In the early nineteenth century many scientists had glimmerings of the conservation-of-energy principle. The three most important among these were the Frenchman Marc Séguin, the American-born, well-travelled soldier of fortune Benjamin Thompson, and the chief engineer of the city of Copenhagen, Ludwig Colding.

The three men whose work later in the nineteenth century was crucial in bringing clarity to this principle were two Germans, the physician Julius Robert Mayer and the great polymath Hermann von Helmholtz, and the British amateur scientist James Joule. In a lecture delivered by Helmholtz on February 7, 1854, in Königsberg on "The Interaction of Natural Forces,"

he referred to Mayer as "the founder" in 1842 of the principle of conservation of energy and acknowledged Mayer's priority in this discovery over Colding (1843), Joule (1843), and Helmholtz himself (1847). Rudolf Clausius agreed with Helmholtz and put...