Seite - 155 - in Maximilian Hell (1720–92) - And the Ends of Jesuit Science in Enlightenment Europe

155The 1761 Transit of Venus and Hell’s Transition to Fame 1761 and 1762, made in Vienna and elsewhere).52 In this addition to the Venus transit coverage in the Ephemerides, we find observations from Tranquebar and the Cape of Good Hope along with the observations of the two most fa- mous French expeditionists of 1761, Pingré on the Isle of Rodrigues (taken from a letter by Messier) and Chappe d’Auteroche in Tobolsk (taken from a printed report as well as a letter “benevolently communicated to me by that author”).53 Finally, with the publication of a calculation of the solar parallax based on virtually the entire range of the 1761 Venus transit observations by Anders Plan- man, an astronomer and professor of physics at the University of Åbo (Turku), the full harvest of the global enterprise eventually found its way to print in Hell’s Ephemerides. Grateful users of the annual could hardly have avoided the conclusion that access to all this stock of knowledge was largely thanks to the  spider in the web: Hell, in whom the faithful Jesuit, the loyal servant of the Austrian dynasty and government, and the diligent, competent, and useful member of the “republic of astronomy” were inextricably intertwined as build- ing blocks of a carefully constructed public persona. 3 Lessons Learned The main interest of contemporary astronomers, as stressed by Zanotti in the quote at the beginning of this chapter, was to calculate the size of the solar parallax. For the attainment of this goal, it was vital to have as many reliable observations from sites ranging as far apart as possible. Logistical and political obstacles aside, it ought to have been a straightforward process. However, not only the weather but also a range of technical and optical challenges compli- cated the project and made a seamless calculation of the solar parallax impos- sible. As a broad generalization, there turned out to be at least three sources of error involved in the delicate process of observing a Venus transit. First, regardless of whether the method of Halley or that of Delisle was cho- sen, exact time-keeping was a crucial factor. John Harrison (1693–1776) invent- ed the chronometer just on the eve of the transits of Venus. However, only prototypes of the technology were at hand, and these were widely held to be insufficiently tested for scientific use.54 Thus, pendulum clocks were the only 52 Hell, Ephemerides 1764 (1763), 208–25. 53 Hell, Ephemerides 1764 (1763), 221. 54 Cf., e.g., Jim Bennett, “The Travels and Trials of Mr Harrison’s Timekeeper,” in Instruments, Travel, and Science: Itineraries of Precision from the Seventeenth to the Twentieth Century, ed. Marie-Noëlle Bourguet, Christian Licoppe, and H. Otto Sibum (London: Routledge, 2002), 75–95.