In 1767 Raspe was again advanced by being appointed Professor at the Collegium Carolinum in Cassel, and keeper of the landgrave of Hesse's rich and curious collection of antique gems and medals. He was shortly afterwards appointed Librarian in the same city, and in 1771 he married. He continued writing on natural history, mineralogy, and archaeology, and in 1769 a paper in the 59th volume of the Philosophical Transactions, on the bones and teeth of elephants and other animals found in North America and various boreal regions of the world, procured his election as an honorary member of the Royal Society of London. His conclusion in this paper that large elephants or mammoths must have previously existed in boreal regions has, of course, been abundantly justified by later investigations. When it is added that Raspe during this part of his life also wrote papers on lithography and upon musical instruments, and translated Algarotti's Treatise on "Architecture, Painting, and Opera Music," enough will have been said to make manifest his very remarkable and somewhat prolix versatility. In 1773 he made a tour in Westphalia in quest of MSS., and on his return, by way of completing his education, he turned journalist, and commenced a periodical called the _Cassel Spectator_, with Mauvillon as his co-editor. In 1775 he was travelling in Italy on a commission to collect articles of vertu for the landgrave, and it was apparently soon after his return that he began appropriating to his own use valuable coins abstracted from the cabinets entrusted to his care. He had no difficulty in finding a market for the antiques which he wished to dispose of, and which, it has been charitably suggested, he had every intention of replacing whenever opportunity should serve. His consequent procedure was, it is true, scarcely that of a hardened criminal. Having obtained the permission of the landgrave to visit Berlin, he sent the keys of his cabinet back to the authorities at Cassel--and disappeared. His thefts, to the amount of two thousand rixdollars, were promptly discovered, and advertisements were issued for the arrest of the Councillor Raspe, described without suspicion of flattery as a long-faced man, with small eyes, crooked nose, red hair under a stumpy periwig, and a jerky gait. The necessities that prompted him to commit a felony are possibly indicated by the addition that he usually appeared in a scarlet dress embroidered with gold, but sometimes in black, blue, or grey clothes. He was seized when he had got no farther than Klausthal, in the Hartz mountains, but he lost no time in escaping from the clutches of the police, and made his way to England. He never again set foot on the continent.