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. 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. The book provides a revealing tour of nineteenth-century debates concerning chemical theory.