Julius Robert von Mayer

Julius Robert von Mayer was born in Heilbronn in 1814 and trained as a physician. In 1840 he sailed as a ship's doctor on a Dutch merchant vessel to the East Indies, and it was there, bleeding feverish sailors off Java, that he made the observation that changed his life. The venous blood of the crew ran a brighter red in the tropics than he was used to in cool Germany: in the heat the body burned less fuel to keep warm, drew less oxygen from the blood, and returned it less depleted.

From this clinical accident Mayer reasoned his way, alone and without a laboratory, to a universal principle: that heat and mechanical work are interconvertible forms of one conserved quantity. In an 1842 paper he stated the conservation of energy and even produced an estimate of the mechanical equivalent of heat from the difference between the two heat capacities of a gas — a year before Joule's celebrated paddle-wheel measurements.

As an outsider to the scientific establishment, with a physician's training rather than a physicist's, Mayer was largely ignored. Priority disputes with Joule, the deaths of several of his children, and a lack of recognition drove him to a breakdown; in 1850 he attempted suicide and was for a time confined to asylums. His work was nearly forgotten.

Vindication came late. In the 1860s Clausius, Helmholtz, and especially John Tyndall championed his priority, and Mayer was at last honoured — awarded the Copley Medal of the Royal Society in 1871 and ennobled as 'von' Mayer. He is now remembered as one of the independent discoverers of the first law of thermodynamics, the one who reached it by pure reasoning from physiology.