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 Roemer? 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.

NOTES

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.

BIBLIOGRAPHY

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