Julius Robert Mayer (25.02.1814-20.03.1878) was a German physician. He was one of the first to discover a fundamental law of nature, the law of the conservation and transformation of energy. He was born in Heilbronn. He graduated from the University of Tübingen (1838), taking the degree of Doctor of Medicine. In 1839 he worked in clinics in Paris. In 1840—41, as a ship's doctor, he took part in a voyage to the island of Java. During the voyage he noticed that the colour of the sailors' venous blood in the tropics was considerably lighter than in northern latitudes. This change in the colour of venous blood led him to the idea that there is a connection between the consumption of substance and the generation of heat. He also established that the quantity of products oxidised in the human body increases as the work it performs increases. All this gave Mayer grounds in 1840 for supposing that heat and mechanical work are capable of being transformed into each other. He set out the results of his research in the works “On the Quantitative and Qualitative Determination of Forces” (1841, published in 1881) and “Remarks on the Forces of Inanimate Nature” (1841, published in 1842). In these works Mayer was the first to formulate the law of the conservation of energy, and in more detail in the work “The Organic Motion in its Connection with Metabolism” (1845); he also calculated theoretically the mechanical equivalent of heat.
Mayer's outstanding discovery, however, was not recognised, and his work (1845), which he published at his own expense as a separate pamphlet, long remained almost unknown. J. Joule, and then H. Helmholtz, came to be named as the discoverer of the law. Mayer's attempts to defend his priority in the discovery of the law of the conservation and transformation of energy brought upon him attacks and persecution from local scientists. This told on his mental state and led to a severe nervous disorder, and it made active scientific work impossible. Only in the 1850s and 1860s was Mayer's priority in the discovery of the law of the conservation of energy recognised.
Mayer was also the first to express the idea that the radiation of the Sun leads to a decrease in its mass.