In the 1760s a group of amateur experimenters met and made friends in the English Midlands. Most came from humble families, all lived far from the center of things, but they were young and their optimism was boundless: together they would change the world. Among them were the ambitious toymaker Matthew Boulton and his partner James Watt, of steam-engine fame; the potter Josiah Wedgwood; the larger-than-life Erasmus Darwin, physician, poet, inventor, and theorist of evolution (a forerunner of his grandson Charles). Later came Joseph Priestley, discoverer of oxygen and fighting radical....