In 1802 during a guest performance at the Königliches Hoftheater (royal court theatre) in Berlin he met Jakob Heinrich Laspeyres who encouraged him to publish parts of his entomological journals. Although he went to work immediately he planned the book at such a scale that it was not until 1805 that the first part, the natural history of the butterflies of Saxony, was published. Due to problems with the editor he was forced to discontinue the work and began an even more detailed treatment under the title "Die Schmetterlinge von Europa" (The Lepidoptera of Europe). In the same year he made a tour to Mannheim and Mainz and also to Frankfurt where he used all his spare time to work in the famous collection of Johann Christian Gerning. In December he was invited to Berlin and again exchanged views and experiences with Laspeyres.