Degree Fahrenheit

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Categories: Units of temperature | Imperial units | Customary units in the United States

"Fahrenheit" redirects here. For other uses, see Fahrenheit (disambiguation).

Fahrenheit is a temperature scale named after the German physicist Gabriel Fahrenheit (1686–1736), who proposed it in 1724.

In this scale, the freezing point of water is 32 degrees (this is written "32 °F"), and the boiling point is 212 degrees Fahrenheit, placing the boiling and melting points of water 180 degrees apart. Thus the unit of this scale, a degree Fahrenheit, is 5/9ths of a kelvin (which is a degree Celsius), and minus 40 degrees Fahrenheit is equal to minus 40 degrees Celsius.

Degree Fahrenheit
Kelvin	[K] = ([°F] + 459.67) · 5/9	[°F] = [K] · 9/5 − 459.67
Celsius	[°C] = ([°F] − 32) · 5/9	[°F] = [°C] · 9/5 + 32
Rankine	[°Ra] = [°F] + 459.67	[°F] = [°Ra] − 459.67
Réaumur	[°Ré] = ([°F] − 32) · 4/9	[°F] = [°Ré] · 9/4 + 32
Newton	[°N] = ([°F] − 32) · 11/60	[°F] = [°N] · 60/11 + 32
Rømer	[°Rø] = ([°F] − 32) · 7/24 + 7.5	[°F] = ([°Rø] − 7.5) · 24/7 + 32
Delisle	[°De] = (212 − [°F]) · 5/6	[°F] = 212 − [°De] · 6/5

1 History
2 Usage
3 Curiosities
4 External links

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History

There are several competing versions of the story of how Fahrenheit came to devise his temperature scale. One states that Fahrenheit established the zero (0 °F) and 100 °F points on his scale by recording the lowest outdoor temperatures he could measure, and his own body temperature. He took as his zero point the lowest temperature he measured in the harsh winter of 1708 thru 1709 in his home town of Danzig (-17.8 °C). (He was later able to reach this temperature under laboratory conditions using a mixture of ice, ammonium chloride and water.) Fahrenheit wanted to avoid the negative temperatures which Ole Rømer's scale had produced in every day use. Fahrenheit fixed his own body temperature as 100 °F (normal body temperature is 98 °F, suggesting that Fahrenheit was suffering a fever when he conducted his experiments or that his thermometer was not very accurate), and divided his original scale into twelve divisions; later dividing each of these into 8 equal subdivisions produced a scale of 96 degrees. Fahrenheit noted that his scale placed the freezing point of water at 32 °F and the boiling point at 212 °F, a neat 180 degrees apart.

Another holds that Fahrenheit established the zero of his scale (0 °F) as the temperature at which an equal mixture of ice and salt melts (some say he took that fixed mixture of ice and salt that produced the lowest temperature); and ninety-six degrees as the temperature of blood (he initially used horse blood to calibrate his scale). Initially, his scale had only contained 12 equal subdivisions, but then later he subdivided each division into 8 equal degrees ending up with 96. He then observed that plain water would freeze at 32 degrees and boil at 212 degrees.

A third well-known version of the story, as described in the popular physics television series The Mechanical Universe, holds that Fahrenheit simply adopted Rømer's scale, at which water freezes at 7.5 degrees, and multiplied each value by 4 in order to eliminate the fractions and increase the granularity of the scale (giving 30 and 240 degrees). He then re-calibrated his scale between the freezing point of water and normal human body temperature (which he took to be 96 degrees); the freezing point of water was adjusted to 32 degrees so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).

His measurements were not entirely accurate, though; by his original scale, the actual freezing and boiling points would have been noticeably different from 32 °F and 212 °F. Some time after his death, it was decided to recalibrate the scale with 32 °F and 212 °F as the exact freezing and boiling points of plain water. This resulted in the healthy human body temperature being 98.6 °F rather than 96 °F. That change was made to easily convert from Celsius to Fahrenheit and vice versa, with a simple formula. This change could also explain why the body temperature once taken as 100 °F by Fahrenheit is today taken by many as 98.6 °F—because that is a nice, round 37 °C—but more accurately yet in the neighborhood of 98.2 °F.

A fourth, not so well-known version of the origin of the Fahrenheit scale depends on Fahrenheit himself being a Freemason (of which there is no definitive evidence). In Freemasonry, there are 32 degrees of enlightenment, 32 being the highest. The use of the 'degree' as well is said to have been derived from the degrees of masonry. This may well be coincidence, but there is no conclusive evidence to the contrary, so the thought persists.

In addition, a more humorous but very possible rumor regarding just how Fahrenheit chose his higher temperature involves a not-so-scientific approach to measuring the temperature of a human body. Supposedly, having no human volunteers from which to take his measurement, and not wanting to test it on himself (possibly for lack of an average between several bodies), he decided that the anal temperature of a common pig would closely match the internal body temperature of a human. He proceeded to mark the temperatures of several swine on a mercury tube, found the average, and claimed it to be correct. While the idea of a fairly esteemed scientist taking such a chance with measurement is questionable, given the fact that the body temperature of a pig is very close to that of a human, the logic behind this hasty decision would at least be fairly well placed. It is possible that, in a rush to meet a deadline determined by a boast or otherwise, it was his only option. This is, of course, only a rumor, though it could also account for the slight inaccuracy of Fahrenheit's 100 degree mark being the supposed internal body temperature of a human.

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Usage

The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in most English-speaking countries until the 1960s. In the late 1960s and 1970s the Celsius (formerly centigrade) scale was phased-in by governments as part of the standardizing process of metrication. However, despite official attempts to displace it, Fahrenheit remains in use for everyday, non-scientific temperature measurement by the general population of many English-speaking countries out of habit.

Fahrenheit supporters claim this is due to Fahrenheit's user-friendliness. The unit of measure, being only 5/9 the size of the Celsius degree, permits more precise communication of measurements without resorting to fractional degrees. Also, the ambient air temperature in most inhabited regions of the world tends not to go far beyond the range of 0 °F to 100 °F: therefore, the Fahrenheit scale would reflect the perceived ambient temperatures, following 10-degree bands that emerge in the Fahrenheit system:

10s Deep Frost.
20s Light Frost.
30s Cold. Close to freezing.
40s Cold. Heavy clothing needed.
50s Very cool. Moderate Clothing required.
60s Cool. Light clothing.
70s Comfortable. Summer clothing.
80s Warm. Bearable. Minimal clothing.
90s Hot.
100s Very hot. Take precautions against overheating.

However, such a correlation is largely the result of habit: in the same way, Celsius supporters might indicate that 0-10 °C indicates cold, 10-20 °C mild, 20-30 °C warm and 30-40 °C hot, with the minus sign indicating frost.

In the United States and Jamaica, where metrication has encountered greater resistance from industry and consumers, the Fahrenheit system continues to be very widely used for this purpose. Similarly, in parts of the United Kingdom, both systems are used; Fahrenheit is still used by older generations for everyday measurement of higher temperatures, while lower temperatures are more often measured in degrees Celsius. Younger generations tend to follow the same routine. In Canada, although the media is required to report temperatures in degrees Celsius, many older Canadians still describe temperatures in degrees Fahrenheit.

In popular medicine too, it is well known that the normal body temperature in Fahrenheit is 98.6 degrees, and easy to remember that a temperature in excess of 100 degrees Fahrenheit requires medical attention.

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