Page - 163 - in Maximilian Hell (1720–92) - And the Ends of Jesuit Science in Enlightenment Europe

163The 1761 Transit of Venus and Hell’s Transition to Fame object as a moon of Venus would be a minuscule spot somewhere on the disc of the Sun just before, during, or after the transit. In the 1760 preparatory man- ual, Hell had in fact reminded observers that finally, both on the day preceding the transit, and on the day of the transit itself, the disc of the Sun should be investigated frequently, to see wheth- er perhaps some smaller, perfectly round spot is there to be seen on the disc of the Sun, a spot moving either in the same or the opposite direc- tion as Venus, but at a speed either exceeding, or at least equaling— certainly not trailing behind—that of Venus. Such a spot, moving in such a way, should represent the moon of Venus, which various observers be- lieve they have seen long ago, under other circumstances.82 Many did look for it, but no one reported having seen such a thing.83 Hell also remained silent about the possible existence (or non-existence) of this moon in his report of 1761. In 1765, however, a refutation of all “observations” of the moon of Venus as nothing more than optical illusions was issued in Vienna with the title “On the Moon of Venus” (De satellite Veneris). The author of this rather sensational publication was none other than Maximilian Hell. There were two factors that had led him to publish this work, he explained. One was that a few years earlier he had presented his thoughts on the non-existence of the “Venus moon” in a letter to Lacaille, his formal contact at the Académie des Sciences in Paris. After Lacaille’s death in 1762, this letter was transferred to the hands of others, and Hell felt embarrassed that the preliminary thoughts he had intended to ventilate to Lacaille alone were now being discussed by several savants in France. The other stimulus was that, in 1764, another set of “observations” of the “Venus moon”—this time from Copenhagen—was published, and since die Sonnenscheibe,” Neues Hamburgisches Magazin 6, no. 37 (1769): 114–56, esp. 119, and Marlot, Les passages de Vénus, 101–4. Baudouin’s memoir—remarkably, given its date—is referred to by Hell in a letter to Lalande dated Vienna, June 12, 1761. It is also mentioned in his printed report on the transit (“Observatio transitus Veneris […] 1761,” 38). Neither of these references is accompanied by any criticism on Hell’s part. 82 Hell, Transitus Veneris, 10. 83 See, e.g., Fer[r]ner, “An Account of the Observations on the Same Transit Made in and near Paris […],” ptrsl 52, no. 1 (1761; published 1762): 225; or Wargentin’s assessment of the results of the Swedish Venus transit observations, “Anmärkningar öfver Planeten Ven- eris gång genom Solens Discus,” kvah 23 (July–September 1761): 179. For further refer- ences, see Kragh, Moon That Wasn’t.