Temperature > 18 - René-Antoine Ferchault de Réaumur

René-Antoine Ferchault de Réaumur (La Rochelle, 28 February 1683 - Saint-Julien-du-Terroux, 17 October 1757) was a French scientist, biologist, naturalist and physicist.

René-Antoine Ferchault de Réaumur was born on 28 February 1683 in La Rochelle, and was educated in Paris. He studied philosophy at the Jesuit College. In 1699 he went to Bourges to study civil law and mathematics under the tutelage of an uncle, a canon of Saint-Chapelle. In November 1738 he was elected a member of the Royal Society. He worked on subjects as varied as metallurgy, temperature, porcelain and particularly entomology. In 1731, he invented the temperature scale that bears his name, the Réaumur scale, whose fixed points are the freezing point of water (0°R) and its boiling point (80°R). Thus, the unit of this scale, the Réaumur degree, is worth 4/5 of 1 degree Celsius and has the same zero as the degree Celsius.

The thermometer contains diluted alcohol and was built on the principle of taking the freezing point of water as zero. The graduation of the tube was made in degrees in which each of them was one thousandth of the volume contained in the bulb. Réaumur chose alcohol instead of mercury, claiming that it expanded more visibly, but this choice caused problems, since his original thermometers were very bulky, and the low boiling point of alcohol made them unsuitable for many applications.