In the 1850s the Glasgow professor of natural philosophy (physics), William Thomson, and his colleague in engineering science, Macquorn Rankine, revolutionized the traditional language of mechanics with new terms such as "actual" ("kinetic" from 1862) and "potential" energy. Rankine also constructed a new "science of thermodynamics" by which engineers could evaluate the imperfections of heat engines. By the end of the decade, Thomson and Rankine had been joined by like-minded scientific reformers, most notably the Scottish natural philosophers James Clerk Maxwell, Peter Guthrie Tait, and Balfour Stewart, and the telegraph engineer Fleeming Jenkin. As a group, these physicists and engineers created a new "science of energy" intended to account for everything from the smallest particle to the largest heavenly body.

The fourth child of James and Margaret Thomson, William was born in 1824 in Belfast, then Ireland's leading industrial center, where his...