Galileo Galilei’s confrontation with the Roman Catholic Church famously initiated with the “Letter to Castelli,” penned in December 1613. The correspondence was inspired by a dinner dialogue in Pisa that included Grand Duke Cosimo II de’ Medici, philosopher Cosimo Boscaglia, and Benedetto Castelli. Boscaglia contested the heliocentric theory, referencing Biblical inconsistencies, to which Castelli, a pupil of Galileo, countered. Castelli subsequently communicated the debate he had with the Dowager Duchess Christina to Galileo, which inspired Galileo to write the now-famous letter. In it, Galileo asserted that the Bible should not serve as a reference in scientific debates and offered interpretations of scriptural texts that conformed with the heliocentric perspective.
By proposing ways for the Church to interpret the Bible in relation to scientific issues, Galileo inadvertently trespassed into sensitive ecclesiastical territory during a time rife with Reformation conflicts. The Church, which regarded the Bible as its jurisdiction, viewed this as overreaching. The letter circulated extensively in manuscript form, ultimately drawing the notice of the Inquisition. Galileo later stated that the version possessed by the Inquisition had been altered to implicate him, yet it was subsequently revealed that the text was indeed his original piece.
Benedetto Castelli, beyond being a follower of Galileo, was a distinguished scientist in his own right, making significant contributions to areas such as hydrology and hydraulics. He was born in Brescia in 1578, joined the Benedictine order, and adopted the name Benedetto. He studied under Galileo at the University of Padua and later participated in scientific investigations pertinent to the heliocentric model.
In 1610, Castelli inquired about the phases of Venus with Galileo, resulting in Galileo’s famous confirmation of Venus’s phases, an observation that supported heliocentrism. Although Castelli was involved, Galileo maintained exclusive credit. Castelli’s innovative approach to sunspot observation and his 1615 publication addressing Galileo’s adversaries highlights his scientific prowess.
With Galileo’s support, Castelli was appointed as a mathematics professor at the University of Pisa, where he made further advancements in hydraulics, advising on river dynamics and refining existing Roman engineering literature. In 1628, he released “Delia misura dell’acque Correnti,” marking the beginning of modern hydraulic studies with revelations about fluid dynamics.
After being called to Rome by Pope Urban VIII, Castelli’s expertise broadened, significantly propelling forward Italian hydrology. Furthermore, he guided a diverse array of intellectuals, including Cavalieri, devised new methodologies, and boldly criticized established Venetian hydrological practices—his insights derived from empirical techniques, departing from the conventional Venetian experiential knowledge.
Posthumously, Castelli’s contributions to optics and thermodynamics enhanced his intellectual legacy. His students went on to exert considerable influence in the scientific discussions of the seventeenth century, following his innovative analytical approaches. Castelli’s position as both a groundbreaking thinker and educator profoundly enriched the developing mathematical sciences during this crucial period.