Maximilianus Hell (1720-1792) - Munin

himself, along with Rødkier, Ahl, Peder Horrebow the Younger and a Christian Boserup –
thought they could verify the existence of a moon of Venus by means of a 9½-foot telescope
at the Rundetårn. Accordingly, Chr. Horrebow reported their findings in the Gazette littéraire
de l’Europe of 18 April 1764, as well as at lectures held at the Royal Society of Copenhagen
that were published in its proceedings. 85 However, these observations were placed under
scrutiny by Maximilianus Hell and elegantly refuted as mere optical illusions in his treatise
„On the Moon of Venus‟ (see Section II.1.4). 86
In order to contribute to the Venus transit project, not too much skill was required. The most
important thing was to be in possession of a good astronomical tube and a reliable clock for
the time-keeping. In principle, it was possible to learn the rest within a few weeks or months
of practice. 87 Arguably, Denmark-Norway as a seafaring nation had an unexploited resource
in their captains of ships, in the navy for example, since a rudimentary knowledge at least of
practical astronomy was required in order to navigate on the open sea. Furthermore, the 1761
transit took place in the midst of a joint Swedish-Danish project of geodesy, by which various
surveyors were measuring the still undetermined border between Norway and Sweden/Fin-
land. 88 This also meant that there were experienced surveyors around – another unexploited
resource for the Danish Venus transit project of 1761. In Sweden an amateur of astronomy
and veteran of the boundary surveying, Hellant in Torneå, was not only invited to participate,
but was even sponsored by the Royal Academy to do so (Section I.2.1). Other participants on
the Swedish side were various captains of ships, teachers at academies and colleges, and at
85 Rødkier, “Beretning om een den 3 og 4 Martii 1764. giort Jagttagelse, angaaende Veneris Drabant” 1765; Chr.
Horrebow, “Reflexioner, anlangende Veneris Drabant” 1765a & “Videre Fortsættelse af Observationerne giorte
paa Veneris Drabant” 1765b. It is known that Horrebow received a copy of Baudouin‟s memoir on the satellite
of Venus just after it had been published, from the Swedish astronomer Bengt Ferner (or Ferrner, 1724-1802)
who was in Paris at the time (Ferner‟s diary, entries 20-24 May 1761 = Ferrner 1956, pp. 388-390).
86 Hell 1765, espec. pp. 25-26 & 83-84. For a more elaborate account of the observations and deliberations of
Horrebow and other Danish astronomers, see now Kragh 2008, espec. pp. 59-67.
87 That laymen were in fact encouraged to participate in the project is evident from the pedagogical nature of
writings such as Hell‟s Transitus Veneris per discum Solis Anni 1761 … 1760; Martin, Venus in the Sun: being
an Explanation of the Rationale of that great Phænomenon … 1760; Ferguson, A Plain Method of Determining
the Parallax of Venus by her Transit over the Sun 1760 (cf. Sellers 2001, pp. 122-123); Röhl, Merkwürdigkeiten
von den Durchgängen der Venus durch die Sonne 1768; Maskelyne, Instructions Relative to the Observation of
the Ensuing Transit of Venus over the Sun’s Disk … 1768; [Anonymous], A Copper Plate and Discourse of the
Transit of Venus, On the 3d of June 1769 … [1769]; etc. In 1769, Hell allowed the natural historian
Borchgrevink to use one of his three telescopes to observe the transit, despite the fact that Borchgrevink had no
previous experience in astronomy (see Section II.3.2). Another natural historian and pupil of Linnaeus, Daniel
Solander (1733-1782), was also observing the transit alongside Captain Cook and the astronomer Green on
Tahiti, presumably without having any previous experience in astronomy either (Cook 1772).
88 A border treaty was signed between the two countries in 1751. In an additional document (kodicill), it was
agreed that the border measurements which had started during the 1740s were to continue for seven more years
(in fact, the measurements were not finished until 1767; see for example Tobé 1991, pp. 59-61).
- 243 -