This essay examines the physicist Ernst Mach’s popular work. Like many other scientists in late nineteenth-century Central Europe, he viewed the popular genre as a means not only of edifying the lay public but of communicating arguments to other specialists. In many cases, he used his popularizations to draw his colleagues’ attention to the biological and evolutionary features of scientific reasoning, although his own understanding of those features changed in the 1880s and early 1890s. Notably, he came to believe that (...) human beings instinctively read substances into nature. Several years after adopting this new perspective on substance, he incorporated it into a series of popular works that were intended to outline his views on thermodynamics in general and to weigh in on the controversy over “energetics” that erupted at the 1895 Versammlung Deutscher Naturforscher und Ärtze. (shrink)