- A dictionary of medical eponyms

Mayer's law


First Law of Thermodynamics.

Related people

The law of conservation of energy.


The law of conservation of energy. Mayer was the first to formulate the law of equivalence between heat and work in physics. According to this law, energy can neither be created nor destroyed, it can only change its form.

This law is also associated with the British physicist James Prescott Joule (1818-1889) and the German physician  and physicist Hermann Ludwig Ferdinand von Helmholtz (1821-1894).

Mayer’s paper on this was printed in 1942, but it took a long time before the value og his work was reckognized. Now his discovery is counted among the greatest achievements in 19th century science.

Rudolf Julius Emanuel Clausius (1822-1888) codified the law in the words, "Die energie der Welt ist Konstant," where we take the word Welt to mean universe, not world. The law is later amended that matter and energy are also interchangeable in nuclear reactions.

"Es gibt nur eine einzige Kraft. Im ewigen Wechsel kreist dieselbe in der toten wie in der lebenden Natur. Dort wie hier kein Vorgang ohne Formveränderung der Kraft."
Julius Robert Meyer


Julius Robert Mayer:
Ueber die quantitative und qualitative Bestimmung der Kräfte. Written 1841, first published posthumously by J. J. Weyrauch in: Kleinere Schriften und Briefe, Stuttgart, 1893.

Julius Robert Mayer:
Bemerkungen über die Kräfte der unbelebten Natur.
[Liebig’s] Annalen der Chemie und Pharmacie, Heidelberg 1842.
In this publication Mayer formulates the general law of conservation of energy and calculates the mechanical equivalent of heat.

Julius Robert Mayer:
Bemerkungen über das mechanische Aequivalent der Wärme. Heilbronn, Verlag von Johann Ulrich Landherr,  1851. This was written primarily to maintain his priority.

James Prescott Joule:
On the calorific effects of magneto-electricity, and on the mechanical value of heat.
Philosophical Magazine, Series 3, 1843, 23: 263–276.
Read bu Joule at the meeting of the British Association at Cork, on August 21, 1843.

James Prescott Joule:
On the Changes of Temperature Produced by the Rarefaction and Condensation of Air.
Philosophical Magazine, Series 3 (Harper & brothers), 1845, 26: 369.
Joule wrote in his 1845 paper:
... the mechanical power exerted in turning a magneto-electric machine is converted into the heat evolved by the passage of the currents of induction through its coils; and, on the other hand, that the motive power of the electro-magnetic engine is obtained at the expense of the heat due to the chemical reactions of the battery by which it is worked.

James Prescott Joule:
On the mechanical equivalent of heat.
Philosophical Transactions of the Royal Society of London, 1850, 140: 61-82.   

Hermann von Helmholtz:
Ueber die Erhaltung der Kraft. Eine physikalische Abhandlung vorgetragen in der Sitzung der physikalischen Gesellschaft zu Berlin am 23. Juli 1847.
Berlin, 1847. Druck und verlag von G. Reimer.

Rudolf Julius Emmanuel Clausius (1822-1888):
Über die bewegende Kraft der Wärme und die Gesetze, welche sich daraus für die Wärmelehre selbst ableiten lassen. Annalen der Physik, Series 3, 1850, 79: 368–397, 500–524.
[On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom]
J. Tyndall:
Heat Considered as a Mode of Motion. New York: D. Appleton and Co., 1863.

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