(b. Ferrara, Italy, 1598; d. Bologna, Italy, 25 January 1671)
Riccioli entered the Society of Jesus when he was sixteen years old, and there received the comprehensive education that enabled him to teach Italian literature, philosophy, and theology, first at Parma and then at Bologna, while privately pursuing studies in astronomy and geography. He published extensively on the latter topics and these writings made him famous among his contemporaries, even though he rejected Galileo’s example in using the vernacular and wrote most of his works in Latin. His commitment to church doctrine brought him into conflict with the ideas expressed by Galileo and his students and by the Florentine Accademia del Cimento. This attitude, together with the civil and religious pressures inherent in the Counter-Reformation, explains many of the apparent contradictions in Riccioli’s scientific career. Following the Inquisition’s condemnation of Galileo’s astronomical theories, for example, Riccioli became one of the most ardent opponents of the Copernican system, which he tried to refute in every way. He nonetheless recognized the simplicity and the imaginative force of the Copernican theory, and a acknowledged it as the best “mathematical hypothesis”— while striving to divorce it from any effective notion of truth.
In particular Riccioli designed a series of experiments by which he hoped to disprove Galileo’s conclusions, but instead ratified them. This is especially true of his accurate and ingenious investigations of falling bodies. Although he was somewhat hampered by his reluctance to read Galileo’s own works, his won skill as an experimenter served him well. With his fellow Jesuit, Francesco Maria Grimaldi, Riccioli succeeded in perfecting the pendulum as an instrument to measure time, thereby surpassing Galileo and his school and laying the groundwork for a number of important later applications.
Riccioli also made a number of significant astronomical measurements in an effort to expand and refine existing data. To this end he made measurements to determine the radius of the earth and to establish the ratio of water to land. His recourse to a mathematical treatment of these problems is noteworthy. He observed the topography of the moon and, in concert with Grimaldi, introduced some of the nomenclature that is still used to describe lunar features. Riccioli described sunspots, compiled star catalogues, and recorded his observation of a double star; he also noted the colored bands parallel to the equator of Jupiter and made observations of Saturn that, if he had had better instruments, might have led him to recongnize its rings.
As a geographer, Riccioli set out to compose a single great treatise that would embrace all the geographical knowledge of his time. Although he did not complete this task, he published tables of latitude and longitude for a great number of separate localities, in which he corrected previous data and prepared the way for further developments in cartography. Despite the conservation of the age in which he worked, Riccioli made honest and important contributions to science.
I. Original Works. Riccioli’s writings are Geographicae crucis fabrica et usus (Bologna, 1643); Almagestum novum astronomiam veterem novamque complectens (Bologna, 1651, 1653); Theses astronomicae de novissimo comete anni 1652 (Bologna, 1653), an anonymous work attributed to Riccioli by Lalande; Geographiae et hydrographiae reformatae (Bologna, 1661; Venice, 1672); Astronomiae reformatae, 2 vols. (Bologna, 1665); Vindiciae kalendarii Gregoriani adversus Franciscum Leveram (Bologna, 1666), published under the name of Michele Manfredi; Argomento fisico-mattematico… contro il moto diurno della terra (Bologna, 1668); Apologia proargumento physico-mathematico contra systema Copernicanum (Venice, 1669); and Chronologiae reformatae et ad certas conclusiones redactae, 3 vols. (Bologna, 1669).
II. Secondary Literature. An annotated bibliographic survey of Riccioli’s writings is given in P. Riccardi, Biblioteca matematica italiana, I (Modena, 1893), cols. 370–374; Riccardi does not consider De semidiametro terrae (Bologna, 1655), sometimes attributed to Riccioli, to be by him. Sources on Riccioli cited by Riccardi include P. Alegambe, Bibliotheca scriptorum Soc. Jesu post exclusum (Antwerp, 1643), 416; A. de Backer, Bibliothèque des écrivains de la compagnie de Jésus (Liège, 1853–1861); J. S. Bailly, Histoire de l’astronomie moderne, II (Paris, 1779), 216; G. A. Barotti, Memorie istoriche de’ letterati ferraresi, II (Ferrara, 1793), 270; Jacques Cassini, De la grandeur et de la figure de la terre, II (Paris, 1720 ); G. B. Corniani, I secoli della letteratura italiana commentario, 9 vols. (Brescia, 1818–1819); A. Fabroni, Vitae italorum doctrina excellentium, 20 vols. (Pisa, 1778–1805); A. Libes, Histoire philosophique des progrès de la physique, 4 vols. (Paris, 1810–1813); J. E. Montucla, Historie des mathématiques, 2nd ed., 4 vols. (Paris, 1799–1802); G. Tiraboschi, Storia della letteratura italiana, 27 vols. (Venice, 1822–1825); and Luigi Ughi, Dizionario storico degli uomini illustri ferraresi, II (Ferrara, 1804), 93.