Maximilianus Hell (1720-1792) - Munin

Lalande 1764), 36 9.26″ (Audiffredi 1766), 37 9.89″ (Hornsby 1763) 38 and 10.24″ (Pingré
1768), 39 i.e. a margin of error of more than 10 per cent, a far cry from the 0.2 per cent
predicted by Halley! In kilometres, the figures of Planman and Pingré equal 158,884,000 and
128,472,000 km respectively, an unacceptable degree of uncertainty to the contemporary
„quantifying spirit‟. 40
The three main sources of error mentioned above were also the „weapons‟ with which
astronomers attacked each other in the ensuing debates after the 1761 transit. In order to bring
all the data into harmony, it was necessary to consider some features of various observations
doubtful. The longitude might have been erroneously determined, the clocks wrongly adjusted
or the practical skills of the observer(s) insufficient. Given the ambition, publicity and the
sheer amount of money invested in the project, it may well be that such assessments aroused a
certain degree of anger among those whose observations were deemed unreliable. However,
judging from the tone of the main papers on the solar parallax published in the aftermath of
1761, it seems to be an exaggeration to describe this as a “quarrel between French and British
astronomers”. 41 Quite the contrary: astronomers involved were generally careful to use polite
language when discussing the observations and/or calculations of their colleagues. With
hindsight, we may conclude that this strategy was a prudent one: most astronomical data sets
are useless when not compared with other observations. 42 Cutting off correspondence with a
36
Hell 1763, p. 225: “Ex his omnibus concludendum arbitror, interea, dum Anno 1769. iterum instituatur
observatio transitus ♀ per discum ʘ, assumendam ex omnibus arithmetice mediam Parallaxim, scilicet = 9″.0.”
= “based on all these [i.e., observations] I think we may – while we are waiting for the year 1769, when another
transit of Venus across the disc of the Sun will be observed – draw the temporary conclusion that an
arithmetically deduced mean parallax should be assumed, namely, 9.00 seconds”; Lalande 1764, p. 800: “en
attendant que le passage de 1769 nous ait donné à ce sujet de nouvelles lumieres, nous nous en tiendrons à faire
la parallaxe moyenne du soleil de 9″” = “while waiting for the time when the passage of 1769 will have shed
new light on this issue, we draw the conclusion of a mean solar parallax of 9 seconds”.
37
Audiffredi‟s mean value of the solar parallax as calculated in De Solis parallaxi ad V. Cl. Grandjean de
Fouchy … Commentarius, Rome 1766, was – according to Pigatto 2005, p. 83 – 9″.26 (i.e., 9.26 seconds).
38
Hornsby 1764, p. 494: “such different methods give a parallax of the Sun on the day of the transit equal to
9″,736”. This represents a mean horizontal parallax of 9.89 seconds; cf. Verdun 2004, p. 12.
39
Pingré 1768, p. 32: “en excluant toutes celles que j‟ai marquées comme douteuses, la parallaxe est de 10″,24”
= “when all those [i.e., observations] that I have marked as dubious are excluded, the parallax is 10.24 seconds”,
cf. p. 23: “Si je persiste à croire que la parallaxe horizontale du Soleil est d‟environ 10 secondes ¼ , c‟est que
mon observation ne me permet de penser autrement” = “when I persist in believing that the horizontal parallax of
the Sun is about 10¼ seconds, I do so because my observation does not permit me to think otherwise” (cf. Pingré
1763, p. 486, where the mean horizontal parallax is stated to be as high as 10.60″).
40
I am indebted to Truls Lynne Hansen (pers. comm.) for calculating these figures, using the present value of
Earth‟s equator radius (6,378 km).
41
Chr. Mayer Ad Augustissimam ... Expositio de transitu Veneris ... 1769b, Praefatio, p. [v]: “inter Anglos
Gallosque ex obseruationibus anni 1761 natam de parallaxi horizontali controuersiam”; cf. Hell, De Parallaxi
Solis … 1772, pp. 113-114, where he speaks of lites litterariae (“scientific quarrels”) between French and British
astronomers after the transit of 1761.
42
For more on this aspect of early-modern astronomy, see for example Widmalm 1991 & 1992; Brosche 2009b.
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