This study is an outgrowth of our interest in the history of modern chemistry. The paucity of reliable, quantitative knowledge about past science was brought home forcibly to us when we undertook a research seminar in the comparative history of modern chemistry in Britain, Germany, and the United States. That seminar, which took place at the University of Pennsylvania in the spring of 1975, was paralleled by one devoted to the work of the "Annales School." The two seminars together catalyzed the attempt to construct historical measures of change in aspects of one science, or "chem ical...