Julius Robert von Mayer (25 November 1814 – 20 March 1878) was a German physician, chemist, and physicist and one of the founders of thermodynamics.

[1][2] In 1842, Mayer described the vital chemical process now referred to as oxidation as the primary source of energy for any living creature.

His achievements were overlooked and priority for the discovery in 1842 of the mechanical equivalent of heat was attributed to James Joule in the following year.

Mayer was born on 25 November 1814 in Heilbronn, Württemberg (Baden-Württemberg, modern day Germany), the son of a pharmacist.

Mayer drew some additional interest in mathematics and engineering from his friend Carl Baur through private tutoring.

He also was the first person to describe the vital chemical process now referred to as oxidation as the primary source of energy for any living creature.

In 1848 he calculated that in the absence of a source of energy the Sun would cool down in only 5000 years, and he suggested that the impact of meteorites kept it hot.

His overlooked work was revived in 1862 by fellow physicist John Tyndall in a lecture at the London Royal Institution.

Mayer continued to pursue the idea steadfastly and argued with the Tübingen physics professor Johann Gottlieb Nörremberg, who rejected his hypothesis.

Mayer not only performed this demonstration, but determined also the quantitative factor of the transformation, calculating the mechanical equivalent of heat.

The result of his investigations was published 1842 in the May edition of Justus von Liebig's Annalen der Chemie und Pharmacie.

[4][5] It was translated as Remarks on the Forces of Inorganic Nature[6] In his booklet Die organische Bewegung im Zusammenhang mit dem Stoffwechsel (The Organic Movement in Connection with the Metabolism, 1845) he specified the numerical value of the mechanical equivalent of heat: at first as 365 kgf·m/kcal,[7] later as 425 kgf·m/kcal; the modern values are 4.184 kJ/kcal (426.6 kgf·m/kcal) for the thermochemical calorie and 4.1868 kJ/kcal (426.9 kgf·m/kcal) for the international steam table calorie.

However, in the meantime, his scientific fame had grown and he received a late appreciation of his achievement, although perhaps at a stage where he was no longer able to enjoy it.