Astronomical Images : Motion experiments (Tower of Asinella)

Giovanni Battista Riccioli

Astronomical Images

This image and excerpt are found in the section of Giovanni Battista Riccioli's Almagestum novum (1651) that addressed the question of the world systems. Educated at Jesuit schools in Ferrara, Piacenza, and Parma, Riccioli began teaching at the Jesuit College in Parma in 1632. His career also took him to Mantua and Bologna, where, like most Jesuit professors of his day, he taught a wide variety of subjects, including logic, natural philosophy, mathematics, and theology. Riccioli's publications were equally diverse and included not only astronomical texts, such as his Almagestum novum and Astronomia reformata (1665), but also his Geographia et hydrographia (1661) and various theological treatises. The Jesuit community at Parma and Bologna, where Riccioli studied and taught, was known for its commitment to experimental and observational methods and its interest in the newest developments in astronomy and natural philosophy. Riccioli quickly became immersed in this culture. As a student, Riccioli first learned from and assisted the work of more established professors, including the well-known Jesuit mathematician Giuseppe Biancani (1566-1624). Riccioli almost certainly assisted Biancani and Christoph Scheiner in the latter's observation of sunspots and in the debates over Aristotelian cosmology that followed. Later, as an established professor and scholar, Riccioli directed his students and colleagues in a programme of experimental work. Partly in collaboration with Niccolo Cabeo (1586-1650), a Jesuit from Ferrara who carried out experiments to challenge Galileo's findings on local motion, Riccioli devised an ambitious experimental programme to investigate free fall, the trajectories of projectiles, and the behaviour of pendulums; all topics treated at length in Galileo's Discorsi. This experimental work, along with astronomical observations made at the newly-constructed Jesuit observatory at Santa Lucia College in Bologna, comprised much of the preparatory work for Riccioli's Almagestum novum, which he began in 1640. Though Riccioli intended his Almagestum novum to comprise three volumes, only the first was printed. Riccioli devoted an entire section of the second tome to the Copernican doctrine. He ultimately concluded that arguments drawn from physical and observational evidence were insufficient to determine which world system was correct. After analysing forty-nine proofs for and seventy-seven proofs against the Copernican doctrine, Riccioli sided against the Copernican hypothesis on the basis of the Church's 1616 and 1633 decisions on this matter. In this section of his text, Riccioli described experiments he carried out at the Tower of Asinelli to verify Galileo's findings on free fall. He worked with collaborators to drop objects of differing weights from tall buildings and timed their falls. Through these experiments, Riccioli verified Galileo's so-called 'odd-numbered rule', namely that the distances through which naturally accelerated objects travel in a given unit of time are proportional to the odd numbers. That is, the distances travelled by naturally accelerating objects are proportional to the squares of the times.