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Roemer, Ole Christensen

1. Dates
Born: Aarhus, Denmark, 25 Sept 1644
Died: Copenhagen, 19 Sept 1710
Dateinfo: Dates Certain
Lifespan: 66
2. Father
Occupation: Merchant
Christen Pedersen Roemer was a small merchant.
It is known that when he died (1663 at the latest) he left Ole a great many navigational instruments and books; it appears then that he must have been, at the least, fairly well off. I will say, on the basis of this, affluent.
3. Nationality
Birth: Aarhus, Denmark
Career: Copenhagen, Denmark and France
Death: Copenhagen, Denmark
4. Education
Schooling: Copenhagen
1662, he was sent to the University of Copenhagen, where he studied with Thomas and Erasmus Bartholin. From what followed I assume a B.A.
5. Religion
Affiliation: Lutheran : Lutheran
6. Scientific Disciplines
Primary: Astronomy, Optics
Subordinate: Physics
7. Means of Support
Primary: Academia, Government, Patronage
He lived and studied with Erasmus Batholin, who was impressed enough with his work to entrust to him the editing of Tycho Brahe's manuscripts. From 1664 to 1670 he edited Tycho's manuscripts.
1671, he accompanied Bartholin and Jean Picard to Hveen to observe the position of Tycho's observatory, then (1672) accompanied Picard back to Paris where he was assigned lodgings in the Royal Observatory and worked under the auspices of the Académie. It is generally assumed that he was a member of the Académie. Louis XIV appointed him to tutor the Dauphin in astronomy, and Roemer travelled around France making observations at the behest of the Académie. Dansk Biografisk Leksikon says that he was admitted to the Académie in 1671.
1677, the Professorship of Astronomy in Copenhagen was designated for him. 1681, Professor of Mathematics, University of Copenhagen. He was also appointed astronomer royal and director of the observatory. In addition, he served in a number of advisory roles to the King, as master of the mint, harbor surveyor, inspector of naval architecture, ballistics expert, and head of a highway commission.
1688, member of the privy council.
1693, judiciary magistrate of Copenhagen.
1694, chief tax assessor.
1705, mayor of Copenhagen. Later, prefect of police as well.
1705, named a senator.
1706, head of the state council of the realm.
8. Patronage
Types: Scientist, Court Official
The first part of his life he was supported by scientists, first Bartholin, then Picard, who remained his patron after he settled in Paris. I assume some connection through the Académie got him Louis XIV's appointment as tutor. In 1704, long after his return to Denmark, he built his observatory on land owned by Erasmus Bartholin.
The major patron in his life was Christian V of Denmark who appointed him as astronomer royal and was responsible for the numerous appointments he held.
After Christian V died, Frederick IV assumed his patronage, first giving Roemer an appointment in 1705.
9. Technological Involvement
Types: Instruments, Civil Engineering, Hydraulics, Cartography
In Paris, part of his duties involved making instruments. He built clocks and other devices, including a micrometer for differential measurement of position. In Copenhagen, as director of the observatory he continued his innovation in instrumentation. He was perhaps the first to attach a telescopic sight to a meridian transit.
He also invented a new thermometer and was active in the science of thermometry, passing some ideas to Fahrenheit, whom he met in 1708.
Roemer reordered Denmark's system of measuring and registration and introduced a new, rational system for numbers and weights. The number and weight reforms were especially important because the confusion that existed before hampered trade. Roemer combined weight and length, a system which only occured in other lands more than a century later (with the metric system).
While Copenhagen was growing rapidly in these years, Roemer was in charge of laying out streets, lighting, water supply and drainage, fire standards, and lesser affairs.
In 1699, he revised the calendar, so that Easter was scheduled according to the moon.
10. Scientific Societies
Memberships: AR[?], Berlin Academy
He corresponded with Leibniz, Fahrenheit, and others.
Hoefer indicates he became a member of the Académie sometime around 1672, but the verbal records of the Académie for this period are missing and this piece of information is not generally mentioned in secondary sources.
Honorary member of the Berlin Academy.
  1. Hoefer, "Roemer," Nouvelle biographie universelle, 42, (Paris, 1862), cols. 495-7. [ref. CT143.H6] I.B. Cohen, Roemer and the First Determination of the Velocity of Light, (New York, 1944). [QC407.C67]
  2. Rene Taton, Roemer et la vitesse de la luminière, (Paris, 1978).
  3. [QC407.R63]
  4. Kirstine Meyer, "Roemer" [in Danish], Dansk Biografisk Leksikon, 20, (Copenhagen, 1941), 392-400. [CT1263.D2]
Compiled by:
Richard S. Westfall
Department of History and Philosophy of Science
Indiana University

Note: the creators of the Galileo Project and this catalogue cannot answer email on geneological questions.

©1995 Al Van Helden
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