Giovanni Battista Riccioli
Giovanni Battista Riccioli was an Italian astronomer and a Catholic priest in the Jesuit order. He is known, among other things, for his experiments with pendulums and with falling bodies, for his discussion of 126 arguments concerning the motion of the Earth, and for introducing the current scheme of lunar nomenclature. He is also widely known for discovering the first double star. He argued that the rotation of the Earth should reveal itself because on a rotating Earth, the ground moves at different speeds at different times.
The asteroid 122632 Riccioli is named after him.
Biography
Riccioli was born in Ferrara. He entered the Society of Jesus on 6 October 1614. After completing his novitiate, he began to study humanities in 1616, pursuing those studies first at Ferrara, and then at Piacenza.From 1620 to 1628 he studied philosophy and theology at the College of Parma. Parma Jesuits had developed a strong program of experimentation, such as with falling bodies. One of the most famous Italian Jesuits of the time, Giuseppe Biancani, was teaching at Parma when Riccioli arrived there. Biancani accepted new astronomical ideas, such as the existence of lunar mountains and the fluid nature of the heavens, and collaborated with the Jesuit astronomer Christoph Scheiner on sunspot observations. Riccioli mentions him with gratitude and admiration.
By 1628 Riccioli's studies were complete and he was ordained. He requested missionary work, but that request was turned down. Instead, he was assigned to teach at Parma. There he taught logic, physics, and metaphysics from 1629 to 1632, and engaged in some experiments with falling bodies and pendulums. In 1632 he became a member of a group charged with the formation of younger Jesuits, among whom Daniello Bartoli. He spent the 1633–1634 academic year in Mantua, where he collaborated with Niccolò Cabeo in further pendulum studies. In 1635 he was back at Parma, where he taught theology and also carried out his first important observation of the Moon. In 1636 he was sent to Bologna to serve as Professor of theology.
Riccioli described himself as a theologian, but one with a strong and ongoing interest in astronomy since his student days, when he studied under Biancani. He said that many Jesuits were theologians, but few were astronomers. He said that once the enthusiasm for astronomy arose within him he could never extinguish it, and so he became more committed to astronomy than theology. Eventually his superiors in the Jesuit order officially assigned him to the task of astronomical research. However, he also continued to write on theology.
Riccioli built an astronomical observatory in Bologna at the College of St. Lucia, equipped with many instruments for astronomical observations, including telescopes, quadrants, sextants, and other traditional instruments. Riccioli dealt not only with astronomy in his research, but also with physics, arithmetic, geometry, optics, gnomonics, geography, and chronology. He collaborated with others in his work, including other Jesuits, most notably Francesco Maria Grimaldi at Bologna, and he kept up a voluminous correspondence with others who shared his interests, including Hevelius, Huygens, Cassini, and Kircher.
He was awarded a prize by Louis XIV in recognition of his activities and their relevance to contemporary culture.
Riccioli continued to publish on both astronomy and theology up to his death. He died in Bologna at 73 years of age.
Scientific work
''Almagestum Novum''
One of Riccioli's most significant works was his 1651 Almagestum Novum, an encyclopedic work consisting of over 1500 folio pages densely packed with text, tables, and illustrations. It became a standard technical reference book for astronomers all over Europe: John Flamsteed, the first English astronomer royal, a Copernican and a Protestant, used it for his Gresham lectures; Jérôme Lalande of the Paris Observatory cited it extensively even though it was an old book at that point; the 1912 Catholic Encyclopedia calls it the most important literary work of the Jesuits during the seventeenth century. Within its two volumes were ten "books" covering every subject within astronomy and related to astronomy at the time:- the celestial sphere and subjects such as celestial motions, the equator, ecliptic, zodiac, etc.
- the Earth and its size, gravity and pendulum motion, etc.
- the Sun, its size and distance, its motion, observations involving it, etc.
- the Moon, its phases, its size and distance, etc.
- lunar and solar eclipses
- the fixed stars
- the planets and their motions, etc. ;
- comets and novae
- the structure of the universe—the heliocentric and geocentric theories, etc.
- calculations related to astronomy.
Pendulums and falling bodies
Riccioli is credited with being the first person to precisely measure the acceleration due to gravity of falling bodies. Books 2 and 9 of the New Almagest Riccioli included a significant discussion of and extensive experimental reports on the motions of falling bodies and pendulums.He was interested in the pendulum as a device for precisely measuring time. By counting the number of pendulum swings that elapsed between transits of certain stars, Riccioli was able to experimentally verify that the period of a pendulum swinging with small amplitude is constant to within two swings out of 3212. He also reported that a pendulum's period increases if the amplitude of its swing is increased to 40 degrees. He sought to develop a pendulum whose period was precisely one second – such a pendulum would complete 86,400 swings in a 24-hour period. This he directly tested, twice, by using stars to mark time and recruiting a team of nine fellow Jesuits to count swings and maintain the amplitude of swing for 24 hours. The results were pendulums with periods within 1.85%, and then 0.69%, of the desired value; and Riccioli even sought to improve on the latter value. The seconds pendulum was then used as a standard for calibrating pendulums with different periods. Riccioli said that for measuring time a pendulum was not a perfectly reliable tool, but in comparison with other methods it was an exceedingly reliable tool.
With pendulums to keep time and a tall structure in the form of Bologna's Torre de Asinelli from which to drop objects, Riccioli was able to engage in precise experiments with falling bodies. He verified that falling bodies followed Galileo's "odd-number" rule so that the distance travelled by a falling body increases in proportion to the square of the time of fall, indicative of constant acceleration. According to Riccioli, a falling body released from rest travels 15 Roman feet in one second, 60 feet in two seconds, 135 feet in three seconds, etc. Other Jesuits such as the above-mentioned Cabeo had argued that this rule had not been rigorously demonstrated. His results showed that, while falling bodies generally showed constant acceleration, there were differences determined by weight and size and density. Riccioli said that if two heavy objects of differing weight are dropped simultaneously from the same height, the heavier one descends more quickly so long as it is of equal or greater density; if both objects are of equal weight the denser one descends more quickly.
For example, in dropping balls of wood and lead that both weighed 2.5 ounces, Riccioli found that upon the leaden ball having traversed 280 Roman feet the wooden ball had traversed only 240 feet. He attributed such differences to the air, and noted that air density had to be considered when dealing with falling bodies. He illustrated the reliability of his experiments by providing detailed descriptions of how they were carried out, so that anyone could reproduce them, complete with diagrams of the Torre de Asinelli that showed heights, drop locations, etc.
Riccioli noted that while these differences did contradict Galileo's claim that balls of differing weight would fall at the same rate, it was possible Galileo observed the fall of bodies made of the same material but of differing sizes, for in that case the difference in fall time between the two balls is much smaller than if the balls are of same size but differing materials, or of the same weight but differing sizes, etc., and that difference is not apparent unless the balls are released from a very great height. At the time, various people had expressed concern with Galileo's ideas about falling bodies, arguing that it would be impossible to discern the small differences in time and distance needed to adequately test Galileo's ideas, or reporting that experiments had not agreed with Galileo's predictions, or complaining that suitably tall buildings with clear paths of fall were not available to thoroughly test Galileo's ideas. By contrast, Riccioli was able to show that he had carried out repeated, consistent, precise experiments in an ideal location. Thus as D. B. Meli notes,
Riccioli's accurate experiments were widely known during the second half of the century and helped forge a consensus on the empirical adequacy of some aspects of Galileo's work, especially the odd-number rule and the notion that heavy bodies fall with similar accelerations and speed is not proportional to weight. His limited agreement with Galileo was significant, coming as it did from an unsympathetic reader who had gone so far as to include the text of Galileo's condemnation in his own publications.