Maximilianus Hell (1720-1792) - Munin

data that were used for the computation of the solar parallax. 29 The vast majority of the
observers who embarked upon expeditions for this occasion were French or British. A mappe-
monde indicating where the transit would be visible had been issued by French astronomers
and given world-wide distribution ahead of the transit, 30 and astronomers took up positions in
places such as Tobolsk and Selenginsk in Siberia, Rodrigues in the Indian Ocean, Pondicherry
in India and St. Helena in the Southern Atlantic, as well as numerous locations in Europe.
In 1716, Halley had stated that previous attempts to determine the Earth-Sun distance by well-
known astronomers such as Tycho Brahe, Copernicus, Kepler and Riccioli had resulted in a
distance ranging from 1,200 Earth radii up to 7,000 (“Earth radii” = semidiameters of the
Earth). By contrast, he anticipated that his own method would result in a calculation of the
solar distance with a margin of error of no more than 0.2 per cent. 31 However, given the
sources of error listed above, it should come as no surprise that computations of the solar
parallax based on all the 1761 observations varied from 8.28″ (Planman 1769), 32 8.33″
(Rumovskii 1767), 33 8.615″ (Röhl 1768) 34 and 8.69″ (Short 1764) 35 to 9.00″ (Hell 1763,
29 Woolf 1959, pp. 135-141.
30 Reprint in Woolf 1959, Fig. 8, between pp. 98-99, cf. the distribution list on pp. 209-211.
31 Halley in Sellers 2001, p. 211: “We have now shewn, that by this method the Sun‟s parallax may be
investigated to within its five hundredth part” = Halley 1717, p. 460: “Diximus autem hac ratione Solis
Parallaxin intra quingentesimam sui partem investigari posse”.
32 Planman 1769 (paper written in 1767), p. 127: “Hinc iterum per medium habetur solis parallaxis 8″,49.
Rejecta autem columna tertia, ceu maxime discrepante, dabunt reliquæ solis parallaxin 8″,30, quæ cum parum
admodum abludat ab ista 8″,28, quam maximi momenti observationes præbebant […]; vi novissimi transitus
Veneris, parallaxis solis horizontalis quam proxime statuenda est 8″,28” = “Thus, once again we have a solar
parallax of 8.49 seconds. However, if the third column [of calculations], being the most divergent, is rejected, the
rest will give a solar parallax of 8.30 seconds. Since this parallax is so little at variance with the above-stated
parallax of 8.28 seconds, which the most important observations gave us […], the horizontal parallax of the Sun,
on the basis of the latest transit of Venus, should be stated to be very close to 8.28 seconds”.
33 Rumovskii 1767b, p. 510: “Omnes itaque obseruationes a me in computum ductae, eo gradu in statuenda Solis
parallaxi consentiunt, vt pleraeque non nisi in centesimis minuti secundi partibus discrepent, atque minima a
maxima non nisi 0″.36 […]. Mediam itaque ex his determinationibus quantitatem 8″.33 pro vera magnitudine
parallaxeos assumere iure possumus” = “Thus, all the observations that I have used for the computation, are in
harmony with each other for the fixing of the Sun‟s parallax to such a degree that in most cases there is a
discrepancy of only a hundredth part of a second between them, and the difference between the smallest and the
largest is only 0.36 seconds. Hence, the mean quantity of all the determinations – 8.33 seconds – we may justly
assume to be the true magnitude of the parallax”.
34 Röhl 1768, p. 110: “Jch habe aus allen diesen Beobachtungen aus dem Grade der Zuverläßigkeit, welches sie
in Ansehung der Parallaxe geben, und welche ohne Zweifel dem Unterscheide der Zwischenzeit zwischen den
Beobachtungen proportionirlich ist, das Mittel gesucht, und da finde ich noch 8″,615 wie vorher” = “From all
these observations [i.e., of the transit of Venus] I have sought the mean value, according to the degree of
reliability that they convey as regards the parallax, and which certainly is proportional to the interval of time
between the observations; and again I find 8.615 seconds, just like before”.
35 Short 1764, p. 340: “Thus is the Sun‟s parallax, on the day of the transit, concluded to be = 8″,56 [i.e., a mean
horizontal parallax of 8.69 seconds; cf. Verdun 2004, p. 12], and that from three different modes of comparing
together a great number of observations variously combined” (cf. Short 1763, p. 621: “The parallax of the Sun
being thus found, by the observations of the interior contact at the egress = 8″,52 on the day of the transit, the
mean horizontal parallax of the Sun is = 8″,65”).
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