Page - 265 - in Maximilian Hell (1720–92) - And the Ends of Jesuit Science in Enlightenment Europe

265Observing Venus and Debating the Parallax Hell’s manuscript “Astronomical and Other Observations Made during the Scientific Journey from Vienna to Vardø” (hereafter referred to as his “astro- nomical notebook”) gives additional information.24 Here, Hell records even more observations of the Sun than those that are found in Sajnovics’s diary, and what is more, the observations are accompanied with calculations and sometimes even theoretical deliberations. The conspicuous difference be- tween the preliminary results of November 1768 and the final conclusions in the printed report—from around 70° 20′ or even 70° 19′ 30″, to 70° 22′ 36″—is explained by the error of the quadrant, which had not yet been determined in the autumn.25 Thus, when Hell in his notebook on October 16–18, 1768 records observations giving pole heights ranging from 70° 20′ 26″ to 70° 21′ 12″, ending with a mean value of 70° 20′ 25″ (sic), he has added in a slightly different ink, +1 30 error Quadr., and concluded that the pole height should be 70° 22′ 55″. Of course, 70° 20′ 25″ plus 1′ 30″ does not give 70° 22′ 55″, but 70° 21′ 55″. Neither figure, however, is too far from that of 70° 22′ 36″, which ultimately appeared in the Venus transit report. The difference between the 70° 20′ 25″ in the astro- nomical notebook of October 1768 and the approximate value of 70° 19′ 30″ or 70° 20′ in the letters of November and January suggests that Hell initially be- lieved his quadrant’s error to be about −30″, instead of +1′ 30″ (or even +2′ 30″). To judge from the astronomical notebook, no further efforts to measure the pole height by means of the Sun were made, not even in late May or June, when the Sun was available day and night and the stars were in any case invisible.26 In conclusion, there is nothing in the sources to indicate that Hell bothered about the latitude any more after he had determined it by means of observa- tions of stars during the winter and early spring of 1769. It is a puzzle why Hell 25 and November 5, but then the subject is dropped and never mentioned again in this text. Sajnovics, travel diary, draft version (wus), October 14–November 5, 1768. 24 Hell’s MS “Observationes astronomicæ et Cæteræ in itinere litterario Viennâ Wardoëhu- sium usque factæ” (1768–69). wus. 25 Hell’s MS “Observationes astronomicæ […]” (1768–69): “[These observations] were also made with Mr. Niebuhr’s quadrant, which needs to be examined later.” 26 Further observations of solar heights recorded in the astronomical notebook are not con- cerned with the pole height. Thus, solar observations recorded on November 19–21, 1768 and January 19–21, 1769 contain deliberations concerning effects of the refraction upon the length of the polar night; various observations from January 24 to March 18, 1769 are either implicitly or explicitly undertaken in order to determine refraction; observations are conducted from April 10 to 26, 1769 in order to establish a correct meridian line for observations of magnetic declination; observations from April 29 to June 9, 1769 are evi- dently made in order to test the running of the clocks; and finally, observations in the night between June 17 and 18, 1769 have the additional aim of checking the refraction (the midnight Sun being very low above the sea level, this was a convenient crosscheck against the results obtained from observations of stars made earlier in the year).