Editing Nicolas Steno (section)

== Scientific contributions ==

=== Anatomy ===
During his stay in Amsterdam, Steensen discovered a previously undescribed structure, the "''[[Parotid duct|ductus Stenonis]]''" (the duct of the [[Parotid gland|parotid salivary gland]]) in sheep, dog and rabbit heads. A dispute with Blasius over credit for the discovery arose, but Steensen's name remained associated with this structure known today as the [[parotid duct|Stensen's duct]].{{sfnp|Kermit|2003}} In Leiden, Steensen studied the boiled [[heart]] of a cow, and determined that it was an ordinary [[muscle]].{{sfnp|Tubbs et al.|2010}}{{sfnp|Andrault|2010}} and not the center of warmth as [[Galenus]] and Descartes believed.<ref>Kooijmans (2007), p. 45.</ref> In [[Florence]], Steensen focused on the [[muscular system]] and the nature of [[muscle contraction]]. He became a member of [[Accademia del Cimento]] and had long discussions with [[Francesco Redi]]. Like [[Vincenzo Viviani]], Steensen proposed a geometrical model of muscles to show that a contracting muscle changes its shape but not its [[volume]].{{sfnp|Kardel|1990}}{{sfnp|Kardel|1994|p=1}}
{{clear left}} Steensen was the first to describe the [[lateral line]] system in fish.{{citation needed|date=February 2024}}

=== Paleontology ===
{{See also|History of paleontology}}
[[File:Steensen - Elementorum myologiae specimen, 1669 - 4715289.tif|thumb|upright|''Elementorum myologiae specimen'': Illustration from Steensen's 1667 paper comparing the teeth of a shark head with a fossil tooth.]]
In October 1666, two fishermen caught a huge female [[shark]] near the town of [[Livorno]], and [[Ferdinando II de' Medici]], Grand Duke of Tuscany, ordered its head to be sent to Steensen. Steensen [[dissection|dissected]] the head and published his findings in 1667. He noted that the [[Shark tooth|shark's teeth]] bore a striking resemblance to certain stony objects, found embedded within rock formations, that his learned contemporaries were calling ''glossopetrae'' or "tongue stones". Ancient authorities, such as the [[Ancient Rome|Roman]] author [[Pliny the Elder]], in his ''[[Natural History (Pliny)|Naturalis Historia]]'', had suggested that these stones fell from the sky or from the [[Moon]]. Others were of the opinion, also following ancient authors, that [[fossil]]s naturally grew in the rocks. Steensen's contemporary [[Athanasius Kircher]], for example, attributed fossils to a "lapidifying virtue diffused through the whole body of the geocosm", considered an inherent characteristic of the earth – an [[Aristotelianism|Aristotelian]] approach. [[Fabio Colonna]], however, had already shown by burning the material to show that ''glossopetrae'' were organic matter (limestone) rather than soil minerals,<ref>[https://web.archive.org/web/20070318025357/http://www.musei.unina.it/Paleontologia/3.2.3.htm Breve storia della paleontologia], internet site of Centro dei Musei di Scienze Naturali, university of Naples Retrieved 10 January 2012.</ref> in his treatise ''De glossopetris dissertatio'' published in 1616.{{sfnp|Abbona|2002|loc=Geologia |ps=: Colonna had been schooled in the collection of [[Ferrante Imperato]], apothecary and ''virtuoso'' of Naples, who published his natural history notes in 1599.}}<ref>{{cite journal|doi=10.1080/08912963.2013.825257|title='The vain speculation disillusioned by the sense': The Italian painter Agostino Scilla (1629–1700) called 'The Discoloured', and the correct interpretation of fossils as 'lithified organisms' that once lived in the sea|journal=Historical Biology|volume=26|issue=5|pages=631–651|year=2014|last1=Romano|first1=Marco|bibcode=2014HBio...26..631R |s2cid=129381561}}</ref> Steensen added to Colonna's theory a discussion on the differences in composition between glossopetrae and living sharks' teeth, arguing that the chemical composition of fossils could be altered without changing their form, using the contemporary [[Corpuscularianism|corpuscular theory of matter]].

Steensen'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 Steensen's interest included not only fossils, as we would define them today, but minerals, crystals, encrustations, veins, and even entire rock layers or [[stratum|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. This book was his last scientific work of note.{{sfnp|Garrett Winter|1916|p=182}}{{efn|[[Leibnitz]] came to know and esteem Steensen in Hannover and expressed deep regrets that he had abandoned his earlier studies.{{sfnp|Garrett Winter|1916|p=182.}} }} Steensen was not the first to identify fossils as being from living organisms; his contemporary [[Robert Hooke]] also argued that fossils were the remains of once-living organisms.<ref>{{cite book|last=Rudwick|first=Martin J.S.|author-link=Martin J. S. Rudwick|title=The Meaning of Fossils|year=1976|publisher=The University of Chicago Press|page=54}}</ref>

=== Geology and stratigraphy ===
[[File:Steno De Solido Dissertationis Prodromus 1669.jpg|thumb|upright|''De solido intra solidum naturaliter contento dissertationis prodromus'' (1669)]]
{{Main|law of superposition|principle of original horizontality|principle of lateral continuity}}
Steensen, in his ''Dissertationis prodromus'' of 1669 is credited with four of the defining principles of the science of [[stratigraphy]]. His words were:
# the [[law of superposition]]: "At the time when a given stratum was being formed, there was beneath it another substance which prevented the further descent of the comminuted matter and so at the time when the lowest stratum was being formed either another solid substance was beneath it, or if some fluid existed there, then it was not only of a different character from the upper fluid, but also heavier than the solid sediment of the upper fluid."
# the [[principle of original horizontality]]: "At the time when one of the upper strata was being formed, the lower stratum had already gained the consistency of a solid."
# the [[principle of lateral continuity]]: "At the time when any given stratum was being formed it was either encompassed on its sides by another solid substance, or it covered the entire spherical surface of the earth. Hence it follows that in whatever place the bared sides of the strata are seen, either a continuation of the same strata must be sought, or another solid substance must be found which kept the matter of the strata from dispersion."
# the [[principle of cross-cutting relationships]]: "If a body or discontinuity cuts across a stratum, it must have formed after that stratum."<ref>{{cite book |last=Steno |first=Nicolas |url=https://archive.org/details/cu31924012131458 |title=Nicolas Steno's Dissertation Concerning a Solid Body Enclosed by Process of Nature within a Solid: An English Version with an Introduction and Explanatory Notes |date=1916 |publisher=New York, Macmillan; London, Macmillan |translator-last1=Winter |translator-first1=John}} Pages 229–230.</ref>
These principles were applied and extended in 1772 by [[Jean-Baptiste L. Romé de l'Isle]]. Steensen's ideas still form the basis of stratigraphy and were key in the development of [[James Hutton]]'s theory of [[James Hutton#Search for evidence|infinitely repeating cycles]] of seabed deposition, uplifting, erosion, and submersion.{{sfnp|Brookfield|2004|p=116}}

=== Crystallography ===
{{further|topic=crystallographic indices|Crystal system}}
Steensen gave the first accurate observations on a type of crystal in his 1669 book ''De solido intra solidum naturaliter contento'' (the ''Dissertationis prodromus'').{{sfnp|Kunz|1918}} The principle in [[crystallography]], known simply as ''Steensen's law'', or the [[law of constancy of interfacial angles]] or the ''first law of crystallography'',<ref>{{cite journal | last1 = Molčanov | first1 = K. | last2 = Stilinović | first2 = V. | year = 2014 | title = Chemical Crystallography before X-ray Diffraction | journal = Angew. Chem. Int. Ed. | volume = 53 | issue = 3| pages = 638–652 | doi = 10.1002/anie.201301319 | pmid = 24065378 }}</ref> states that the angles between corresponding faces on crystals are the same for all specimens of the same mineral. Steensen's seminal work paved the way for the [[law of rational indices]] of French mineralogist [[René-Just Haüy]] in 1801.{{sfnp|Kunz|1918}}<ref>{{cite web |title=Stephen A. Nelson (Tulane University) Introduction to Earth Materials |url=http://www.tulane.edu/~sanelson/eens211/introsymmetry.pdf |access-date=11 January 2012}}</ref> This fundamental breakthrough formed the basis of all subsequent inquiries into [[crystal structure]].