defined by the German physicist Daniel G. Fahrenheit (1686-1736), who also invented the mercury thermometer. Fahrenheit set 0 degrees at the coldest temperature he could conveniently achieve using an ice and salt mixture, and he intended to set 100 degrees at the temperature of the human body. (He was off a little there; normal temperature for humans is between 98 degrees Fahrenheit and 99 degrees Fahrenheit.) On this scale, the freezing point of water (at normal sea level atmospheric pressure) turned out to be about 32 degrees Fahrenheit and the boiling point about 212 degrees Fahrenheit. Eventually the scale was precisely defined by these two temperatures. 1 degree Fahrenheit equals 5/9 degrees Celsius, but in converting between scales we have to be careful to adjust the zero points as well. To convert a temperature in degrees Fahrenheit to the Celsius scale, we must first subtract 32 degrees and then multiply by 5/9. In the other direction, to convert a temperature in degrees Celsius to the Fahrenheit scale, we must first multiply by 9/5 and then add 32 degrees. The Celsius scale is now used everywhere outside the United States, so only Americans need to remember these formulas. - Doctor Sarah, The Math Forum http://mathforum.org/dr.math/ |
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