Closing the Loop: Ewald von Kleist and the Origins of the Leyden Jar

This essay examines Ewald von Kleist’s 1745 invention of the Leyden jar using previously overlooked letters and features of his experimental apparatus to address lingering mysteries concerning the discovery. It has traditionally been claimed that Kleist unknowingly violated standard practice by grounding the device, the assumption being that this was the only way to obtain his remarkable results. In recent years, however, this interpretation has faced serious challenges, with experimental replications showing substantial shocks without grounding and period sources providing reason to think that Kleist was insulated during the process. Supposing that Kleist was insulated raises puzzles of its own, however, as his results appear more extreme than such a charging method suggests. The missing piece, the author argues, is found in the unique nature of his setup. Drawing on established and novel sources, the essay shows how Kleist’s operation of his generator resulted in a closed circuit, explaining the strong charges cited by proponents of the traditional mistake narrative while upholding the absence of grounding.