Fahrenheit, Daniel Gabriel

views updated May 29 2018

Fahrenheit, Daniel Gabriel

(b. Danzig [Gdansk], Poland, 24 May 1686; d. The Hague, Natherlands, 16 September 1736)

experimental physics.

Fahrenheit was the scion of a wealthy merchant family that had come to Danzig from Königsberg in the middle of the serventeenth century. His father, Daniel, married Concordia Schumann, the daughter of Danzig wholesaler. From this union there were five children, three girls and two boys, of whom Daniel was the eldest.

In 1701 Fahrenheit’s parents died suddenly, and his guardian sent him to Amsterdam to learn business. It was there, apparently, the Fahrenheit first became acquainted with, and then fascinated by, the rather specialized and small but rapidly growing business of making scientific instruments. About 1707 he began his years of wandering, during which he acquired the techniques of his trade by observing the practices of other scientists and instrument makers. He traveled throughout Germany, visiting his native city of Danzig as well as Berlin, Halle, Leipzig, and Dresden. He met Olaus Roemer in Copenhagen in 1708, and in 1715 he entered into correspondence with Leibniz about a clock for determining longitude at sea. In 1714 Christian von Wolff published a description of one of Fahrenheit’s early thermometers in the Acta eruditorum. Fahrenheit returned to Amsterdam in 1717 and established himself as a maker of scientific instruments. There he became acquainted with three of the greatest Dutch scientists of his era: W. J. ’sGravesande, Hermann Boerhaave, and Pieter van Musschenbroek. In 1724 he was admitted to the Royal Society, and in the same year he published in the Philosophical Transactions his only scientific writings, five brief articles in Latin. Just before his death in 1736, Fahrenheit took out a patent on a pumping device that he hoped would be useful in draining Dutch polders.

Fahrenheit’s most significant achievement was his development of the standard thermometric scale that bears his name. Nearly a century had passed since the construction of the first primitive thermometers, and although many of the basic problems of thermometry had been solved, no standard thermometric scale had been developed that would allow scientists in different locations to compare temperatures. About 1701 Olaus Roemeṙ had constructed a spirit thermometer based upon two universal fiducial points. The upper fixed point, determined by the temperature of boiling water, was labeled 60°; the lower fixed point, determined by the temperature of melting ice, was set at 7–1/2°. This latter, seemingly arbitrary, number was chosen to allow exactly 1/8 of the entire scale to stand below the freezing point. Since 00 on the Roemer scale approximated the temperature of an ice and salt mixture (which was widely considered to be at the coldest possible temperature), all readings on Roemer’s thermometer were assumed to be positive.

Roemer did not publish anything about his thermometer, and its existence was unknown to most of his contemporaries except Fahrenheit, who thought mistakenly that his own thermometric scale was patterned after Roemer’s. In 1708, while visiting Roemer, Fahrenheit watched the Danish astronomer as he graduated several thermometers. These particular instruments were being graduated to a scale of 22–1/2°, or 3/8 of Roemer’s standard scale of 60°. Since most of the scale would then be in the temperate range, it is probable that Roemer was designing them for meteorological purposes. In a letter addressed to Boerhaave, Fahrenheit gave the following description of Roemer’s procedure.

I found that he had stood several thermometers in water and ice, and later he dipped these in warm water, which was at blood-heat [welches blutwarm war], and after he had marked these two limits on all the thermometers, half the distance between them was added below the point in the vessel with ice, and the whole distance divided into 22–1/2 parts, beginning with 0 at the bottom then 7–1/2 for the point in the vessel with ice and 22–1/2 degrees for that at blood-heat.1

The problem with Fahrenheit’s account is that he took Roemer’s “blood-warm” (22–1/2°) to be a primary fiducial point, fixed quite literally at the temperature of the human blood. In fact, 22–1/2° on the Roemer scale is considerably below body temperature (by about 15° on the modern Fahrenheit thermometer). Furthermore, Roemer used boiling water (set at 60°), not blood temperature, as his upper fixed point. The simplest explanation for Fahrenheit’s misunderstanding of the Roemer scale seems to lie in the ambiguity of the term “blood-warm.” It can mean either a tepid heat or the exact temperature of the human blood.2 Roemer probably intended to convey the former meaning, and Fahrenheit obviously understood the latter one.

When Fahrenheit began producing thermometers of his own, he graduated them after what he believed were Roemer’s methods. The upper fixed point (labeled 22–1/2°) was determined by placing the bulb of the thermometer in the mouth or armpit of a healthy male.3 The lower fixed point (labeled 7–1/2°) was determined by an ice and water mixture. In addition, Fahrenheit divided each degree into four parts, so that the upper point became 90° and the lower one 30°. Later (in 1717) he moved the upper point to 96° and the lower one to 32° in order to eliminate “inconvenient and awkward fractions.”4

In an article on the boiling points of various liquids, Fahrenheit reported that the boiling temperature of water was 212° on his thermometric scale. This figure was actually several degrees higher than it should have been. After Fahrenheit’s death it became standard practice to graduate Fahrenheit thermometers with the boiling point of water (set at 212°) as the upper fixed point. As a result, normal body temperature became 98.6° instead of Fahrenheit’s 96°. This variant of the Fahrenheit scale became standard throughout Holland and Britain. Today it is used for meteorological purposes in most English-speaking countries.

Fahrenheit knew that the boiling temperature of water varied with the atmospheric pressure, and on this Principle he constructed a hypsometric thermometer that enabled one to determine the atmospheric Pressure directly from a reading of the boiling point of water. He also invented a hydrometer that became a model for subsequent developments.

In the early eighteenth century, it was not at all unusual for a person without formal scientific training to be admitted to the Royal Society. Makers of scientific instruments could be particularly valuable members because they often operated on the farthest frontiers of scientific knowledge, defining universal constants on which to scale their instruments and isolating the variables that affected their operation. In order to make reliable instruments that would be useful to the scientific community as a whole, Fahrenheit was obliged to concern himself with a wide variety of scientific Problems: measuring the expansion of glass, assessing the thermometric behavior of mercury and alcohol, describing the effects of atmospheric pressure on the boiling points of liquids and establishing the densities of various substances. His direct contributions, it is true, were small, but in raising appreciably the level of precision that was obtainable in many scientific observations, Fahrenheit affected profoundly the course of experimental physics in the eighteenth century.


1. Quoted from W.E. Knowles middleton, A History of the Thermometer and Its Use in Meteorology (Baltimore, 1966), p. 71.

2. J. U. W. Grimm’s Deutsches Wörterbuch gives “tepid”as the definition of blutwarm. Blutwärm (“blood-heat”) is defined as the temperature of the blood. Francis Hauksbee, in his Physico-Mechanical Experiments, wrote; “I caus’s some eater to be heated about Blood-warm”(quoted in the Oxford English Dictionary, I,933). The French translation (Paris, 1754, I,385) reads “hellip; je fis chauffer de I’eau jusqu’àa ce qu’elle fôt un peu plus que tiéd.
(ldquo;I caused some water to be heated until it was a little more than tepid.”)

3. It seems curious that Fathrenheit should have stipulated that of the subject be a man. Perhaps this is owing to some remanant of the once widely held notion that women naturally have a lower body temperature than men. (See Jacques Roger, Les sciences de la die dans la penséee francaise du XVIII e; siécle [Paris 1963], pp. 84 ff.)

4. Middleton, loc. cit.


I. Original Works. All of Fahrenheit’ published works appeared in the Philosophical Transactions of the Royal Society, 33 (1724): “Experimenta Circa gradum caloris liquorum nonnullorum ebullientium institua,” pp. 1–3;“Experimenta Observationes de congelatione aquae in vacuo factae,” pp. 78–84; “Materium quarundum gravitates specificae diversis temporibus ad varios scopos explorratae” Pp.114–141; “Araemetri novi descript,” pp. 179–180. These are translated into German in Ostwalds Klassiker der Exacten Wissenschaften, no. 57 (Leipzig, 1954), pp. 3–18.

II. Secondary Literature. There is an enormous quantity of literature on Fahrenheit. The following list is limited to recent articles of importance: Florian Cajori, “Note on the Fahrenheit Scale” in Isis, 4 (1921), 17–22; Ernst Cohen and W. A. T. Cohen-De Meester, “Daniel Gabriel Fahrenheit,” in verhandeligen der Konenklijke akademie uan wetenschappen, sec. 1, 16 no. 2 (1937), 1–37; N. Ernest Dorsey, “Fahrenheit and Roemer,” in Journal of the Washington Academy of Sciences, 36, no. 11 (1946),361–372;and W. E. knowles Middleton, A History of the Thermometer and Its Use in Meterorology (Baltimore, 1966), pp. 66–79.

J. B. Gough

Fahrenheit, Daniel Gabriel (1686-1736)

views updated May 29 2018

Fahrenheit, Daniel Gabriel (1686-1736)

Dutch physicist

Daniel Fahrenheit invented the first truly accurate thermometer using mercury instead of alcohol and water mixtures. In the laboratory, he used his invention to develop the first temperature scale precise enough to become a worldwide standard.

The eldest of five children born to a wealthy merchant, Fahrenheit was born in Danzig (Gdansk), Poland. When he was fifteen his parents died suddenly, and he was sent to Amsterdam to study business. Instead of pursuing this trade, Fahrenheit became interested in the growing field of scientific instruments and their construction. Sometime around 1707, Fahrenheit began to wander the European countryside, visiting instrument makers in Germany, Denmark, and elsewhere, learning their skills. He began constructing his own thermometers in 1714, and it was in these that he used mercury for the first time.

Previous thermometers, such as those constructed by Galileo and Guillaume Amontons, used combinations of alcohol and water; as the temperature rose, the alcohol would expand and the level within the thermometer would increase. These thermometers were not particularly accurate, however, since they were too easily thrown off by changing air pressure. The key to Fahrenheit's thermometer was a new method for cleaning mercury that enabled it to rise and fall within the tube without sticking to the sides. Mercury was an ideal substance for reading temperatures since it expanded at a more constant rate than alcohol and is able to be read at much higher and lower temperatures.

The next important step in the development of a standard temperature scale was the choosing of fixed high and low points. It was common in the early eighteenth century to choose as the high point the temperature of the body, and as the low point the freezing temperature of an ice-and-salt mixture, then believed to be the coldest temperature achievable in the laboratory. These were the points chosen by Claus Roemer, a German scientist whom Fahrenheit visited in 1701. Roemer's scale placed blood temperature at 22.5°F and the freezing point of pure water at 7.5°F. When Fahrenheit graduated his own scale he emulated Roemer's fixed points; however, with the improved accuracy of a mercury thermometer, he was able to split each degree into four, making the freezing point of water 30°F and the temperature of the human body 90°F. In 1717, he moved his points to 32°F and 96°F in order to eliminate fractions.

These points remained fixed for several years, during which time Fahrenheit performed extensive research on the freezing and boiling points of water. He found that the boiling point was constant, but that it could be changed as atmospheric pressure was decreased (such as by increasing elevation to many thousand feet above sea level). He placed the boiling point of water at 212°F, a figure that was actually several degrees too low. After Fahrenheit's death scientists chose to adopt this temperature as the boiling point of water and to shift the scale slightly to accommodate the change. With 212°F as the boiling point of water and 32°F as the freezing point, the new normal temperature for the human body became 98.6°F.

In 1742, Fahrenheit was admitted to the British Royal Society despite having had no formal scientific training and having published just one collection of research papers.

See also Temperature and temperature scales

Fahrenheit, Daniel Gabriel

views updated May 18 2018

Fahrenheit, Daniel Gabriel


Observations are the heart of the scientific method, but human perception is faulty when it comes to observing "absolutes." That is, one may be able to say that this liquid is hotter than that liquid, but not by how much, nor their exact temperatures. For science to be meaningful and its results reproducible, some external mechanism for making (and comparing) measurements that can be used by scientists must exist.

Daniel Gabriel Fahrenheit was a German physicist living in the Netherlands in the early eighteenth century. Like many of his contemporaries, he was interested in a great many phenomena, but the one phenomenon that really seized his attention was the boiling of liquids. Fahrenheit discovered that pure liquids boil at fixed temperatures, which are not influenced by the continued application of heat. He described his reaction to this discovery in his Philosophical Transactions (1724): "I was at once inflamed with a great desire to make for myself a thermometer of the same sort [a water-based thermometer], so that I might with my own eyes perceive this beautiful phenomenon of nature, and be convinced of the truth of the experiment."

Fahrenheit could not make a "thermometer of the same sort," despite repeated attempts. The type of thermometer that he was trying to make used water, open to the atmosphere, as the fluid of expansion. His original thermometers were thus sensitive to air pressure, and acted as both barometers and thermometers at the same time.

Fahrenheit subsequently recognized that both alcohol and mercury expanded with heat. He built closed bulb thermometers that contained alcohol (1709) and mercury (1714), thereby inventing the modern thermometer. With these instruments, he was able to make much more accurate and more consistent measurements of temperature. And he discovered, among other things, that water can be supercooled (cooled below its normal freezing point), and that the boiling point of a liquid is not a constant, but is a function of atmospheric pressure. Fahrenheit used supercooled water (from a mixture of water, ice, and sal ammoniac [ammonium chloride]) to establish his zero point, and his own body temperature to establish what would be 100 degrees. (Of course, we now gauge normal body temperature to be 98.6°F.) Fahrenheit's thermometers were the first to enable accurate and reproducible measurements of temperature.

Until the 1970s, the Fahrenheit scale was in common use in all English-speaking countries. Since then, the Celsius scale has been adopted by most countries (not including the United States).

see also Temperature.

Todd W. Whitcombe


Asimov, Isaac (1989). Asimov's Chronology of Science and Discovery. New York: Harper & Row.

Internet Resources

Fahrenheit, Daniel Gabriel. Philosophical Transactions, translated. Available from <http://webserver.lemoyne.edu/faculty/giunta>.

Gabriel Daniel Fahrenheit

views updated May 14 2018

Gabriel Daniel Fahrenheit

The German instrument maker Gabriel Daniel Fahrenheit (1686-1736) made the first reliable thermometers. The temperature scale he originated is named after him.

Born in Danzig on May 14, 1686, Gabriel Fahrenheit was the son of a well-to-do merchant. He lost both parents on the same day, Aug. 14, 1701, and was thereafter apprenticed to a shopkeeper in Amsterdam. After completing a term of 4 years there, he turned to physics and became an instrument maker and glassblower. Although he lived in Amsterdam most of his life, he traveled widely and spent considerable time in England, where he became a member of the Royal Society.

Fahrenheit completed his first two thermometers by 1714. They contained alcohol and agreed exactly in readings. The scale which was to bear Fahrenheit's name had not yet been calibrated, and many different scales were tried before he settled on one. He soon decided to replace the alcohol with mercury and completed a series of investigations based on the work of G. Amontons, in which he determined the boiling point of water and other liquids and studied the expansion properties of mercury. These experiments led to the discovery that the boiling point of water varied with changes in atmospheric pressure. Fahrenheit also discovered the phenomenon of supercooling of water, that is, cooling water to below its normal freezing point without converting it to ice.

Taking all of these factors into consideration, Fahrenheit was led to doubt the reliability of the freezing and boiling points of water and finally settled on a temperature scale ranging from 0 to 212. In 1724, announcing his method of making thermometers in the Philosophical Transactions of the Royal Society, he wrote concerning his scale, " … degree 48, which in my thermometers holds the middle place between the limit of the most intense cold obtainable artificially in a mixture of water, of ice, and of sal ammoniac or even of sea salt, and the limit of heat which is found in the blood of a healthy man." (It has been suggested that the 96-degree range was chosen simply for the convenience of that number when laying off the scale by halving spaces on the thermometer stem.) Thus, finding the temperatures of the human body and of his freezing mixture to be reliable parameters, he set 0 as the temperature of the mixture; 32 as the temperature of water and ice; and 212, a point selected by chance, as about the boiling point of water.

Fahrenheit's thermometers were highly esteemed. He used mercury successfully because of his technique for cleaning it, and he introduced the use of cylindrical bulbs instead of spherical ones. However, his detailed technique for making thermometers was not disclosed for some 18 years, since it was a trade secret. Among the other instruments which he devised were a constant-weight hydrometer of excellent design and a "thermobarometer" for estimating barometric pressure by determining the boiling point of water.

On Sept. 16, 1736, Fahrenheit died, unmarried, in the Netherlands, presumably in The Hague, where he was buried.

Further Reading

Henry Lipson, The Great Experiments in Physics (1968), includes a chapter on heat with reference to Fahrenheit. For background and additional material on Fahrenheit see Florian Cajori, A History of Physics (1899; rev. ed. 1929); Max von Laue, History of Physics (1947; trans. 1950); and Allen L. King, Thermophysics (1962). □

Fahrenheit, Gabriel Daniel

views updated May 29 2018

Fahrenheit, Gabriel Daniel (1686–1736) German physicist and instrument-maker. He invented the alcohol thermometer (1709), the first mercury thermometer (1714) and devised the Fahrenheit temperature scale. He also showed the boiling points of liquids vary with changes in pressure and that water can remain liquid below its freezing point.

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