Our story must now follow a more zigzag chronology. (Those more comfortable with linear timelines may want to consult the chronology at the end of the book.) Part 2 followed the development of thermodynamics from Carnot in the 1820s to Nernst in the 1930s. The history now returns to the 1820s and 1830s, with the same scientific scenery that inspired the thermodynamicists, the topic of the day being the mysterious and intriguing matter of conversion processes. It was plain to the scientists of the early nineteenth century that the many interconvertible effects—thermal, mechanical, chemical, electrical, and magnetic—demanded unifying principles. Thermodynamicists concentrated at first on thermal and mechanical effects, and from them refined the concepts of energy and entropy and three great physical laws. Eventually, by the end of the nineteenth century, thermodynamicists had discovered that the language of their science encompassed all macroscopic effects— indeed, the entire universe.
There were other unities to be discovered at the same time. In 1820, Oersted observed that a wire carrying an electric current slightly disturbed the magnetic needle of a nearby compass: an electric effect produced a magnetic effect. Oersted's colleagues were not impressed, but an ambitious young laboratory assistant at the Royal Institute in London was; his name was Michael Faraday. In a string of brilliantly designed experiments, Faraday discovered many more “electromagnetic” effects, including those that make possible modern electric motors and generators. In one of the last and most difficult of these experiments, Faraday made the stunning discovery that polarized light is affected by a magnetic field. With that observation he brought light into the domain of electromagnetic phenomena.
Faraday was guided by his superb skill in the laboratory—he was the greatest experimentalist of the nineteenth century—and also by a revolutionary theory. He believed that magnetic, electric, and electromagnetic effects were transmitted through space along “lines of force,” which collectively defined a “field.” Once it was generated, the field could exist anywhere, even in otherwise empty