The German Genius

place: by the 1840s it was the most important German journal of physics, though many new journals proliferated in that decade, just as many new medical instruments began to be introduced. Johann Christian Poggendorff, the editor of the Annalen since 1824, could make or break scientific careers. 10 Poggendorff edited the Annalen until he died in 1877, when its pre-eminence was so assured that the Berlin Physical Society took it over, with Gustav Wiedemann as editor, and Hermann von Helmholtz as adviser on theoretical matters. In physics, a clear division of labor was already emerging between the experimenter and the theoretician. By the 1860s or 1870s, research in physics, including theoretical physics, was regarded as an end in itself, not just as an adjunct to teaching: beginning in the 1870s, professorships of theoretical physics were established at a number of German universities. Mary Jo Nye has tracked these institutions, in particular the Physikalisch-Technische Reichsanstalt (PTR) at Berlin-Charlottenburg and calculates that 800 physicists and chemists from Britain and North America earned doctorates in Germany in the nineteenth century and that thirty-nine important British scientists came under German influence. 11 By the same token, new laboratories were being built all over Europe, differing from their predecessors in kind as well as number, no longer merely teaching aids but spaces for research in their own right. “Experiment increasingly looked like the key to unlocking nature’s secrets.” 12
    It was in the laboratory that more and more experimenters were looking for ways to turn one kind of force into another. To Romantic natural philosophers in particular, as Kuhn has said, these “proliferating instances” of the apparent conversion of one kind of force into another seemed to confirm the underlying unity of nature—they were mutually convertible because they were different manifestations of the same underlying power. At the same time, pragmatists saw economic possibilities in these transformations. The new technology of photography used light to produce chemical reactions. The voltaic pile seemed to turn chemical forces into electricity, a major concern in industrializing and urbanizing societies. Above all, there was the steam engine, a machine for producing mechanical force from heat. 13
    T HE D ISCOVERY /I NVENTION OF E NERGY
     
    In the eighteenth century, heat and electricity had been explained by supposing there were “imponderable fluids and ethers” which interacted with the atoms of ordinary matter. In 1812 the Academy in Paris announced it would offer its Grand Prix des Mathématiques to whoever could show how heat moved through matter. 14 Joseph Fourier’s mathematical theory of heat, published in 1822, brought heat and mathematics together, while James Prescott Joule’s experiments in 1843 established the equivalence of heat and mechanical work. Two years later, Julius Mayer published his observations about body heat and blood color.
    With hindsight, everything can be seen as pointing toward the theory of the conservation of energy, but it still required someone to formulate these ideas clearly; that occurred in the seminal memoir of 1847 by Hermann von Helmholtz (1821–94). In On the Conservation of Force , he provided the requisite mathematical formulation, linking heat, light, electricity, and magnetism by treating these phenomena as different manifestations of “energy.” 15
    The son of a Prussian Gymnasium teacher, Helmholtz studied medicine at the University of Berlin, funded by a Prussian army scholarship. In return, he served as a medical officer before becoming associate professor of physiology at the University of Königsberg in 1849. 16 Helmholtz’s 1847 essay was privately published as a pamphlet. Like Mayer, he had sent his paper to Poggendorff at the Annalen der Physik but was rebuffed. Helmholtz’s previous physiological publications had all been designed to show how the heat of animal bodies and their mucular activity could be traced to the oxidation of food—that the human engine was little different from the steam engine. He did not think there were forces entirely peculiar to living things but instead that organic life was the result of forces that were “modifications” of those operating in the inorganic realm. 17 In the purely mechanical universe envisaged by Helmholtz there was an obvious connection between human and machine work. 18
    While Mayer