Seite - 135 - in Maximilian Hell (1720–92) - And the Ends of Jesuit Science in Enlightenment Europe

135The 1761 Transit of Venus and Hell’s Transition to Fame 1769 attracted massive public interest, as well as lavish funding from European governments for expeditions into remote regions of the world. The principal scientific reason was that the transits of Venus were seen as unique opportuni- ties to calculate the distance between the Earth and the Sun, a coveted feat in the “quantifying spirit” of the Enlightenment. Early on in the seventeenth cen- tury, Kepler’s groundbreaking work on the orbits of the planets had laid the foundations for calculations that enabled sky-watchers to be prepared for spectacular events, such as transits of Venus. The Newtonian theory of gravita- tion and mechanics further improved the methods for calculating the move- ments of the planets, but there were still considerable uncertainties about the actual distances between the Sun and the various planets. A transit of Venus was seen as the best way to solve the problem. As pointed out by Edmond Hal- ley (1656–1742), who forecasted the 1761 and 1769 transits,3 observations of Ve- nus in front of the Sun from widely separated sites on the Earth would reveal tiny shifts from which the absolute distance between the Sun and the Earth could be deduced. Once the Sun–Earth distance was known, the distances be- tween all the other planets in the solar system could be inferred as well, by means of Kepler’s Third Law.4 The stakes were thus nothing less than the very dimensions of the solar system and the place of the Earth within it. Excitement among contempo- raries  ran high, and no less considerable is the interest paid by modern schol- ars to  what has been recognized as the greatest collaborative effort in eighteenth-century field science.5 Indeed, already in 1761, at least 130 successful 3 Edmond Halley, “Methodus singularis quâ Solis parallaxis sive distantia à Terra, ope Veneris intra Solem conspiciendæ, tuto determinari poterit,” ptrsl 29 (1714/16; printed 1717): 454–64. This was an elaboration of a paper read before the Royal Society in 1691, itself based on ideas conceived during Halley’s observation of a transit of Mercury at the island of St. Helena in 1677. 4 Kepler had found that “the squares of the times of revolution (periods) of the planets are proportional to the cubes of their mean distances from the sun” (quoted after Woolf, The Transits of Venus, 3). Whereas the times spent by each of the then known planets—Mercury, Venus, Earth, Mars, Jupiter, and Saturn—in encircling the Sun were known to Kepler, he could only guess at the distances between them. However, as soon as the distance between the Sun and any of the planets in the solar system was known, the size of the whole system could be deduced by means of this Third Law. For a discussion of the mathematical princi- ples behind the Third Law, see A.E.L. Davis, “Kepler’s Angular Measure of Uniformity: How It Provided a Potential Proof of His Third Law,” in Miscellanea Kepleriana: Festschrift für Volker Bialas, ed. Friederike Boockmann, Daniel A. Di Liscia, and Hella Kothmann (Augsburg: Erwin Rauner Verlag, 2005), 157–73. 5 Historical accounts of past transits of Venus, with ample explanations as to how they were predicted, how they were used for computation of the solar parallax, how they were observed,