Today is the memorial of Blessed Nicolas Steno. Niels Steensen was born into a Lutheran family in Copenhagen in 1638. (By the Julian calendar, which Denmark still used, he was born on January 1; by the Gregorian calendar we use today, he was born on January 11.) He had a hard childhood; he was a sickly boy, and thus often had to be isolated, and his father died when he was six. He went into medicine at the University of Copenhagen, and then set off on what can only be considered a lifetime journey, because he spent practically the rest of his life moving from place to place. He became an active researcher in the newly developing subfield of anatomy studying the lymphatic system; another name for the parotid duct is the Stensen duct. While broadly Cartesian himself, he did some of the early work in refuting common Cartesian ideas about the body -- e.g., he contributed to showing that the pineal gland did not have the function that Descartes attributed it and to showing that Harvey was more right than Descartes about the heart. In 1665, he made his way to Florence, where he became the physician to Grand Duke Ferdinando II de'Medici. While there, Steno, dissecting a shark, noted that the teeth were very much like certain kinds of rock formations, glossopetrae. This led him to an extensive investigation of the phenomenon in which we find one kind of rock embedded in another. He also was doing extensive anatomical research on muscles. While he was still engaged in these investigations, he saw a Corpus Christi procession. He had been thinking over his religious views in light of some of the discussions he had had while traveling; discussions with people like Bossuet had led him to conclude that the Lutheran account of the Eucharist was incorrect, and had been reading the Church Fathers, and, watching the eucharistic procession wondered if maybe Catholics were right after all. In 1667, on All Soul's Day, he was received into the Church.
In 1669, he published the Dissertationis prodromus de solido intra solidum naturaliter contento. It is one of the most remarkable and important scientific works of the seventeenth century, and all the more so when one considers that it is only the introduction to a more detailed work that was planned but never completed. It grew out of his thinking about the glossopetrae and the further investigations that this had led him to undertake. The problem Steno posed to himself was a very abstract one, and is that which is given in the title: how to explain the phenomenon of a solid body enclosed by a natural process within a different solid body, which is a specific version of an even more general problem, how, from a given substance produced by natural processes, to determine the place and manner of its production. Steno, of course, quickly saw that solids enclosed within solids would have to be explained by the solids previously being liquid, and then, by considering a wide variety of different examples, proposed his three principles:
(1) "If a solid body is enclosed on all sides by another solid body, of the two bodies that one first became hard which in the mutual contact, expresses on its own surface the properties of the other surface." (We would usually state this principle in the reverse direction, using impression rather than expression.)
(2) "If a solid substance is in every way like another solid substance, not only as regards the conditions of surface, but also as regards the inner arrangement of parts and particles, it will also be like it as regards the manner and place of production, if you except those conditions of place which are found time and again in some place to furnish neither any advantage nor disadvantage to the production of body."
(3) "If a solid body has been produced according to the laws of nature, it has been produced from a fluid."
On the basis of these three principles, you can solve a wide variety of problems. Given the abstract approach, these are of all kinds, but the one that is most significant is that on this basis you can build an accurate account of fossilization, thus setting paleontology on a sure footing. Nor is this all. In the course of the discussions of the Prodromus -- which remember is just Steno laying out the basic summaries of his research as an introduction -- he also establishes basic principles that made it possible to study geological strata and a principle of crystallography that is often seen as one of the foundations of the field, Steno's Law. Perhaps no one else in history has ever managed to advance the geological sciences so much in such a short space.
The full dissertation was perhaps never published because Steno's life underwent a series of disruptions. Ferdinando died in 1670, and, while the Medicis continued to welcome him, for a number of reasons Steno ended up back in Denmark. He had repeatedly tried for professorships, but it had often not worked out, and now he joined the University of Copenhagen as a professor of anatomy. It was not a particularly great time for him. He had previously made a lot of friends in the region, but as it happens, they liked Steno the relaxed secularish Lutheran much more than they liked Steno the earnest Catholic convert. And a Catholic in Copenhagen was a lightning rod for religious controversy; he soon regretted not staying in Florence, so much so that he resigned in 1674 and went back. He was made tutor to the son of Cosimo III, and decided (perhaps due to his recent unpleasant episode in the realm of religious controversy) to do an intensive study of theology. He was ordained in 1675 and the next year was made the titular bishop of Titopolis and appointed Apostolic Vicar of the Nordic Missions by Pope Innocent XI, thus becoming a missionary bishop. It's sometimes said that he did no scientific work after this. This is not strictly true (and is probably due to over-reading a comment by Leibniz, with whom he had had an argument over religious matters); we still see Steno off and on doing scientific work, but as bishop he was an extremely busy man, and none of this scientific research (mostly on the brain) ever quite reached published form. He did publish a number of theological works.
Most of his work, however, was practical; he was active in attempting reform abuses in the Church. He lived a life of voluntary poverty, dressed in a threadbare cloak, living on bread and beer and fasting several days a week. He eventually fell ill, and insisted that his body should be shipped back to Florence, which it was.
From the opening of the Prodromus:
Travellers into unknown realms frequently find, as they hasten on over rough mountain paths toward a summit city, that it seems very near to them when first they descry it, whereas manifold turnings may wear even their hope to weariness. For they behold only the nearest peaks, while the things which are hidden from them by the interposition of those same peaks, whether heights of hills, or depths of valleys, or levels of plains, far and away surpass their guesses; since by flattering themselves they measure the intervening distances by their desire.
So, and not otherwise, is it with those who proceed to true knowledge by way of experiments; for as soon as certain tokens of the unknown truth have become clear to them, they are of a mind that the entire matter shall be straightway disclosed. And they will never be able to form in advance a due estimate of the time which is necessary for loosing that knotted chain of difficulties which, by coming forth one by one, and from concealment, as it were, delay, by the constant interposition of obstacles, them that are hastening toward the end. The beginning of the task merely reveals certain common, and commonly known, difficulties, whereas the matters which are comprised in these difficulties—now untruths which must be overthrown, now truths which must be established; sometimes dark places which must be illumined, and again, unknown facts which must be revealed shall rarely be disclosed by any one before the clew of his search shall lead him thither....
The plaque commemorating him in the Basilica of San Lorenzo:
