# Evolution of the Thermometer/Chapter 5

V. Thermometers of Réaumur, Celsius, and Others.
Thermometers for a special and limited use were manufactured about 1727 by John Fowler, Swithin's alley, near the Royal Exchange, London; these were adapted to the cultivation of hot-house plants, being graduated to indicate degrees most "kindly" to given plants. The instruments varied in length from 18 inches to 4 feet, and the stems were marked ​from freezing-point of water to 90° a temperature equal to that of warm water capable of being endured by the hand held still, certainly a very vague standard but perhaps sufficiently accurate for vegetable life.
The proper temperatures for specified plants were as follows, the degrees being those given by Hales.
Hales' Table. :
| Melon thistles | 31 |
| Ananas | 29 |
| Piamento | 26 |
| Euphorbium | 24 |
| Cereus | 21 |
| Aloes | 19 |
| Indian figs | 16 |
| Ficoides | 14 |
| Oranges | 12 |
| Mistles | 9 |
| (Phil. Trans., Apr.-June, 1727.) ||
These instruments were used by the eminent botanist, Rev. Stephen Hales, who describes them in his "Vegetable Statics," 1727 (p. 61). Dr. Hales remarks that "64 of these degrees is nearly equal to the heat of the blood of animals," which he determined by placing the "ball of the thermometer in the blood of an expiring ox." The "temperate" point was about 18 of these degrees.
​Réaumur, who next sought to improve the thermometer, was one of the most popular savants in France; his position in the world of science as well as in that of society, was far more conspicuous than that of the humble artisan Fahrenheit, and his aristocratic station is evidenced by his full name: René Antoine Ferchault, Seigneur de Réaumur, des Angles et de la Bermondière. He early became a member of the French Academy of Sciences, and for more than fifty years assiduously cultivated the sciences; his studies embraced the industrial arts, the physical and the natural sciences, and his publications were very numerous. In the Memoirs of the Academy of Sciences for 1731 he published a long paper entitled: "Rules for the Construction of Thermometers with Comparable Scales," which in its verbosity and prolixity contrasts strongly with Fahrenheit's conciseness.
Réaumur, like so many Frenchmen, completely ignored the thermometrical labors of the German, and rejected quicksilver, owing to its small coefficient of expansion; he sought by means of dilute alcohol to arrange a scale so that a definite change in volume would correspond to a definite rise or fall in temperature. ​He adopted a single fixed point, the freezing-point of water, a constant more difficult to determine accurately than the melting-point of ice; he ascertained that alcohol diluted with one-fifth water expanded from 1000 to 1080 volumes between the freezing- and boiling-points of water, and so he took zero for the lower and 80 for the higher temperature, dividing the intervening space into 80 parts.
Réaumur showed much ingenuity in his experimental work, but in his theoretical conclusions he made serious errors; he believed erroneously that he obtained the temperature of boiling water by immersing the unsealed alcohol tube in boiling water, and he ignored the influence of air-pressure, although Fahrenheit's experiments were generally known. For these and other reasons his thermometers were not satisfactory; with bulbs three to four inches in diameter the instruments were too large for standardizing smaller ones, and attempts to transfer Réaumur's scale to mercury thermometers led to confusion. Lambert, writing in 1779, gives for Réaumur three scales: first, that intended by him, second, the so-called Réaumur scale applied to mercury thermometers, and third, the scale actually obtained by ​the savant, which did not, however, agree with that proposed by him.
Thermometers made after Réaumur's plans were constructed by the Abbé Nollet (1732), by Tobias Mayer, by Boissier de Sauvages, and by Brisson; the latter proposed quite properly to use the melting-point of ice rather than the freezing-point of water as the lower fixed point, and he took the heat of the human body for a second fixed point making it equal to 32½ degrees Brisson.
The Abbé Soumille constructed a thermometer like that of Réaumur, but in four sections; in the first section the temperature of melting ice was placed at the top of the tube, and the tube was graduated downward to−20 at the bottom; the second section began where the first ended, the temperature of melting ice being at the bottom of the tube and the scale extending to +20; the third section ran from 20 to 40 and the fourth to 60. The spaces between degrees were an inch long admitting of fine subdivision. (Hist. Acad. Sci., Paris, 1770, p. 112.)
Réaumur's methods were severely criticized by De Luc in his researches on the modifications of the atmosphere; on the other hand ​Lambert makes the caustic remark: "Had De Luc written a work four times as small, he might have said four times as much as he did say."
Shortly after Réaumur's publication Joseph Nicolas de l'Isle, professor of astronomy in St. Petersburg, devised a thermometer on the same principles, but adopted as the point of departure the temperature of boiling water, calling it zero, and adjusting the scale so that the freezing-point of water equaled 150 degrees. This instrument was not much used outside of Russia.
In 1741, Jacques Barthélémi Micheli du Crest, of Switzerland, an army officer, presented many arguments against the scale of Réaumur; he used mercury only for calibrating tubes and rejected it as a thermometrical liquid, owing to the great difficulty of purifying it, preferring alcohol that had stood the gunpowder test. He took as one fixed point the "temperature of the terrestrial globe," as observed in the cellar of the Paris observatory, 84 feet deep, and as the second fixed point the boiling-point of water; the interval he divided into 100 degrees. The degrees in this scale nearly coincide with those of Réaumur. The ​thermometer of Du Crest was commonly used in northern Switzerland, and only a few years ago aged people often cited air-temperatures in Du Crest degrees.
In 1749 Du Crest was condemned for political reasons to lifelong imprisonment, and during the seventeen years that he spent in the fortress at Aargau he published several papers on meteorology; he died in 1766.
Anders Celsius, professor of astronomy at Upsala, proposed in 1742 a scale with zero at the boiling-point of water (the barometer at 25 inches, 3 lines), and with 100 at the temperature of melting ice. Celsius's scale is sometimes confounded with the French centesimal scale now in use, through neglect to remember the inversion. The change to the modern centigrade was made by two scientists independently, Christin, of Lyons, and Märten Strömer, of Upsala. The Lyons savant worked out the same plan as Celsius independently and published his results in the local papers in 1743. He disregarded the barometric pressure but in other respects his thermometer did not differ from the mercury centigrade thermometer of France; Christin's instrument was known as the thermometer of Lyons.
​Seven years later Strömer, a colleague of Celsius, also inverted the scale and his thermometer was used in meteorological observations at Upsala from 1750.
The centesimal division of the scale between the freezing-point and the boiling-point has been claimed for Linnaeus, the eminent Swedish botanist. In 1844, Arago made a communication to the French Academy of Sciences, quoting a private letter of Linnaeus, who wrote that he was the first to construct a thermometer with the centesimal division of the scale between the freezing-point and the boiling-point of water, for use in a green-house. Unfortunately the date of Linnaeus' letter is not given. (Compte rendu, 18, 1063.)
I have now completed the task undertaken, viz., to sketch impartially the history of the evolution of the thermometer from its first beginnings in Italy, through its crude early forms down to the three standards now commonly used in all civilized lands. It is interesting to note: First, that no nation makes popular use of the thermometer designed by its own citizen. The instrument constructed by the German Fahrenheit in the Netherlands is used almost exclusively in English-speaking lands; ​that invented by the Frenchman Réaumer finds no credit in France, but is popular in Germany; and that of Celsius, the Swede, modified by Christin, of Lyons, is used chiefly in France, Belgium, and Switzerland.
Secondly, no one of the thermometers now in use has exactly the scale originally devised by the person whose name is attached to it, later and more perfect methods of manufacture having modified the primary form.
The following table of thirty-five thermometer scales has been compiled from many sources, including the tables of Dr. Martine and of Van Swinden.