STENSEN, NIELS, also known as Nicolaus Steno (b. Copenhagen, Denmark, 1%6111 January 1638; d. Schwerin, Germany, 25 November/5 December 1686), anatomy, geology, mineralogy.

    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 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.

BIBLIOGRAPHY

I. ORIGINAL 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 anatomica de glandulis 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%611667), also published as Bibliotheca anatomica (London, 1709 - 1714), an abridged English version; Discours . . . sur l'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[ldenburg], 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 Parochorum 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