Julius Robert Mayer and the principle of energy conservation

Julius Robert von Mayer was among the first to state the principle of energy conservation. As a medical doctor, he was interested in the relationship between heat and work, being stimulated by observations and considerations regarding the physiology of the human body. In 1842, he published a first manuscript in which he reported the value of the mechanical equivalent of heat; then, in a paper in 1845, he elucidated the procedure followed for the calculation of the equivalent. The result achieved by Mayer, based only on theoretical calculations, was presented before the experimentally determined value obtained by Joule in 1847 and remains of capital interest in the history of thermodynamics.