During his stay in Berlin in 1764, Boswell lived in the house of Karl David Kircheisen, the president of the Berlin city council.
Johannes David HahnBorn Jul 09, 1729 in Heidelberg
Died Mar 09, 1784 in Leyden
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 Boswell in Holland 1763-64 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".