also known as Nicolaus Steno
b. Copenhagen, Denmark, 1/11 January 1638; d. Schwerin, Germany 25 November/5 December 1686)
anatomy, geology, mineralogy.
Stensen was the son of Sten Pedersen, who came from a family of preachers and was a goldsmith. After graduating from the Liebfrauenschule, Stensen entered the University of Copenhagen in 1656. There he studied medicine and came under the special influence of Simon Paulli and Thomas Bartholin. The customary study journey took him at the end of March 1660 to Amsterdam and, on 27 July for his matriculation, to the University of Leiden, from which, after three years of diligent research, he was called home because of the death of his stepfather.
The University of Copenhagen failed to enlist Stensen’s services, and so he went to Paris: he is known to have been there as late as November 1664 and to have received on 4 December his M.D. from the University of Leiden in absentia. After a fruitful year in the circle of Thévenot, the king’s chamberlain, Stensen went in the autumn of 1665 to Montpellier: and from there he went to Pisa, where he stayed until the beginning of March 1666. He remained in Tuscany until July 1668, mostly at the court of Grand Duke Ferdinand II in Florence.
Although he came from a deeply religious Lutheran family, Stensen became a convert to Catholicism on All Souls’ Day 1667 during a period of research in anatomy and geology. This research was interrupted, probably by a summons to Denmark, from August 1668 to June 1670. Upon his return to Florence, Stensen again worked in Tuscany, exploring two alpine grottoes at Lake Garda and Lake Como for the Accademia del Cimento.
Following a call to return to Denmark as royal anatomist, Stensen arrived at Copenhagen on 3 July 1672. Here, mostly for a circle of interested friends, he held a series of anatomical demonstrations. But he left his native city on 14 July 1674 to return to Florence, where he was consecrated a priest, probably in the middle of April 1675, and where he worked for two years as educator and tutor of the crown prince. Upon the invitation of Duke Johann Friedrich of Hannover, he went to Rome, where he was appointed apostolic vicar of northern missions by Pope Innocent XI on 21 August 1677 and was consecrated titular bishop of Titiopolis on 19 September. Until the end of June 1680, he ministered to the scattered remnants of Catholicism in northern Germany, Denmark, and Norway. Then after the death of the duke, he was appointed assistant bishop of Münster in Westphalia, where he was very active. On 1 September 1683 he left the city in protest against the simoniac election of the bishop’s successor. After two years of apostolic activity in Hamburg and Schwerin, he died in acute pain from gallstones.
Two educational influences upon Stensen’s youth deserve special attention. Since his father’s goldsmith shop was near the Round Tower, his scientific interest may have been directed at an early age into technical-mathematical channels to which he wished to return even in the midst of his first period of biological investigations in Leiden. He was interested in minerals and metals; in lenses and light refraction; and in telescopes, microscopes, and thermoscopes. Thomas Walgesten, the inventor of the laterna magica, belonged to the circle of his acquaintances. Stensen, of course, knew the medical authors Thomas Bartholin, Pierre Borel, Henricus Regius, Paracelsus, Helmont, and Santorio. Stensen’s physical-mathematical interests are indicated by his reading not only the works of Galileo (Sidereus nuncius) and Kepler (De nive sexangula ) but also those of Gassendi, Clavius, Gaspar Schott, Snel, and Varenius. Stensen had a precocious desire for methodically founded knowledge, and he was critical of analogies and purely authoritarian statements. He also asked for frequent observations and correct conclusions, and he declared himself in favor of Descartes’s method in order to secure the greatest possible certainty. Stensen’s writings also contain many passages that show a deeply religious nature and a highly ethical character.
During the second half of his life, in which he attained the highest fame and then–for the sake of God and of human souls–renounced his scientific research, there can be differentiated, both in time and in subject matter, four great periods of research. Each period began with almost accidental individual observations but led to an abundance of important discoveries and basic laws, many of which were recognized only in later centuries.
The first of these periods was devoted to the glandular and lymphatic system. In April 1660, three weeks after his arrival at Amsterdam, where he studied under the direction of Gerhard Bläes (Blasius), Stensen made his first known discovery: while dissecting the head of a sheep, he found the duct of the parotid gland (Stensen’s duct), which is a principal source of saliva for the oral cavity.
In Leiden, then the most important university on the Rhine, Stensen sought contact with the two leading medical professors: Johannes van Horne, who independently of Pecquet had discovered the chief thoracic lymph passage, and Franciscus Sylvius, famous as an iatrochemist and for his studies on the brain. A warm and stimulating friendship with Jan Swammerdam also began in Leiden. Soon after Stensen’s arrival, van Horne demonstrated on humans the course of the parotid duct and declared it to be Stensen’s discovery, although Blasius, in his Medicina generalis (1661), not only claimed it for himself but incited his friends to slander Stensen, his former student. There ensued a long quarrel that Stensen settled both objectively and devastatingly in his Apologiae prodromus (1663).
The controversy spurred Stensen to the further investigation of the glands. He wrote: “I owe much to the famous man Blasius because he not only gave me cause to assert my property rights, but also to discover other new things.”
The glands and lymph vessels were then a new and exciting subject for investigation. In 1622 Aselli had demonstrated the lacteal vessels in the mesentery of a dog; in 1642 Johann Georg Wirsung had shown the excreting duct of the pancreas; and in 1651 Pecquet had demonstrated the cisterna chyli and its continuation, the thoracic lymph duct; he also had realized that the latter poured its contents into the veins. In 1653 Thomas Bartholin demonstrated the thoracic lymph passage and the lymphatic system in humans. He also showed that the lymph vessels connecting the liver to the thoracic duct carried lymph away from the liver, thereby throwing doubt on the Galenic doctrine that blood originated in the liver. When Thomas Wharton published his systematic presentation of the contemporary theory of glands in his Adenographia (1656), he announced the discovery of the duct of the submaxillary salivary gland; he also designated the brain and tongue as glands.
In contrast, Stensen very soon advanced from his “little discovery,” as he called his first one, to a basic understanding of the whole glandular lymphatic system, which he counted among the most sublime artifices of the Creator. Without changing the names of the conglomerate and conglobate glands, the terms by which Sylvius had already distinguished the anatomical form of the real glands from that of the lymph nodes, Stensen distinguished them according to their function. Arguing against such contemporaries as Bils, Anton Deusing, and Everaertz, on the basis of his observations Stensen stated in his Leiden dissertation (1661):
I gather from this that the saliva consists of the fluid secreted in the oral glands from the arterial blood which is carried through the lymph ducts with the aid of the Spiritus animales [a term then used for the nerves] into the mouth and the closely adjoining muscles, but that the round or conglobate glands in the proximity carry the lymphs received from the outer parts back to the veins so that it becomes mixed with the blood streaming back to the heart.
This discovery led Stensen to consider every fluid in the body as a glandular secretion. He then found a series of glands furnishing fluid to each of the body cavities. He likewise sought the afferent and efferent ducts of secretion. Stensen still used the name “lymph” for all watery glandular secretions, because he was not yet able to differentiate between them and to specify them chemically and physiologically.
In the course of this basic research Stensen presented in his Leiden dissertation new discoveries of glands in the cheeks; beneath the tongue; and in the palate, whose structure of veins, arteries, nerves, and lymph vessels he also described. In his Observationes anatomicae (1662), dealing with his new discoveries concerning the glands, he described the lachrymal apparatus in great detail. Stensen determined the purpose of the lachrymal fluid–to facilitate the movement and cleansing of the eyelids on the same principle that applied to the saliva and the mucous membrane of the intestinal canals. He grouped the afferent and efferent lachrymal ducts around the tear gland proper and what was then called glandula lacrimalis, in the inner eye corner. The moisture of the nose led him in this connection, to the discovery of the nasal glands. Stensen considered the possibility that the moisture necessary for the nose could come from the ears through the eustachian tubes, and from the eyes through the nasal duct, but decided that the principal source was the nasal glands. He assumed that this fluid disappeared again through the nostrils and also through an opening to the gullet, the ductus nasopalatini, also called ductus Stenoniani.
In his survey De musculis et glandulis (1664) Stensen enumerated all his new observations and individual discoveries, especially those he had made during the first half of his stay in Leiden: earwax duct, ducts of the cheek glands, the smaller gland ducts under the tongue, the glandular ducts of the palate, the glandular ducts of the epiglottis, the nasal gland, the nasal gland peculiar to sheep, the passage from the eyelids to the nose, the lachrymal ducts, and the gland ducts that lubricate the exterior surface of the ray. In 1673 Stensen found, independently of Peyer, the accumulations of lymph follicles in the small intestine (named for Peyer), but published his findings four years later.
The second period of research began with a challenge to the traditional overestimation of the heart: “One has glorified the heart as the sun, even as the king while upon closer examination, one finds nothing but a muscle,” which was directed not only against Aristotle, who saw the heart as the seat of the soul, the source of life, and the central organ of all sensation and motion, but also against Galen, who, following the authority of Plato, assigned the life forces of blood motion and heat distribution to the left ventricle. Even Harvey, who first recognized the purely muscle activity of the heart in maintaining the circulation of the blood, did not abandon the idea of a vital warmth within the heart, or did so only very late.
In a letter of 26 August 1662, Stensen told Thomas Bartholin how fascinated he was by the independent motions of the vena cava, which continued even after the stopping of the heartbeat; this stimulated Stensen to make many investigations of the heart and respiratory organs. On 5 March he had spoken of a careful investigation of the heart musculature, and on 30 April he had stated: “As to the substance of the heart, I think I am able to prove that there exists nothing in the heart that is not found also in a muscle, and that there is nothing missing in the heart which one finds in a muscle.”
De musculis et glandis (1664) shows an abundance of new observations and discoveries concerning the anatomy and physiology of individual muscle, and the triangularis, which leads from function of the intercostal muscles, the sacrolumbar muscle, and the triangulararis, which leads from the bony end of the true ribs to the central line of the sternum. He described the role of the diaphragm and several other muscles during respiration; classified the tongue as a muscle; and also described the temporal muscle, and the muscle layer of the esophagus, which has its fibers arranged spirally.
From this research Stensen drew comprehensive conclusions concerning the structure of the muscles: that in each muscle there are arteries, veins, fibers and fibrils, nerves, and membranes; that each muscle fiber ends in a tendon on both sides; that no muscle tissue is a parenchyma (caro) but consists instead of closely woven fibers; and that the contractility lies in the muscle substance proper. He then applied all his finding to the heart and proved its muscle structure from both positive and negative evidence. He stated that the heart possesses all the characteristics of a muscle structure and that it is neither the seat of joy nor the source of the blood or of the spiritus vitales. The automatic movement, independent of the will, is shared by the heart with other muscles. The findings were new, and even ten years later Bartholin, in a new edition of his Institutions anatomicae (1611), did not accept them. Croone revised his De ratione motus musculorum (1664) according to Stensen’s findings in the second edition (1670).
The controversy over his views caused Stensen, during his first year in Italy (1666/1667) to publish his Elementorum myologiae specimen, which dealt chiefly with the questions: Does the muscle increase in size during contraction? Are hardness and swelling of the muscle signs of an increase in volume? These were acute questions at the time, when even Borelli, one of the leading members of the Accademia del Cimento, still believed that swelling was caused by the influx of nerve fluid. Stensen first provided clear concepts and a clearcut terminology of the parts of the muscle. Then he characterized the individual muscle fiber and the muscle itself as a parallepiped bordered by six parallelograms. In the second part of the Elementorum he dealt with objections against the new knowledge about muscles, and lamented the insufficient knowledge of the muscle fluid. Later, Stensen (before the theory of irritability proclaimed by Haller) discovered that a muscle contraction can also result from direct stimulation of the muscle.
Stensen’s muscle research was also a symptom of his philosophical-religious struggle. At the turn of 1662/1663 he had wanted to abandon anatomy for mathematics and physics, a wish probably fostered by the spirit of the times and by his desire for certainty. The need for quantitative knowledge was indicated by Stensen’s early enthusiasm for Descartes’s method of attaining certainty. During his years in Leiden, Stensen became friendly with Spinoza, whose rationalism may have influenced Stensen so strongly that his Christian belief was endangered. His discovery of the muscle structure of the heart showed him the fallacy of the Cartesian view of the heart as a hearth of fire and made him skeptical of their whole seemingly firmly anchored geometrical philosophy. As he admitted later to Leibniz: “If these gentlemen have been so mistaken with material things which are accessible to the senses, what warranty can they offer that they are not mistaken when they talk about God and the soul?”
The third period of research extended from 1665 to 1667, the last great anatomical-physiological period of his life. The period can be divided into three parts: brain anatomy, embryology, and comparative anatomy.
Stensen’s study of brain anatomy was confined almost entirely to his Discours . . . sur I’ anatomie du cerveau (1669), which he presented in Paris to Thévenot’s circle, among whom were many Cartesians. Stensen was stimulated to undertake his brain studies not only by his teacher, the brain anatomist Sylvius, but also by Descartes’s Traité de l’homme. Vigorously but tactfully, Stensen opposed Descartes’s mechanical theory and revealed his anatomical errors, refuting especially his theory concerning the epiphysis. According to Stensen, the epiphysis could not possibly carry out the slightest motion and thereby contribute to one’s actions; whereas the Cartesian view was that it inclined itself to one side and then to the other side. In the Discours Stensen calls for a sober terminology and proposes new methods of dissection and the preparation of specimens. Stensen demands that the investigation trace the course of the brain fibers and that the investigator strive for a secure knowledge of the anatomical parts before interpreting their functions. In recent times his drawings of the brain have shown that he had a very rich knowledge of its anatomy.
From 1667 to 1669 Stensen contributed two concepts about the ovum and the ovary, oviduct, and uterus. The ovaries were considered to be testes muliebres, a type of semen producer. In a recently hatched chick Stensen discovered the oviduct and recognized that it was a canal destined to conduct the yolk directly into the intestine. In the Elementorum Stensen says that since he had found the true ova in the female testes, he concluded that they were really ovaries. Johannes Peter Müller credited Stensen with a discovery made by Aristotle but then forgotten: that in the so-called smooth sharks (Mustelus laevis) the eggs are not deposited, but the embryos remain connected to the uterus by a placenta, similar to that of mammals. Stensen’s embryological observations were not published until 1675, but he had communicated them to De Graaf and Swammerdam. Therefore, the Royal Society of London, in the priority dispute concerning the procreative organs, assigned the credit to Stensen.
Among Stensen’s unpublished observations are those on rays and sharks. He established the mucous canal system of these fishes and recognized the significance of the spiral fold in the intestine as a substitute for its greater length in other creatures. He also observed the eyeball stalk, the optical nerve, and the crossing of the optic nerves.
The technical side of Stensen’s research was highly developed. He employed simple but effective means, such as the induction of bristles into the gland ducts or the expansion of vessels by inflation. It is not known to what extent he used the microscope, but he knew the optical experts of his time and such microscopists as Swammerdam and Malpighi. He was also a skilled draftsman. His diagram of the blood circulation, which for the first time revealed the heart as two relatively independent hearts or pumps, enabled his pupil Caspar Bartholin, Jr., to develop further the concept of circulation.
The fourth and greatest period of Stensen’s research began in Florence at the end of October 1666, when he received the head of a gigantic Carcharodon rondeletii that had been caught near Leghorn. He made acute observations of its skin, its canals, the brain and nerves, the Lorenzinian ampullae, and the eyes. The rows of pointed teeth in the mouth, however, led him to a thorough study of their number and substance and also placed immediately before him the question of the relation of these teeth to the so-called glossopetra or tongue-stones, which were common on Malta and were considered lapides sui generis. Stensen concluded that they were fossil shark’s teeth. This led to his paleontological, geological, and mineralogical discoveries.
Scarcely eighteen months later his great work, the Prodromus, which outlines the principles of modern geology, was printed. The book presents only the outlines of a discussion, yet almost every sentence or paragraph contains new insights.
After an introductory methodological discussion, Stensen states his purpose: “to find, in the case of a body possessed of a certain shape and produced on the basis of natural laws, the proofs in the body itself which reveal the site and the type of its origin.” There follow three important sections: the first concerning the relationship in time between the enclosing body and the body enclosed; the second, the determination of the site and origin of a solid body; and the third. the role of fluids in nature.
In the third section Stensen states such important findings as the fundamental difference between inorganic bodies formed by apposition, and organic bodies formed by apposition, and organic bodies formed by internal susception. In the third part the individual enclosing and enclosed bodies are considered. In the central section on geological strata Stensen presents his sediment theory, the time sequence and material of the strata, and data on the site of the stratification. After general observations concerning the effects on the strata of the changes of form through the forces of water and fire, there follows a special section on the origin of mountains. He discusses the sites of ores and minerals and includes an interesting section on crystals. At the end of the section, in drawings and two brief sentences, he states the law of the constancy of crystallic angles. The fourth main part of the work offers an application of the new finding to the geology of Tuscany, which is summarized in six stages of development and illustrated with six drawings. Finally he suggests the possible adaptation of all new findings to the generally prevailing world picture. Although Stensen introduced the concept of chronology and the history of the earth, he had little awareness of the actual duration of geological time.
A glance back to the first main part of the Prodromus shows the value of Stensen’s methodological directives. He demanded that in the solution of a problem the questions connected with it be considered, that facts be distinguished from assumptions, and that the individual result be examined in connection with the history of science.
In the preface to his last great dissection of a female body (1673) Stensen states the spiritual side of his point of view. He calls the anatomist the index finger of God, addresses science as the servant of life, and declares himself a member of three realms (nature, mind, and faith) and does so in the name of beauty.
I. Origianl Works. Collected works of Stensen’s writings are Nicolai Stenonis opera philosophica, Vilhelm Maar, ed., 2 vols. (Copenhagen, 1910), which includes the scientific works; Nicolai Stenonis opera theologica . . ., Knud Larsen and Gustav Scherz, eds. (Copenhagen, 1941, 1947), the theological and ascetical writings; Nicolae Stenonis epistolae et epistolae ad eum datae . . . , Gustav Scherz, ed., 2 vols. (Copenhagen-Fribourg, 1952), which includes Stensen’s correspondence with an introduction on the correspondents, notes. and documents; and Pionier der Wissenschaft, Niels Stensen in seinen Schriften (Copenhagen. 1963), with a short biography and selected texts with introductions.
Stensen’s most important writings include Observationes anatomicae, . . . (Leiden, 1662), which consists of four treatises, including Stensen’s Disputatio anatontica de glandalis oris . . . (1661); De musculis et glandulis (Copenhagen, 1664), which includes two letters: “De anatome rajae epistola” and “De vitelli in intestina pulli transitu epistola"; Elementorum myologiae specimen (Florence, 1666/1667), also published as Bibliotheca anatomica (London, 1709–1714), an abridged English version; Discours . . . sur I’anatomie du cerveau (Paris, 1669), also published in G. Scherz, Nicolaus Steno’s Lecture on the Anatomy of the Brain (Copenhagen, 1965); and De solido intra solidum naturaliter contento dissertationis prodromus (Florence, 1669), trans. by H. O[Idenburg], The Prodromus to a Dissertation Concerning Solids Naturally Contained Within Solids . . . (London, 1671), and by John G. Winter, The Prodromus of Nicolas Steno’s Dissertation Concerning a Solid Body Enclosed by Process of Nature Within a Solid (New York, 1916).
See also Prooemium demonstrationum anatomicarum in Theatro Hafniensi anni 1673, in Acata Faniensia (1673); Nicolai Stenonis ad novae philosophiae reformatorem de vera philosophia epistola (Florence, 1675); Nicolai Stenonis de propria conversione epistola (Florence, 1677); and Parochourm hoc age seu evidens demonstratio quod parochus teneatur omnes alias occupationes dimittere et suae attendere perfectioni ut commissas sibi oves ad statum salutis aeternae ipsis a Christo praeparatum perducat (Florence, 1684).
II. Secondary Literature. General biographies about Stensen are M. Bierbaum, Niels Stensen. Von der Anatomie zur Theologie (Münster, 1959): R. Cioni, Niels Stensen. Scientist-Bishop (New York, 1962); A. D. Jörgensen, Niels Stensen (Copenhagen, 1958); and G. Scherz. Niels Stensen. Forscher und Denker im Barock (Stuttgart, 1964). More scholarly works on Stensen include G. Scherz, Nicolaus Steno and His Indica (openhagan, 1958), with a biography and various studies of Stensen’s work; and Nicolaus Steno and Brain Research in the Seventeenth Century (London, 1967), from Proceedings of the International Symposium on N. Steno held in Copenhagen, August 1965.
On Stensen’s work in anatomy. see P. Franceschini, “Priorita del Borelli e dello Stenone nella conoscenze dell’ apprarato motore,” in Monitore zollogico italano (1948), and in Rivista di storia della scienze mediche e naturali (1951), 1–15; A. Krogh, “Biologen Niela Stegen. Trehundred År.,” in Nordisk tidsskrift for terapi (1937), 565–578; V. MaaR, “Om Opdagelsen af Ductus Vitello-Intestinalis,” in Kongelige Danske Videnskabernes Selskabs Skrifter (1908), 233–265; M. T. May, “On the Passage of Yolk Into the Intestines of the Chick,” in Journal of the History of Medicine (1950), 119–143; H. P. Philisen “Ductus parotideus Stenonianus,” in Tendlaegetidende, 64 (1960), 221–248; C. Schirren, “Niels Stensen entdeckte vor 300 Jahren die spater nach Fallot beannte Terlogie,” in Mediziniche Welt(1965), 278–280; Th. Schlichting, “Das Tagebuch von Niels Stensen,” in Centaurus (1954), 305–310; C. M. Steenberg, “Niels Stensen som sammenlignende Anatom og Embryolog,” in Naturens Verden (1938), 202–209; and E. Warburg, “Niels Stensen Beskrivelse af det første publicerede Tilfaelde af Fallots Tetradé” in Nordisk medicin, 16 (1942), 3550.
On Stensen’s geological work, see E. Becksmann. “N. Stno (1638–1686) und seine Stellung in der Geschichte der Geologie,” in Zeitschrift der Deutschen geologischen Gesellechaft, 91 (1939), 329–336; A. Garboe, “Niels Stensens (Stenos) geologisk Arbejdes Skaebne,” in Danmarks geologisk undersøgeles, 4 (1948), 1–34; A. Johnsen, “Die Geschichte der kristall-morophologischen Erkenntnis,” in Sitzungsberichte der Presussisshen Akademie der Wissenschaften zu Berlin (1932), 404; Hj. Oedum, “Niels Stensens geologisks Syn og videnskabelige Tankesat,” in Naturens Verden (1938), 49–60; F. Rodolico, “l’evoluzione geologica della Toscana secondo N. Stenone,” in Memorei della Societá toscana di scienze naturali, 60 , ser. A (1953), 3–7; H. Schenk, “Aoolied Paleonotology,” in Bulletin of the American Association of Petroleum Geologists(1940), 1752; G. Scherz, “Niels Stensens Smaragdreise,” in Centaurus (1955), 51–57; and H. Seifart, “Nicolaus Steno als Bahnbrecher der modernen Kristallograpahie,” in Sudhoffs Archiv fur Geshichte der Medizin und der Naturwissenscheaften (1954), 29–47.
The more general works on Stensen and his work are A. Faller, “Die philosophischen Voraussetzungen des Anatomen und Biologen Niels Stensen,” in Arzt and Christ (Salzburg, 1962); K. Larsen, “Stenos Forfold til Filosofi og Religion,” in Kirkehist. Saml. (Copenhagen, 1938), 511–553; J. Nordströam, “Antonio Magliabechi och Nicolaus Steno,” in Lychnos, 20 (1962), 1–42; R. Rome, “Nicolas Stenon (1638–1686). Anatomiste, etc.,” in Revue des questions scientifiques (1956), 517–572; “Nicolas Sténon et la Royal Society,” in Osiris, 17 (1956), 244–268; and G. Scherz, “Danamarks Stensen Manuskript,” in fund og Forskining (Copenhagen, 1958–1959), 19–33; and “Niels Stensen’s First Dissertation,” in Journal of the History of Medicine and Allied Sciences, 15 (1960), 247–264
"Stensen, Niels." Complete Dictionary of Scientific Biography. . Encyclopedia.com. (August 23, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/stensen-niels-0
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"Stensen, Niels." A Dictionary of Earth Sciences. . Encyclopedia.com. (August 23, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/stensen-niels
"Stensen, Niels." A Dictionary of Earth Sciences. . Retrieved August 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/stensen-niels
Niels Stensen: see Steno, Nicolaus.
"Stensen, Niels." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (August 23, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/stensen-niels
"Stensen, Niels." The Columbia Encyclopedia, 6th ed.. . Retrieved August 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/stensen-niels