He is stated also to have rendered some assistance to a young nobleman in sowing his wild oats, a sequel to his university course which may possibly help to explain his subsequent aberrations. The connection cannot have lasted long, as in 1762, having already obtained reputation as a student of natural history and antiquities, he obtained a post as one of the clerks in the University Library at Hanover.

No later than the following year contributions written in elegant Latin are to be found attached to his name in the Leipsic Nova Acta Eruditorum. In 1764 he alluded gracefully to the connection between Hanover and England in a piece upon the birthday of Queen Charlotte, and having been promoted secretary of the University Library at Göttingen, the young savant commenced a translation of Leibniz's philosophical works which was issued in Latin and French after the original MSS. in the Royal Library at Hanover, with a preface by Raspe's old college friend Kästner (Göttingen, 1765). At once a courtier, an antiquary, and a philosopher, Raspe next sought to display his vocation for polite letters, by publishing an ambitious allegorical poem of the age of chivalry, entitled "Hermin and Gunilde," which was not only exceedingly well reviewed, but received the honour of a parody entitled "Harlequin and Columbine." He also wrote translations of several of the poems of Ossian, and a disquisition upon their genuineness; and then with better inspiration he wrote a considerable treatise on "Percy's Reliques of Ancient Poetry," with metrical translations, being thus the first to call the attention of Germany to these admirable poems, which were afterwards so successfully ransacked by Bürger, Herder, and other early German romanticists.

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 archæology, 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.

He was already an excellent English scholar, so that when he reached London it was not unnatural that he should look to authorship for support. Without loss of time, he published in London in 1776 a volume on some German Volcanoes and their productions; in 1777 he translated the then highly esteemed mineralogical travels of Ferber in Italy and Hungary. In 1780 we have an interesting account of him from Horace Walpole, who wrote to his friend, the Rev. William Mason: "There is a Dutch sçavant come over who is author of several pieces so learned that I do not even know their titles: but he has made a discovery in my way which you may be sure I believe, for it proves what I expected and hinted in my 'Anecdotes of Painting,' that the use of oil colours was known long before Van Eyck." Raspe, he went on to say, had discovered a MS. of Theophilus, a German monk in the fourth century, who gave receipts for preparing the colours, and had thereby convicted Vasari of error. "Raspe is poor, and I shall try and get subscriptions to enable him to print his work, which is sensible, clear, and unpretending." Three months later it was, "Poor Raspe is arrested by his tailor. I have sent him a little money, and he hopes to recover his liberty, but I question whether he will be able to struggle on here." His "Essay on the Origin of Oil Painting" was actually published through Walpole's good service in April 1781. He seems to have had plans of going to America and of excavating antiquities in Egypt, where he might have done good service, but the bad name that he had earned dogged him to London. The Royal Society struck him off its rolls, and in revenge he is said to have threatened to publish a travesty of their transactions. He was doubtless often hard put to it for a living, but the variety of his attainments served him in good stead. He possessed or gained some reputation as a mining expert, and making his way down into Cornwall, he seems for some years subsequent to 1782 to have been assay-master and storekeeper of some mines at Dolcoath. While still at Dolcoath, it is very probable that he put together the little pamphlet which appeared in London at the close of 1785, with the title "Baron Munchausen's Narrative of his Marvellous Travels and Campaigns in Russia," and having given his jeu d'esprit to the world, and possibly earned a few guineas by it, it is not likely that he gave much further thought to the matter. In the course of 1785 or 1786, he entered upon a task of much greater magnitude and immediate importance, namely, a descriptive catalogue of the Collection of Pastes and Impressions from Ancient and Modern Gems, formed by James Tassie, the eminent connoisseur.