Nicolas Steno (Danish: Niels Stensen; latinized to Nicolaus Stenonis) (January 10, 1638 - November 25, 1686) was a pioneer in both anatomy and geology. Already in 1659 he decided not to accept anything simply written in a book, instead resolving to do research himself. He is considered the father of geology and stratigraphy.
Fair is what we see, Fairer what we have perceived, Fairest what is still in veil
On instigation of Thomas Bartholin Steno first travelled to Rostock, then to Amsterdam and studied anatomy under Gerard Blasius, focusing again on the Lymphatic system. Steno discovered a previously undescribed structure, the "ductus stenonianus" (the duct of the parotid salivary gland) in sheep, dog and rabbit heads. A dispute with Blasius over credit for the discovery arose, but Steno's name is associated with this structure. Within a few months Steno moved to Leiden. There Steno met the students Jan Swammerdam, Frederik Ruysch, Reinier de Graaf, Franciscus de le Boe Sylvius, a famous professor, and Baruch Spinoza. Also Descartes was publishing on the working of the brain, and Steno did not think his explanation of the origin of tears was correct. Steno studied the heart, and found out it was an ordinary muscle.
He travelled to Saumur were he met Melchisédech Thévenot and Ole Borch. Steno travelled to Montpellier, where he met Martin Lister and William Croone, who introduced his work to the Royal Society. In Pisa he met the Grand Duke of Tuscany, who supported arts and science. Steno was invited to live in the Palazzo Vecchio, in return he had to gather a Cabinet of curiosities. Steno first went to Rome and met Alexander VII and Marcello Malpighi. As an anatomist in the hospital Steno focused on the muscular system and the nature of muscle contraction. He also became a member of Accademia del Cimento in Florence. Like Vincenzio Viviani Steno used geometry to show that a contracting muscle changes its shape but not its volume.
Steno's work on shark teeth led him to the question of how any solid object could come to be found inside another solid object, such as a rock or a layer of rock. The "solid bodies within solids" that attracted Steno's interest included not only fossils, as we would define them today, but minerals, crystals, encrustations, veins, and even entire rock layers or strata. He published his geologic studies in De solido intra solidum naturaliter contento dissertationis prodromus, or Preliminary discourse to a dissertation on a solid body naturally contained within a solid in 1669. Steno was not the first to identify fossils as being from living organisms; his contemporaries Robert Hooke and John Ray also argued that fossils were the remains of once-living organisms.
Steno, in his Dissertationis prodromus of 1669 is credited with three of the defining principles of the science of stratigraphy: the law of superposition: "...at the time when any given stratum was being formed, all the matter resting upon it was fluid, and, therefore, at the time when the lower stratum was being formed, none of the upper strata existed"; the principle of original horizontality: "Strata either perpendicular to the horizon or inclined to the horizon were at one time parallel to the horizon"; the principle of lateral continuity: "Material forming any stratum were continuous over the surface of the Earth unless some other solid bodies stood in the way"; and the principle of cross-cutting discontinuities: "If a body or discontinuity cuts across a stratum, it must have formed after that stratum. These principles were applied and extended in 1772 by Jean-Baptiste L. Romé de l'Isle. Steno's landmark theory that the fossil record was a chronology of different living creatures in different eras was a sine qua non for Darwin's theory of natural selection.
Another principle, known simply as Steno's law, or Steno's law of constant angles, states that the angles between corresponding faces on crystals are the same for all specimens of the same mineral, a fundamental breakthrough that formed the basis of all subsequent inquiries into crystal structure.
Steno travelled to Hungary, Austria and in Spring 1670 he arrived in Amsterdam. There he met with old friends Jan Swammerdam, Reinier de Graaf. With Anna Maria van Schurman and Antoinette Bourignon he discussed scientific and religious topics. It is not sure if he met Nicolaes Witsen, but he did read his book on shipbuilding. In 1671 he accepted a post in Copenhagen, but promised Cosimo III de' Medici he would return when he would be appointed as the tutor of Ferdinando III de' Medici. In 1675 Steno was back in Florence and ordained a priest. Athanasius Kircher expressly inquired to the reason. Steno had left science and became one of the leading figures in the Counter-Reformation.
In the year after he was made bishop, and probably involved in banning the publications by Spinoza. He came on a mission in Lutheran North on an invitation by John Frederick, Duke of Brunswick-Lüneburg. There he regularly had talks with Gottfried Leibniz, the librarian; the two argued about Spinoza and his letter to Albert Burgh, then Steno's pupil. Leibniz recommended a reunification of the churches. Steno worked from the city of Hannover until 1680. Steno accepted a position in Münster (Church Saint Liudger) while the new prince-elector Ernest Augustus, Elector of Hanover was a Protestant. Earlier his wife Sophia of Hanover had made fun of Steno's piousness. He sold his bishop's ring and cross to help the needy.
In 1684 Steno moved to Hamburg, after an argument about un-churchlike character of the election of the new bishop, c.q. Maximilian Henry of Bavaria. There he became involved anew in the brain and the nerve system by an old friend Dirck Kerckring. Steno was invited to Schwerin, when it became clear he was not accepted in Hamburg. Steno dressed like a poor man in an old cloak. He drove in an open carriage in snow and rain. Living four days a week on bread on beer he became emaciated. When Steno had fulfilled his mission, years with difficult tasks, he wanted go back to Italy. Before he could return Steno became severely ill with his belly swelling daily. Steno died after days of suffering. His corpse was shipped by Kerckring to Florence and buried in the Basilica of San Lorenzo close to his protectors, the De' Medici family. In 1953 his grave was discovered, and the corpse (without the missing skull) was reburied after a procession throught the streets of the city.