Jacques-Barthélemy Micheli du Crest

Jacques-Barthélemy Micheli du Crest (Geneva, 28 September 1690 – Zofingen, 29 March 1766) was a military engineer, physicist and cartographer from the Republic of Geneva, now in Switzerland. Born into the aristocracy, he eventually fled to France as an enemy of Geneva and spent his later years in Aarburg Castle as a political prisoner. During his time there, he mapped the Alps accurately using rudimentary tools. One of his other major accomplishments whilst in exile was to create a thermometer and a temperature scale, which was commonly used in Switzerland and around Europe until it became obsolete in the 19th century.

Early life and career Du Crest was born in Geneva to Jacques Micheli du Crest, a captain in the mercenary troops of France, and Elisabeth Calandrini. He graduated from the Collège de Genève in 1705. and was an outspoken critic of the planned wall around Geneva. Eventually, due to his views and publishing pamphlets such as "Maxims of a Republican", he was declared an enemy of Geneva, his rights as a citizen were revoked, and his lands were confiscated. Du Crest fled to Paris in 1731.

Scientific achievements Du Crest devoted a significant portion of his life in exile to scientific study, making pioneering developments in cartography and the measurement of temperature.

Temperature scale Du Crest believed that the temperature of the Earth was fundamentally fixed, based on the supposition that cellars and mines maintained an equal temperature. He used this "temperature of the terrestrial globe" as one fixed point, measured in a cellar below Paris Observatory, and the temperature of boiling water as a second fixed point. His scale between these points was then divided into one hundred equal degrees.

Thermometer Du Crest rejected mercury thermometers, stating that the substance was too difficult to purify, preferring instead alcohol which had passed the gunpowder test. He created a thermometer based the expansion of alcohol, calibrated using mercury.

Mapping the Alps

During his time at Aarburg Castle he published many meteorological papers