Page - 267 - in Maximilian Hell (1720–92) - And the Ends of Jesuit Science in Enlightenment Europe

267Observing Venus and Debating the Parallax observe the eclipse of the Sun, which took place between 9:22 and 11:22 a.m., and would only be visible from the observatoriolum australe.29 As the moment of the transit around midnight, June 3–4, 1769 was ap- proaching, other kinds of preparations were made, too. Of the four contacts of Venus with the limb of the Sun, Hell deemed the first exterior contact impos- sible to observe with anything near the accuracy required. Accordingly, he or- dered his assistants Sajnovics and Borchgrevink to be on the look-out for this event “so as to avoid, by this useless staring at the Sun, to weary and weaken my eye, which I wanted to spare for the precise determination of that utterly im- portant, first interior contact.”30 As soon as the two assistants had exclaimed that they saw “a sort of black thing” (rem quampiam nigram) about to enter the limb of the Sun, Hell placed his eye on the lens of his telescope and estimated, on the basis of the proportion of the disc of Venus that had entered so far, that the real exterior contact had probably taken place some thirty seconds earlier, or 9:14:47 p.m. according to the Viennese clock. Borchgrevink used the ten-foot Dollond, Sajnovics the ten-and-a-half-foot, and Hell the eight-and-a-half-foot telescope for this first observation.31 Before the interior contact at ingress (which took place some seventeen minutes later), Hell and Borchgrevink switched places. Hell now took charge of the Dollond and left the eight-and-a-half-foot telescope for Borchgrevink, whereas Sajnovics continued to use the ten-and-a-half-foot. The statement on the interior contact is divided in two: first, Hell records the moment when the Sun and Venus appeared to the three observers to be perfectly round, then, a moment taking place a few seconds later, when “the shining thread of the Sun’s limb appears” (Apparet filum lucidum limbi Solis). It is the latter of these mo- ments that Hell considers to be the moment of ingressus totalis Veneris (total ingress of Venus), although he concedes that some observers define the former moment as that of “real,” interior contact. The latter moment was seen by Hell at 9:32:48 p.m. according to the Viennese clock, and by Sajnovics three seconds earlier. The amateur observer Borchgrevink in his turn saw it thirty-five sec- onds earlier than Sajnovics.32 Only some seven minutes after total ingress had been observed, clouds started blocking their view to the Sun, and the sky re- mained overcast nearly continuously until less than half an hour before egress 29 Cf. Hell, Observatio transitus Veneris […] 1769, 81. 30 Hell, Observatio transitus Veneris […] 1769, 71–72, here 71. 31 Hell, Observatio transitus Veneris […] 1769, 71. 32 Hell, Observatio transitus Veneris […] 1769, 73.