ON DEDUCING THE UNOBSERVABLE: NICOLAUS STENO'S SEMINAL ILLUSTRATIONS IN EARTH SCIENCE AND BIOLOGY TELL ABOUT A METHOD TO DESCRIBE CONCEALED MECHANISMS AND SOLID TRANSFORMATIONS

Past events are in principle unobservable except for reconstructions from remaining solid traces. It will be shown that the Danish anatomist and pioneer in Earth science Niels Stensen, also known as Nicolaus Steno, in scientific treatises from 1661 to 1673 made deductions from observations to propose hypotheses on concealed mechanisms and structural transformations and thus challenged myths based on a formative faculty of rocks producing fossils, e.g. see Table. Likewise in biology he challenged myths on concealed mechanisms based on inherent qualities like that of animal spirits effecting movements of muscles and the heart. His seminal illustrations were drawn from direct observations but in some examples, processes concealed from direct observation were depicted in two or more consecutive illustrations. His strategies to obtain certainty on concealed processes will be described. With cumulated evidence his deductions became basic theories if not just common knowledge. Methods used by Steno to study concealed processes are still valid.

TABLE. EXEMPLARS OF CASES STUDIED BY STENO

	Objects studied	Concepts challenged	Events and mechanisms deduced	Page*
1	Teeth of shark and glossopetrae	A formative ability of rocks	Biological origin of fossils	574-575
2	Stratified rocks	Landscapes created as they are seen	Stratified rocks are deposits in a sea earlier covering the area; layers indicate a chronology	658
3	Crystals of different size	Crystals grow from the inside	Growth of crystals from the surface by accretion with constant inter-facial angles	658
4	Secretory ducts of glands	Glands are sponges removing excess liquid	Saliva and filtered from arterial blood in glands	372, 412
5	The heart dissected	Passions of the soul heat the heart	The heart is only a muscle	464
6	Pennate muscle structure	Expansion by animal spirits causes muscle contraction	Fiber shortening and muscle structure enable contraction without change of volume	553

* Kardel T, Maquet P, eds. Nicolaus Steno, Springer, Heidelberg 2013.