RENE ANTOINE FERCHAULT DE REAUMUR, (1683-1757), the eldest son of a French nobleman, was born on 28th February 1683 at La Rochelle and received his early education there. He was taught philosophy in the Jesuits' college at Poitiers, and in 1699, when "hardly seventeen, but already possessed of the prudence of a grown man," went to Bourges to study civil law and mathematics under the charge of an uncle, canon of La Sainte Chapelle. In 1703 he came to Paris, where he continued the study of mathematics and physics. He soon made his presence felt in the highest circles, and in 1708, at the remarkably early age of twenty-four, was elected a member of the Académie des Sciences. From this time onwards for nearly half a century hardly a year passed in which the Mémoires de l'Académie did not contain at least one paper by Reaumur. At first his attention was occupied by mathematical studies, especially in geometry. In 1710 he was appointed to the charge of a great Government workthe official description of the useful arts and manufactureswhich led him to many practical researches that resulted in the establishment of manufactures new to France and the revival of neglected industries. For discoveries regarding iron and steel the regent Orleans awarded him a pension of 12,000 livres ; but, being content with his ample private income, he requested that the money should be secured to the Académie des Sciences for the furtherance of experiments on improved industrial processes. In 1731 he became greatly interested in meteorology, and invented the thermometer which bears his name. In 1735 family arrangements obliged him to accept the post of commander and intendant of the royal and military order of Saint Louis ; he discharged his duties in connexion with it with scrupulous attention, but declined to receive any of the emoluments. Whatever his other occupations were, he always found time for the systematic study of natural history, in which he took great delight. He was a born naturalist, gifted with rare powers of observation and de-scription,indeed his friends often called him the Pliny of the 18th century. He loved retirement and lived much at his country residences, at one of which, La Bermondière (Maine), he met with an accident, a fall from horseback, the effects of which proved fatal on 17th October 1757. He bequeathed his manuscripts, which filled 138 portfolios, and his natural history collections to the Académie des Sciences.
Reaumur was a man of wide attainments and great industry. His writings, sometimes on trivial topics, were frequently diffuse, yet always interesting. His mind was original and intensely practical. As a rule he avoided theoretical questions, but when he took them up his manner of treatment was remarkably clear, chiefly on account of an ingenious use of metaphor, often expanding into allegory. His memory was retentive, his information immense, and his kindliness of disposition such that his knowdedge and wealth seemed to be amassed only for the benefit of his friends. He always bore a high character, was a great favourite in society, and associated on terms of intimacy with the principal great men of the time in Europe.
Reaumur's scientific papers are too numerous to be recapitulated ; they deal with nearly all branches of science. His first paper, in 1708, was on a general problem in geometry, his last, in 1756, on the forms of birds' nests. He proved experimentally the fact, afterwards demonstrated theoretically by Du Hamel, that the strength of a rope is less than the sum of the strengths of its separate strands. He examined and reported on the auriferous rivers, the turquoise mines, the forests, and the fossil beds of France. He devised the method of tinning iron that is still employed, and investigated the differences between iron and steel, correctly showing that the amount of combustible matter (sulphur in the language of the old chemistry) is greatest in cast iron, less in steel, and least in wrought iron. His book on this subject (1722) was translated into English and German. The thermometer by which he is now best remembered was constructed on the principle of taking the freezing-point of water as 0°, and graduating the tube into degrees each of which was one-thousandth of the volume contained by the bulb and tube up to the zero mark. It was purely an accident dependent on the dilatability of the particular quality of alcohol employed which made the boiling-point of water 80° ; and mercurial thermometers the stems of which are graduated into eighty equal parts between the freezing and boiling points of water are not Reaumur thermometers in anything but name.
Reaumur wrote much on natural history. Early in life he described the locomotor system of the Echinodermata, and showed that the supposed vulgar error of Crustaceans replacing their lost limbs was an actual fact. In 1710 he wrote a paper on the possibility of spiders being used to produce silk, which was so celebrated at the time that the Chinese emperor Kang-he caused a translation of it to be made. He treated also of botanical and agricultural matters, and devised processes for preserving birds and eggs. He elaborated a system of artificial incubation, and made important observations on the digestion of carnivorous and graminivorous birds ; but his greatest work is the Mémoires pour servir à l'Histoire des Insectes, 6 vols., wdth 267 plates, Amsterdam, 1734-49. It describes the appearance, habits, and locality of all the known insects except the beetles, and is a marvel of patient and accurate observation. Amongst other important facts stated in this work are the experiments wdiich enabled Reaumur to prove the correctness of Peyssonel's hypothesis, that corals were animals and not plants, as was previously supposed.