Steno’s Disciple: Jacobæus, Leibniz, and the Lost Geological Manuscripts
Nicolas Steno (1638–1686) was among the most influential anatomists and natural philosophers of the seventeenth century. As Nuno Castel-Branco shows in his splendid new book on Steno, The Traveling Anatomist. Nicolaus Steno and the Intersection of Disciplines in Early Modern Science (University of Chicago Press, 2025), Steno made an important impact in all the places that mattered in mid-seventeenth-century Europe, in Leiden, in Paris, in Florence, even in London although he never went there.[1][2] And then of course also in his native Copenhagen, even if the few years he taught there from 1672 to 1674—not being appointed to a real professorship because his earlier conversion to Catholicism disallowed it in Lutheran Denmark—left him frustrated, underappreciated, and insufficiently paid. However, as an itinerant scholar with an erratic biography, he never gathered followers around him and had no disciples. Except for one: the Danish physician and naturalist Holger Jakobsen, or Oligerus Jacobæus (1650–1701).
Originally from Aarhus, Jacobæus was a young naturalist and physician, part of the Bartholin academic dynasty. He was the son of Thomas Bartholin’s sister, Anne, and, from 1681, also his son-in-law when he married Thomas’s daughter and his own cousin, Anne Margrethe. Jacobæus was trained by Thomas Bartholin and Steno’s old European travel companion, Ole Borch, at the University of Copenhagen. In 1671 he travelled to Holland with Johan Worm, son of the famous early archaeologist Ole Worm, and attended lectures by Frans de la Boë Sylvius and dissections by Drelincourt, but their trip was interrupted by the French invasion of Holland after only 10 months. His return to Denmark in 1672 coincided with Steno’s appointment as regius anatomicus in Copenhagen, and over the following two years he studied under, and became very close to, Steno.
In 1675, Jacobæus undertook a second, longer perigrinatio academica in the company of his two cousins, Caspar and Christoffer Bartholin. During this trip, Jacobæus kept a journal mostly recording local customs and food, but also various academic encounters.[3] They spent a year in Paris, from early April 1675 to late March 1676, spent time at the court of Count Cosimo III with Steno, and arrived in Rome in October 1676. Later, in March-April 1677 they travelled to Pisa and Liverno where they met again with Steno. They returned to Copenhagen in August 1677. The year after, Jacobæus undertook yet a third trip, this time to Holland where he met Steno’s former host in Amsterdam, Gerard Blasius, and to London and Oxford where he met Robert Boyle and attended sessions at the Royal Society, among other things.[4]
While his fellow Danes were traveling Italy in 1676–1677, Steno helped them organise their trip, but meanwhile also did his best to convert them and almost succeeded with Jacobæus until Caspar Bartholin took the initiative to bring them all out of Steno’s reach, so they could return to Denmark with their Lutheran faith intact.[5] They essentially without saying goodbye. Nonetheless, at some point in time, Jacobæus was charged by Steno with securing his scientific legacy. Jacobæus was to do this by doing academic work of his own, defending and deepening that of Steno’s, which indeed Jacobæus later did in numerous lectures and publications. But he was also to do it by publishing Steno’s unpublished natural scientific writings. And this he did not, which is very unfortunate, because a treasure trove of unpublished work existed. Among Steno’s most famous works we find the 1669 De solido intra solidum naturaliter contento dissertationis prodromus which contains the main results of the geological investigations he undertook in Italy. As indicated by the title (prodromus), it was however only meant as a preliminary treatise written in preparation to a more complete geological account to be included in a prospective edition of all Steno’s natural philosophical work.[6] But the reorientation of his career towards the priesthood and ecclesiastical commitments after 1675 led him to abandon that project, leaving us to wonder about what happened to all the research made in view of this more developed geological work.
The only Steno researcher to have explored in any detail the whereabouts of Steno’s unpublished geological manuscripts is Axel Garboe, a Danish Lutheran priest and geologist who in 1948 published a short dissertation in Danish on the destiny of Steno’s geological work, followed up in 1960 with a short supplementary article in English.[7] Garboe’s work remains the main source of all subsequent discussion of the matter.[8] The information that Jacobæus was charged with editing Steno’s work does however already figure in Vilhelm Maar’s introduction to his 1910 edition of Jacobæus’s travel diary.[9] The assumption is based on the following text, found in Joachim Friedrich Feller’s 1718 edition of texts by Gottfried Wilhelm Leibniz, the Otium Hanoveranum:
Mr. Otto Sperling, historiographer of Denmark, had the intention [avoit dessein] to write the life of Cranz, and I provided him with some notes for that. If this life is completed, it ought to be published. / I have learned that the late Mr. Steno, no longer undertaking profane writing, charged Mr. Oliverius [sic] Jacobæus, Danish physician, to develop and pursue his thoughts on natural geography and the physical changes of the Earth’s surface. I would like to know if that scholar actually works on it.[10]
The status of the text is unclear. Feller does not date it, says nothing of its provenance, and publishes it under a title not, I think, Leibniz’s own: Memoire donné à un Voyageur du Nord. Garboe, for his part, describes the passage as part of a letter to the Danish historian and jurist, Otto Sperling (1634–1715), with whom Leibniz entertained a scattered correspondence in 1700–1706.[11] This is manifestly false: Leibniz would hardly send a text to Sperling that speaks of Sperling himself in the third person! Moreover, Leibniz’s use of the past tense (avoit dessein) could suggest that the text was written after Sperling’s death, so no earlier than 1715. That is almost three decades after Steno died in 1686. This configuration of circumstances creates some uncertainty about the status and credibility of the account and, consequently, also about the role it assigns to Jacobæus in relation to Steno.
When perusing the more recent volumes of the ongoing edition of Leibniz’s Mathematische, naturwissenschaftlicher, und technischer Briefwechsel, we do however hit upon a text that affords us some additional information on the matter. Mid-August 1683, Leibniz wrote a young German living in Copenhagen, Christian Albrecht Walter (1655–1687), asking him for information:
Since I know you have always been curious and that I am of the same temperament, I take the liberty to ask for some news about Copenhagen curiosities. Mr. Steno told me at some other time that he had given his manuscript about natural knowledge to some friends able to pursue them, after he had renounced on this kind of studies and, if I am not mistaken, he had given the geographical [papers] (concerning the constitution and physical changes of the terrestrial globe, about which he had important meditations) to Mr. Holger Jacobæus, and the anatomical [papers] to Mr. Caspar Bartholin. Please, Sir, would you be so kind as to inquire about them, in particular those regarding the terrestrial globe, for he attempts, I believe, to prove by physical reasons that a universal deluge took place and numerous beautiful things in conformity with Holy Scripture.[12]
Walter did not reply as far as we know. The letter does not make an enormous difference. It does not help us understand what happened to the manuscripts, let alone locate them or reassure us that they still could exist. But the letter does strengthen the original hypothesis about Jacobæus’s assigned role by clarifying the source of Leibniz’s information, namely Steno himself in personal conversation. This moreover allows us to specify when Leibniz obtained that information, namely while Steno was apostolic envoy at the Court of Hanover. He arrived in November 1677 and left for Münster in October 1680. The conversation with Leibniz must have taken place within that time span. The letter finally suggests that Steno must have given his instructions to Jacobæus while still in Italy, likely around March-April 1677 right before Jacobæus and his travel companions left, and not long before Steno was back in Rome in May to prepare for his departure for Hanover, where he arrived in November 1677.
What happened to the manuscripts then? The scarce information we have is not encouraging for researchers. In 1960, Garboe published a supplement to his original 1948 dissertation, including some new information he had found while exploring manuscripts at the National Library in Florence, in particular a passage in a letter from 9 July 1680 from Jacobæus to Antonio Magliabecchi, Cosimo III’s eccentric librarian:
I am sorry that the books and other precious things which I left in Florence or Livorno if my memory does not fail me, have never reached me here […] Nicolaus Steno’s servant who does not take much care of our things, has caused this.[13]
As Garboe already noted, the letter makes it clear, first, that anyone determined to search further for Steno’s lost manuscripts would be wise to search for them in Italy rather than in Denmark. Second, it suggests that Jacobæus should be exonerated from any suspicion that he was negligent in carrying out his teacher’s wish to edit his work. He most likely never received the manuscripts, perhaps due to a negligent manservant in Italy.
MOGENS LÆRKE
[1] For another recent, indispensable resource on Steno, see T. Kardel and P. Maquet, in Nicolaus Steno. Biography and Original Papers of a 17th-Century Scientist, 2nd ed. (Dordrecht: Springer, 2018).
[2] Specifically on Steno in Paris, see G. Scherz, “Da Stensen var i Paris,” Fund og Forskning 16 (1969), p. 43–52, and R. Andrault, “Introduction,” in N. Sténon, Discours sur l’anatomie du cerveau, ed. R. Andrault (Paris: Classiques Garnier, 2009); on Steno and the English, see F.H.L. Poynter, “Steno and the Royal Society of London,” in Steno and Brain Research in the Seventeenth Century, ed. G. Scherz (Oxford: Pergamon Press, 1968), p. 273–280; D.R. Rome, “Nicolas Sténon et la ‘Royal Society of London’,” Osiris 12 (1956), p. 244–268.
[3] See V. Maar (ed.), Holger Jacobæus’ Rejsebog (København: Gyldendal, 1910). The academic travels of seventeenth-century Danes have been studied in some detail in O. P. Grell, “Like the bees, who neither suck nor generate their honey from one flower”: the significance of the peregrinatio academica for Danish medical students of the late sixteenth and early seventeenth centuries,” in Centres of Medical Excellence? Medical Travel and Education in Europe 1500-1789, ed. O. P. Grell, A. Cunningham, and J. Arrizabalaga (Aldershot: Ashgate, 2010), pp. 171–189; Ole Peter Grell, “In search of true knowledge: Ole Worm (1588-1654) and the New Philosophy,” in Making Knowledge in Early Modern Europe: Practices, Objects and Texts 1400-1800, ed. P. Smith and B. Schmidt (Chicago: Chicago University Press, 2008), 214–232. See also some pages in the family history published by one of Jacobæus’s descendants in 1931 which includes a summary of Bartholin’s De peregrinatione medica ad Oligerum Iacobæum, nepotem suum, et filios Casparum Bartholinum, Christophorum Bartholinum of 1674 (H. Jacobæus, En Lærd Families Liv og Livsvilkår i det 16. og 17. Aarhundrede, København : Gyldendalske Boghandel, Nordisk Forlag, 1931, p. 64 ).
[4] See V. Maar, “Indledning,” in Holger Jacobæus’ Rejsebog, p. i-xv; G. Scherz, Biography of Nicolaus Steno, trans. in Kardel and Maquet, Nicolaus Steno, p. 337, 405–407.
[5] Incidentally, it appears that, much later in 1685 while in Hamburg, Steno tried again to convert Jacobæus, but in vain; see Steno to Cosimo III, 9 (19) September 1685, in Niels Stensen’s Korrespondance [København: C. A. Reitzels Forlag, 1987], vol. II, p. 691 incl. note 2.
[6] N. Steno, Auctor enumerat suas culpas et de ipsis petit misericordiam a Deo [later than 30 May 1685], ed. V. Maar, in “To uudgivne Arbejder af Nicolaus Steno fra Bibliotheca Laurenziana,” Oversigt over Det Kgl. Danske Videnskabernes Selskabs Forhandlinger 4 (1910), p. 313–327, here p. 317: “I wanted to publish my writings on natural things [Desideravi publicationem meorum scriptorum de rebus naturalibus.]”
[7] A. Garboe, Niels Stensens geologiske Arbejders Skæbne (København: C. A Reitzels Forlag, 1948); Axel Garboe, “Niels Stensen’s (Nicolaus Steno’s) lost geological manuscript,” Meddelelser fra Dansk Geologisk Forening 14 (1960), p. 243–246.
[8] See e.g. Scherz, Biography, p. 337.
[9] See V. Maar, “Indledning,” p. x–xi.
[10] G. W. Leibniz, Otium hanoveranum; sive, Miscellanea, ex ore & schedis illustris viri … Godofr. Guilielmi Leibnitii, ed. J . F. Feller (Lipsiae: impensis J. C. Martini, 1718), Text n° XIVIII: “Memoire donné à un Voyageur du Nord,” p. 97: “Monsieur Otto Sperling, Historiographe de Danemark, avoit dessein de donner la vie de Cranzius, & je luy donnai quelque notice pour cela. Se cette vie est achevee, elle meriteroit d’etre donne au public. / J’ay appris, que feu Mr. Stenonis, se dechargeant de la litterature profane, chargea Monsieur Oliverius [i.e. Oligerus] Jacobæus, Medecin Danois, de pousser et de poursuivre ses pensées sur la Geographie naturelle, et les changemens physiques de la surface de la terre. Je voudrois bien savoir, si ce savant homme y travaille effectivement.” Cit. in Garboe, Niels Stensen’s Geologiske Arbejders Skæbne, p. 17; also cited in Scherz, Biography, p. 407.
[11] Otto Sperling (1634–1715), lawyer and historiographer, not to be confused with his more famous father, the physician Otto Sperling (1602–1681). Sperling the younger studied in 1652–1656 in Helmstedt under Hermann Conring, then in Leiden (studiosus politicus) in 1659, and in France and England in 1661. Spent a good portion of his career as a jurist in Hamburg, but also some time in Copenhagen in 1670–1673, and was even employed for a while in Paris, at the library of Colbert; became professor of history and law in Copenhagen in 1692, was dismissed in 1697 then reemployed in 1701. Sperling’s substantial extant archives include, among many other things, a three-volume biography in manuscript of the Hamburg historian of the Germanic peoples, Albrecht Kranz (1448–1517). See H. Ilsøe, “ Sperling – Historiker.” Dansk Biografisk Leksikon, in ed. S. Cedergreen Bech (ed.), Dansk Biografisk Leksikon, 16 vols. (1679–1984)], now online on lex.dk. Retreived 13. July 2025, URL : https://biografiskleksikon.lex.dk/Otto_Sperling_-_historike.
[12] Leibniz to Chr. A. Walter, Autumn 1683, A III, iv, p. 65–66: “Comme je sçay que vous avés tousjours esté curieux et que je ne sçaurois quitter cette même humeur, je prends la liberté de vous demander des nouvelles de quelques curiosités de Copenhague. Mons. Stenonis m’a conté autres fois qu’il avoit donné ses Manuscrits touchant les connoissances naturelles à quelques amis capables des pousser, depuis qu’il a renoncé à cette sorte d’estudes et si je ne trompe pas il avoit donné les Geographiques (touchant la constitution et les changemens physiques du globe de la terre, sur quoy il avoit des meditations importantes) à Mons. Oligei Jacobaeus, et les Anatomiques à Mons. Caspar Bartholin. Ayés la bonté Monsieur de vous en informer, particulierement de celles qui touchent le globe de la terre, car il pretend ce que me semble de prouver par des raisons physiques, qu’il y a eu un deluge universel, et quantité de belles choses conformes à l’écriture Ste.” Leibniz exchanged some 14 letters with Walter between 1676 and 1683 (10 from Walter, 4 from Leibniz).
[13] Cit. in Garboe, “Niels Stensen’s lost geological manuscript,” p. 244-245 (including a photographic reproduction of the original Latin Letter).
Research for this blog post was funded by the European Union (NOTCOM, ERC Advanced Grant no. 101052433). Views and opinions expressed are solely those of the author and do not necessarily reflect the views and opinions of the European Union nor of the ERC. Neither the European Union nor the granting authority can be held responsible for any of the views expressed herein.

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