J. Willard Gibbs

Josiah Willard Gibbs was born in 1839 in New Haven, Connecticut, the son of a Yale professor of sacred literature. He earned one of the first PhDs in engineering granted in the United States from Yale in 1863, then spent three years studying in Paris, Berlin and Heidelberg, absorbing the latest European mathematics and physics. He returned to Yale and in 1871 was appointed professor of mathematical physics — a position he held, at first without salary, for the rest of his life.

Between 1875 and 1878 Gibbs published On the Equilibrium of Heterogeneous Substances, a long and densely mathematical memoir that single-handedly founded chemical thermodynamics. In it he introduced the chemical potential, the Gibbs free energy, and the phase rule, and showed how to predict the equilibrium of multi-component, multi-phase systems. Published in the obscure Transactions of the Connecticut Academy, the work was at first read by almost no one, though Maxwell in England recognised its importance and built a plaster model of Gibbs's thermodynamic surface.

In 1902 Gibbs published Elementary Principles in Statistical Mechanics, the book that gave the field its name. Abstracting away from the molecular models of Boltzmann and Maxwell, he organised the subject around statistical ensembles and the partition function, providing the framework — microcanonical, canonical and grand canonical ensembles — in which all of equilibrium statistical mechanics is still taught.

Gibbs was famously modest and retiring, never marrying and rarely leaving New Haven. He also developed modern vector analysis for his teaching. He died in 1903, the year after his statistical-mechanics book appeared, not living to see quantum mechanics make his abstract sum over discrete states not merely convenient but unavoidable.