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Letter from Ole Christensen Römer (1644-1710), Danish astronomer and physicist, 18th September 1679
(Detta inlägg finns endast i engelsk version)

The document is written in French and states that after supper Rømer will proceed to observatory to watch the two eclipses of the moons of Jupiter. The addressee is invited to join him in his observations. The document is dated September 18th [1679].

Signum/Shelfmark:  Waller Ms dk-01907
The letter in digital form: Letter 1679-09-18, Paris



Lundy 18 Sept.


Il y a demain au soir entre 9 et 10 heures des merveilles a voir dans le ciel de jupiter,
scavoir deux eclipses des satellites.
Je dois soupper chez president Bignon, d’ou je sortiray infalliblement a 9 heures precis,
et un peu avant si cela se pourra[.] Sur le neuf heure un qvarre vous trouverez toute
preste a l’observatoire, si vous vous voulez donner la peine d’y venir.

Je suis le Vostre entierement


Ole Christensen Rømer

Ole Christensen Rømer (1644-1710) studied under Rasmus Bartholin at the University of Copenhagen from 1662 to 1671. Between 1672 and 1681 he worked at the Paris Observatory, where he made the observations that led him to conclude that the speed of light was not infinite. Having returned to Copenhagen in 1681 Rømer took up the post of professor at the university, to which he had been appointed in 1676. In Copenhagen Rømer built observatories and made instruments (e.g. the meridian circle), standardised measures and weights, and saw to it that the calendar reform was introduced in 1700. G. D. Fahrenheit’s thermometer was inspired by one made by Rømer. He became chief constable and mayor of Copenhagen (1705).

Among his acqaintances and correspondents in the scientific and scholarly community were Christiaan Huygens, G. W. Leibnitz, John Locke, John Flamsteed and Edmund Halley. The rivalry between J-D Cassini and Rømer is well documented. Rømer twice, in 1681 and 1699, married into the influential Bartholin family.

The addressee

Nicolas Toinard (Thoynard) (1629-1706) was a French antiquary proficient in ancient languages and a numismatist. He published a Greek concordance to the gospels and dissertations on Lactantius and Roman medals. As seen from Waller Ms dk-01906 he seems to have had some knowledge of cannons and guns. He was a friend of John Locke, whom he met in Paris in 1677. It was through Toinard that Rømer made Locke’s acquaintance.

Other Rømer documents in the Waller Collection

One of the other two documents  in the Waller collection written by Rømer, Waller Ms dk-01906, mentions a hitherto unknown brother of the author. The other one is dated 1680, Waller Ms dk-01905.

Text and transcription: Bo Jaensson
Image: Uppsala University Library/Uppsala universitetsbibliotek (Alvin)

Detta inlägg har tidigare publicerats på Uppsala universitetsbiblioteks webbplats 2014 / This post has previously been published on the Uppsala University Library’s website 2014.