Professor of Philosophy and Natural Sciences at the University of Utrecht (1753-1775), and Director of the Botanical Garden at the same place (1759-1775). Professor of medicine and chemistry at the University of Leyden (1775-?). According to a note in Boswell in Holland he was the sometime physician to Belle de Zuylen.
Life with Boswell
Boswell heard Hahn lecture about Nitre (a chemical used for the making of gunpowder) at Utrecht on January 19, 1764. On April 8 Boswell supped at the professor's with whom he also met on May 21. On this last occasion, Hahn "told stories of Rücker's forgetting law, and officer hearing voices blaspheming".