Page - 287 - in Maximilian Hell (1720–92) - And the Ends of Jesuit Science in Enlightenment Europe

287Observing Venus and Debating the Parallax preliminary calculations would be followed by new tentative adjustments and so forth. Hell chose the former, Lalande the latter strategy. Lalande had pub- lished parallaxes of 9″ (Gazette de France [January 1770]) or 9.18″ (Journal des Sçavans [April 1770]) before he had access to the observation of Hell. Having received the Vardø observation as well as Chappe’s from California, he adjusted it to approximately 8.75″ (Gazette de France [December 1770]) or 8.80″ (Journal des Sçavans [May 1771]) or again 8.75″ (second edition of the Astronomie [ August 1771]), until he upon the arrival of the Tahiti observation changed it yet again, to 8.50″ (Gazette de France [September 1771]; Journal des Sçavans [ December 1771]). From then on, he stayed fixed on 8.50″, or 8.60″ as a maxi- mum (third edition of the Astronomie [1792]). If we look behind these numbers and pay attention to how Lalande arrived at the results, we find that he—although dismayed at its late arrival—initially held no prejudices against the Vardø observation. Quite the contrary: in a letter to Boscovich, dated December 15, 1771, he put together a table in which the observations of Cajaneborg and Vardø are compared with those of Hudson Bay, California, and Tahiti, adding that the largest difference between the three results yielded by comparisons with Cajaneborg is 0.5 arc seconds, whereas with Vardøhus it is only 0.3″. This makes it probable that the Vardøhusian observation is more exact than the former. Thus, if we were to take the mean between the three comparisons, staying closer to the observation of Vardøhus than that of Cajaneborg in a 5:3 relation and then taking the mean between the three last results, we get [a solar parallax of] 8.6″ rather than 8.5″.88 Simultaneously, Hell arrived at his conclusion of 8.70″, which he based primar- ily upon his own observation from Vardø and that of Green from Tahiti. The observers in Tahiti varied several seconds between each other in their determi- nations of the moments of contact, but Hell stuck to the observation of the professional astronomer Green, skipping those of Admiral Cook and natural historian Daniel Solander (1733–82). The same applied for the Vardø observa- tion, where the inexperienced Borchgrevink diverged substantially from Hell and Sajnovics. Trusting the professional and most experienced observers, Hell rejected all other observations and tried to persuade his colleagues that the 88 Lalande to Boscovich, dated Paris, December 15, 1772, cited in Vladimir Varićak, “Drugi ulomak Boškovićeve korespondencije,” Rad Jugoslavenske akademije znanosti i umjetnosti, Matematičko-prirodoslovni razred 52 (1912): ccclxviii–ccclxx.