Julius Robert Mayer


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(1814–1878) German physician and physicist

Mayer, the son of an apothecary from Heilbronn in Germany, studied medicine at the University of Tübingen, where he seems to have been a mediocre student. He continued his studies abroad in Vienna and Paris before taking up an appointment in 1840 as a ship's physician on a vessel bound for Java. On his return in 1841 he settled in Heilbronn working as a general practitioner.

When Mayer sailed to Java he was familiar with the views of Antoine Lavoisier that animal heat is produced by slow combustion in the body. Being forced to bleed some of the crew at Surabaya, he found that venous blood was surprisingly bright. Indeed, at first he thought that he had cut an artery by mistake. “This phenomenon riveted my earnest attention,” he reported, drawing the correct conclusion that the blood was redder because in the tropics the body does not need to burn as much oxygen to maintain body temperature as it does in temperate regions. The observation led Mayer to speculate about the conversion of food to heat in the body, and also the fact that the body can do work. He came to the view that heat and work are interchangeable – that the same amount of food can be converted to different proportions of heat and work, but the total must be the same.

Moreover, Mayer appreciated that this equivalence should hold universally and tried to apply it to other systems and to make it quantitative. Unfortunately, at the time he was confused about such concepts as force and work and his ideas were presented in an obscure metaphysical style. His first paper on the subject was sent to Annalen der Physik (Annals of Physics); the editor, Johann Poggendorf, did not even acknowledge Mayer's letter. The paper was published in 1842 by Justus von Liebig in the journal Annalen der Chemie und Pharmazie (Annals of Chemistry and Pharmacy). The paper was almost totally ignored and Mayer published, in 1845, a pamphlet at his own expense – Organic Motion Related to Digestion – which fared no better than his paper.

In his arguments Mayer used the specific heat capacities of gases, i.e., the heat required to produce unit temperature rise in unit mass of gas. It was known that the specific heat capacity of a gas maintained at constant volume is slightly smaller than that at constant pressure. This difference in heat, for a given quantity of gas, Mayer interpreted as the work done by a gas expanding at constant pressure. He was able to find the amount of work required to produce unit amount of heat – thus obtaining what was later known as the mechanical equivalent of heat (J). He found a weight of 1 gram falling 365 meters corresponds to heating 1 gram of water 1°C. (This is equivalent to a value of J of 3.56 joules per calorie; the modern conversion factor is 4.18 joules per calorie.)

Mayer clearly anticipated James Joule and Hermann von Helmholtz in the discovery of the law of conservation of energy. The lack of recognition seems to have affected him strongly, for in the early 1850s he attempted suicide. His work was eventually recognized and he received many honors, including the Rumford medal of the Royal Society (1871).


Subjects: Science and Mathematics.

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