December 31

Serving the Holy Roman Empire, Belli combined military experience with legal scholarship to address the conduct of warfare. His 1563 work 'De re militari et jure bellico' analyzed the rights and duties of soldiers, prisoners, and civilians in conflict, influencing later developments in international humanitarian law. Belli's writings blended Roman legal principles with practical insights from battlefields across Europe. He held high office in Piedmont, advising dukes on military organization and justice. Recognized as a pioneer in military jurisprudence, his theories remained authoritative for centuries within European legal traditions.

Thomas Erastus (1524–1583) was a Swiss physician and theologian best known for his theory of Erastianism, which argued that the state should have supremacy in ecclesiastical discipline. He studied medicine and theology at prominent European universities and served as city physician in Basel. Erastus authored influential treatises on medical practice and ecclesiology, engaging in debates during the Swiss Reformation. His ideas sparked controversy and shaped discussions on the relationship between church and state for centuries. Though his name became synonymous with Erastianism, he also contributed significantly to early medical knowledge.

Ludolph van Ceulen (1540–1610) was a pioneering mathematician who dedicated much of his career to approximating the value of π using polygonal methods. In his work De Circuli Dimensione, he recorded π to 35 decimal places, a record that stood for many years. Van Ceulen held a professorship at Leiden University, where he taught mathematics and astronomy. His efforts led to the term “Ludolphine number” in several European languages in honor of his achievement. He influenced future generations of mathematicians with his rigorous computational techniques and methodology.

Giovanni Alfonso Borelli (1608–1679) applied principles of mechanics to biological systems, pioneering the field of biophysics. His landmark work De Motu Animalium analyzed muscular motion, blood circulation, and animal locomotion through mathematical models. Borelli was a member of the Accademia del Cimento in Florence and contributed to studies in astronomy and hydrodynamics. His rigorous analytical methods influenced later scientists such as Newton and Euler. Borelli’s interdisciplinary approach laid the groundwork for quantitative physiology.

Robert Boyle (1627–1691) was an influential natural philosopher and a founding member of the Royal Society. His work The Sceptical Chymist challenged the traditional alchemical view of matter and established the importance of experimental methods in chemistry. Boyle’s law, describing the inverse relationship between the pressure and volume of a gas, became a cornerstone of physical chemistry. He also developed early vacuum pumps and conducted groundbreaking experiments on air and its properties. Boyle’s commitment to empirical research helped lay the foundations for modern scientific inquiry.

Dudley North (1641–1691) was a prominent London merchant who served as a director of the Levant Company and traded extensively with the Ottoman Empire. His work A Discourse upon Trade argued for free trade principles and market competition, influencing early modern economic thought. North’s detailed diaries offer historians valuable perspectives on commercial practices, prices, and daily life in Restoration England. As an economist and businessman, he combined practical trading experience with theoretical analysis. North’s contributions laid groundwork for later classical economists and economic liberalism.

John Flamsteed (1646–1719) was an English astronomer appointed as the first Astronomer Royal in 1675, tasked with charting the heavens to aid navigation. Over his lifetime, he compiled the 'Historia Coelestis Britannica,' a meticulous star catalogue and atlas that significantly improved celestial navigation and mapping. Flamsteed's dedication to precise observational methods set new standards in astronomy, influencing generations of astronomers. He installed state-of-the-art instruments at the Royal Observatory in Greenwich and observed over 3,000 stars. Despite conflicts with contemporaries like Sir Isaac Newton, his work endured and laid foundations for modern positional astronomy. His star data remained the definitive reference for decades after his death.

Born in 1808, Hirsch emerged as a leading rabbinic figure in 19th-century Germany. He championed "Torah im Derech Eretz," advocating the compatibility of Jewish law with secular knowledge. As a prolific writer, he published influential commentaries on the Pentateuch and sermons for contemporary audiences. Hirsch founded Jewish educational institutions and led the Jewish community in Frankfurt am Main. His ideas shaped Orthodox Jewish thought worldwide, emphasizing intellectual engagement and community organization. He remained active until his death in 1888, leaving a lasting legacy on modern Orthodoxy.

Born around 1809, Crowther was captured into slavery but later freed and educated by the Church Missionary Society. Ordained in England, he returned to West Africa to establish missionary stations. In 1864, he became the first African bishop of the Niger Diocese. A gifted linguist, Crowther compiled grammars and dictionaries for Yoruba and other languages, enabling literacy and local translations. His work fostered indigenous leadership in the church. Crowther died in 1891, leaving a profound impact on African Christianity and linguistic scholarship.

Born in 1856, Stieltjes studied law before dedicating himself to mathematics. His work on continued fractions and orthogonal polynomials led to the definition of the Stieltjes integral, a key concept in analysis. He served as a professor at the University of Delft and mentored future Dutch mathematicians. Stieltjes also contributed to number theory and the theory of moments, influencing probability and functional analysis. He passed away in 1894, and his innovations remain fundamental in modern mathematical research.

Born in 1849 in Massachusetts, Cornelia Clapp graduated from Mount Holyoke College and studied under Louis Agassiz at Harvard. In 1879 she began work at the Marine Biological Laboratory (MBL) in Woods Hole, focusing on bryozoans and other marine invertebrates. She became the first woman on the MBL faculty in 1892 and later served as director of its zoology department. A dedicated educator, she taught zoology and mentored countless students, advocating for women's participation in science. Clapp's publications and leadership helped establish marine biology as a rigorous scientific discipline in the United States. Her pioneering spirit and scholarly contributions left a lasting legacy in the field of marine zoology.

Born in 1928, Vasily Lazarev graduated as a physician before joining the Soviet Air Force and rising to the rank of colonel. Selected as a cosmonaut in the 1960s, he flew on missions to the Salyut space stations during the 1970s. During his time in orbit, he conducted biomedical experiments to study the effects of microgravity on the human body. Lazarev logged over ten days in space, helping to pave the way for longer-duration missions. After retiring from active flight duty, he contributed to cosmonaut training and space medicine research. He died on December 31, 1990, remembered for his pioneering role in human space exploration.