Hermann Kopp (1817-1892) is best remembered today as a historian of chemistry, but during his lifetime he was one of the most eminent chemists of his day, and one of the earliest pioneers of physical chemistry. Late in his career he wrote an endearing fantasy about personified molecules. Published in 1882, Aus der Molecular-Welt (From the Molecular World) portrayed the intimate details of what might actually be happening in the sub-microscopic world; the atoms and molecules we meet there have agency, personalities, sometimes even dialog. Filled with appealing tropes, humor, and whimsical asides, Kopp's short book provided an examination of the chemistry and physics of his day that was always light-hearted on the surface, but often surprisingly profound. Properly interpreted, the book provides a revealing tour of nineteenth-century debates concerning chemical theory. It is here translated into English, richly annotated, and equipped with an illuminating preface by a leading historian of chemistry. It provides entertaining reading to practicing chemists, as well as new insights to historians of science.

Educated first as a chemist, Alan J. Rocke earned a Ph.D. in history of science at the University of Wisconsin-Madison in 1975. Today he is the Henry Eldridge Bourne Professor of History at Case Western Reserve University in Cleveland, Ohio, where he has been teaching since 1978. Rocke is the author of five books and nearly fifty journal articles on the history of chemistry, especially the theoretical development of the science in Europe during the course of the nineteenth century. He is a Fellow of the American Association for the Advancement of Science, and in 2000 received the Dexter Award from the American Chemical Society for lifetime achievement in the history of chemistry.