Horologium

Hor star chart. (IAU and Sky & Telescope magazine: Roger Sinnott & Rick Fienberg)

One of the 88 IAU constellations. It was invented by Lacaille and published in his 1756 report to the French Academy of Science, republished in 1763.

Etymology and History

Lacaille on Horologium (1756)

In his first publication in 1756 Lacaille writes in French:

• L’Horloge à pendule & à secondes (translated: the pendulum clock which is accurate to the second)

He depicted an instrument with two pendulums (and not only one) suggesting that the high accuracy is achieved by the second pendulum for the seconds.

Origin of Constellation

It is not known why Nicolas de Lacaille conceived this constellation in the sky. In any case, he brought it back from his expedition to South Africa in 1750-'54 and published it in 1756. Ian Ridpath believes that it is the pendulum clock in his South African observation station because Horologium is depicted next to Reticulum and therefore the two instruments belong together. With this interpretation, "Horologium" would be a Le Roy-clock. There is nothing to be said against this idea, but in general Lacaille did not take care to ensure that neighbouring pictures were necessarily connected. Furthermore, the Reticulum (Net) is not really Lacaille's invention but a transformed take-over from the Strasbourg-mathematician Isaac Habrecht. Hence, there is therefore no strong argument in favour of this idea.

Considering the historical period in which Lacaille lived, it might be equally obvious that the marine chronometer should be considered here. John Harrison, who is celebrated in today's popculture as ‘the solitary genius who solved one of the greatest problems of his time’, was the first person to win the English ‘Board of Longitude’ prize in 1737. This was the most important prize awarded by the English crown at the time, and was awarded in 1714 for the discovery of a method of determining longitude on the high seas. However, Harrison became posthumusly much more known than in his lifetime, and it is unknown whether Lacaille would have had the chance to know about the early etaps of his achievements: the final award was given to him only in 1773 (twenty years after Lacaille's stay in Cape Town). Lacaille could only have thought of the topic (or dream) of a high precision pendulum clock and not of a real piece. Hence, Geymeier and Hoffmann (2023) conclude that this hyposthesis similarly vague as the above: "As he had never seen a Harrison clock, he could not have been depicted one, but at most a desire for such a precision instrument (and second pendulums are the most accurate he knew)."

Transfer and Transformation of the Constellation

• 

  Lacaille's Horologium (1763)

• 

  Horologium in Bode's "Anleitung zur Kenntniß des gestirnten Himmels" (1782).

• 

  Goldbach's Horologium (1799) exactly reproduced from Lacaille.

Mythology

There is no mythology except the above speculations about Lacaille's intensions.

References

• References (general)
• References (medieval)