John Herapath (30.05.1790-24.02.1868) was an English physicist. He was born in Bristol. He was self-taught. In 1815 he founded a private school of mathematics, which he ran until 1832, and in 1836 he became editor of the Railway Magazine and Annals of Science (later Herapath's Railway and Commercial Journal).
His main work was in the field of molecular physics and heat. He constructed a model of a gas according to which its particles are elastic spheres, constantly moving at high speed along straight segments and colliding with one another (the model of an ideal gas). Starting from these ideas, he explained the gas laws, diffusion, the propagation of sound in gases and the pressure of a gas, and calculated the speed of gas molecules. He derived the basic equation of the gaseous state, connecting the pressure and the volume of a gas with the mass and the speed of its particles, and gave (1832) a calculation of the speed of sound in air. He suggested the existence of an absolute zero of temperature (of “cold”). He was the author of a three-volume “Mathematical Physics”, in the third volume of which (1847) his kinetic theory is set out.