Julius von Mayer (1814–1878) was a German physicist and one of the key figures in the development of the concept of energy conservation in physics. He is best known for formulating the first law of thermodynamics, which states that energy cannot be created or destroyed, only transformed from one form to another. Mayer's work laid the foundation for the understanding of the relationship between different forms of energy, such as heat and mechanical work.
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Julius von Mayer argued for a quantitative equivalence between mechanical work and heat. His 1842 paper connects compression of a gas with its heat capacity. In a modern ideal gas example, heating at constant pressure includes expansion work that is absent at constant volume. Because an ideal gas's internal energy depends only on temperature, its molar heat capacities satisfy , where is the molar gas constant. The heat capacity difference thus supplies a route to comparing thermal and mechanical units of energy.[ref]
Remarks on the Forces of Inorganic Nature by Julius Robert Mayer. Final compression and heat-capacity argument; ideal-gas explanation expressed here in modern notation
Physician and natural philosopher who contributed to the conservation-of-energy programme in the 1840s, including an argument for the mechanical equivalent of heat.
Portrait of Julius von Mayer
. Wellcome Library, London / Wellcome Collection. CC BY 4.0, via Wikimedia Commons. Source.