Page - 160 - in Maximilian Hell (1720–92) - And the Ends of Jesuit Science in Enlightenment Europe

Chapter 3160 varied from 8.28″ (Planman),64 8.33″ (Stepan Yakovlevich Rumovskii [1734– 1812]),65 8.615″ (Lambert Heinrich Röhl [1724–90]),66 and 8.69″ (James Short [1710–68])67 to 9.00″ (Hell, Lalande),68 9.26″ (Giovanni Battista Audiffredi [1714–94]),69 9.89″ (Thomas Hornsby [1733–1810]),70 and 10.24″ (Pingré).71 Ex- pressed in kilometers, the figures of Planman and Pingré equal 158,884,000 and 128,472,000 kilometers, respectively—twenty percent, a far cry from Halley’s prediction of 0.2, and an unacceptable degree of uncertainty to the contempo- rary “quantifying spirit.”72 Despite the discrepancies between the various attempts to determine the solar parallax, the 1761 transit project was far from being a complete failure. Several features of the phenomenon were investigated, and although some ob- servers missed ingress as well as egress, their observations were still of use for purposes other than the solution of the parallax problem. As Zanotti noted, the transit was useful not only for the definition of the solar parallax: “Also, if we turn to the knowledge of the planet Venus itself, this observation is no doubt to be preferred to any other method that can possibly be attempted in 64 Anders Planman, “A Determination of the Solar Parallax Attempted, by a Peculiar Meth- od, from the Observation of the Last Transit of Venus: By Andrew Planman […] Together with a Letter from Him to Mr. James Short […],” ptrsl 58 (1768; published 1769, paper written in 1767): 127. 65 Stepan Rumovskii, “Investigatio parallaxeos Solis ex observatione transitus Veneris per discum Solis Selenginski habita, collate cum observationibus alibi institutis,” Novi com- mentarii Academiae Scientiarum Imperialis Petropolitanae (hereafter: NcASIP) 11 (1765; published 1767): 487–538, here 510. 66 Lambert Heinrich Röhl, Merkwürdigkeiten von der Durchgängen der Venus durch die Sonne (Greifswald: Röse, 1768), 110. 67 James Short, “Second Paper concerning the Parallax of the Sun Determined from the Late Observations of the Late Transit of Venus […],” ptrsl 53 (1763; published 1764): 340. 68 Hell, Ephemerides 1764 (1763), 225; Lalande, Astronomie, 1st ed. (Paris: Desaint & Saillant, 1764), 800. 69 Audiffredi’s mean value of the solar parallax as calculated in De Solis parallaxi ad V. Cl. Grandjean de Fouchy […] Commentarius (Rome, 1766), was 9.26 seconds, according to Lu- isa Pigatto, “The 1761 Transit of Venus Dispute between Audiffredi and Pingré,” in Kurtz, Proceedings, 74–86, here 83. 70 Thomas Hornsby, “A Discourse of the Parallax of the Sun […],” ptrsl 53 (1763; published 1764): 467–95, here 494; Hornsby’s calculation of “a parallax of the Sun on the day of the transit” of 9.736 seconds represents a mean horizontal parallax of 9.89 seconds; cf. An- dreas Verdun, “Die Bestimmung der Sonnen-Parallaxe aus den Venus-Transits im 18. Jahr- hundert,” Orion 322 (2004/3): 4–20, here 12. 71 Alexandre Guy Pingré, “Nouvelle recherche sur la determination de la parallaxe du Soleil par le passage de Vénus du 6 Juin 1761,” Histoire de l’Académie Royale des Sciences pour l’année 1765 (published 1768): 32. 72 We are indebted to Truls Lynne Hansen (personal communication) for calculating these figures, using the present value of Earth’s equator radius (6,378 kilometers).