Nicolas Steno

Niels Steensen, known internationally as Nicolas Steno, was born on January 11, 1638, in Copenhagen. Studying medicine in Leiden and Paris, he quickly achieved fame as an anatomist, discovering the parotid duct (Stensen's duct) and demonstrating that the heart is primarily a muscular pump rather than the seat of passions.

Serving as court physician to the Grand Duke of Tuscany in Florence, Steno investigated fossils and sedimentary rock layers in Tuscany. In his 1669 masterpiece De solido intra solidum naturaliter contento dissertationis prodromus, he formulated the law of superposition, the principle of original horizontality, and the law of constant interfacial angles in crystals, establishing geology as an empirical science. He was ordained a Catholic priest in 1675 and beatified by Pope John Paul II in 1988.