John HerapathDied 24 Feb 1868 at age 77 (born 30 May 1790).English physicist and journalist was self-educated in mathematics and science. An early interest investigating a theory of lunar motion (1811) led to considering the nature of heat and derived an equation relating the pressure and volume of a gas to the number, mass and speed of its particles. He published a preliminary notice of his theory in Annals of Philosophy in 1816. In his later career, he took an interest in steam-powered transportation, and became the editor (1836) of Railway Magazine and Annals of Science. He published in it his own scientific papers, including one giving a calculation (1932) on the speed of sound in air, which is the first known calculation of the mean molecular speed of a molecule from the kinetic theory of gases, though it is often Joule's later work that is recognized for this accomplishment.