Giovanni Battista Riccioli

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Giovanni Battista Riccioli : biography

17 April 1598 – 25 June 1671

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 (a table in the New Almagest contains data on twenty one such paired drops). He attributed such differences to the air, and noted that air density had to be considered when dealing with falling bodies.Meli 2006 (pp. 132-134); Koyré 1955 (p. 352). He illustrated the reliability of his experiments by providing detailed descriptions of how they were carried out, so that anyone could reproduce them,Meli 2006 (p. 132). Riccioli’s results are generally consistent with a modern understanding of bodies falling under the influence of gravity and air drag. His 15-60-135 values imply a gravitational acceleration "g" of 30 Roman feet per second per second (30 Rmft/s/s). The modern accepted value (g = 9.8 m/s/s) expressed in Roman feet is g = 33 Rmft/s/s; Riccioli’s "g" differs from the accepted value by less than 10%. His statements about balls that are more dense, etc. reaching the ground first (that is, being less affected by air drag) agree with modern understanding. His result that a wooden ball fell 240 feet in the time a lead ball of the same weight fell 280 feet is generally consistent with modern understanding (although the 40 ft difference is somewhat less than expected). complete with diagrams of the Torre de Asinelli that showed heights, drop locations, etc.Raphael 2011 (82-86).

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.Koyré 1955 (p. 352). 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.Raphael 2011 (pp. 82-86). Thus as D. B. Meli notes,

Riccioli’s accurate experiments were widely known during the second half of the [seventeenth] 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.Meli 2006 (p. 134).

Working Concerning the Moon

Riccioli and Grimaldi extensively studied the moon, of which Grimaldi drew maps. This material was included in Book 4 of the New Almagest.Riccioli 1651, . Grimaldi’s maps were based on earlier work by Johannes Hevelius and Michael Van Langren. On one of these maps, Riccioli provided names for lunar features—names which are the basis for the nomenclature of lunar features still in use today. For example, Mare Tranquillitatis (The Sea of Tranquility, site of the Apollo 11 landing in 1969), received its name from Riccioli. Riccioli named large lunar areas for weather. He named craters for significant astronomers, grouping them by philosophies and time periods.Bolt 2007 (pp. 60-61). Although Riccioli rejected the Copernican theory, he named a prominent lunar crater "Copernicus", and he named other important craters after other proponents of the Copernican theory such as Kepler, Galileo and Lansbergius. Because craters that he and Grimaldi named after themselves are in the same general vicinity as these, while craters named for some other Jesuit astronomers are in a different part of the Moon, near the very prominent crater named for Tycho Brahe, Riccioli’s lunar nomenclature has at times been considered to be a tacit expression of sympathy for a Copernican theory that, as a Jesuit, he could not publicly support.Whitaker 1999 (p. 65). However, Riccioli said he put the Copernicans all in stormy waters (the Oceanus Procellarum).Bolt 2007 (p. 61). Another noteworthy feature of the map is that Riccioli included on it a direct statement that the moon is not inhabited. This ran counter to speculations about an inhabited moon that had been present in the works of Nicholas of Cusa, Giordano Bruno, and even Kepler, and which would continue on in works of later writers such as Bernard de Fontenelle and William Herschel.Crowe 2008 (pp. 2, 550).