Editing Ole Rømer

{{Short description|Danish astronomer (1644–1710)}}
{{Redirect|Rømer}}
{{Use dmy dates|date=August 2023}}
{{Infobox scientist
| name              = Ole Rømer
| image             = Rømer, Ole (ur Berømte danske maend).jpg
| image_size        = 
| caption           = Ole Rømer, portrait by [[Jacob Coning]] from c. 1700
| birth_name        = Ole Christensen Rømer
| birth_date        = {{Birth date|1644|9|25|df=yes}}
| birth_place       = [[Aarhus]], [[Denmark–Norway]]
| death_date        = {{Death date and age|1710|9|19|1644|9|25|df=yes}}
| death_place       = [[Copenhagen]], [[Denmark–Norway]]
| residence         = 
| citizenship       = 
| nationality       = Danish
| ethnicity         = 
| field             = [[Astronomy]]
| work_institutions = 
| alma_mater        = [[University of Copenhagen]]
| doctoral_advisor  = 
| doctoral_students = 
| known_for         = [[Rømer's determination of the speed of light]]<br>[[Rømer scale]]<br>[[Cycloid gear]]<br>[[Light-time correction]]<br>[[Altazimuth mount]]<br>[[Meridian circle]]
| author_abbrev_bot = 
| author_abbrev_zoo = 
| influences        = 
| influenced        = 
| awards            = 
| footnotes         = 
| signature         = Ole Rømer Signature.svg
}}

'''Ole Christensen Rømer''' ({{IPA|da|ˈoːlə ˈʁœˀmɐ|lang}}; 25 September 1644 – 19 September 1710) was a [[Danes|Danish]] [[astronomer]] who, in 1676, first demonstrated that light travels at a finite speed. Rømer also invented the modern thermometer showing the temperature between two fixed points, namely the points at which [[water]] respectively boils and freezes.

Rømer made his discovery regarding the [[speed of light]] while working at the [[Paris Observatory|Royal Observatory in Paris]] and studying [[Jupiter]]'s moon [[Io (moon)|Io]]. He estimated that light takes about 11 minutes to travel from the Sun to Earth. Using today's knowledge of the [[Astronomical unit|Sun-Earth distance]], this would amount to a speed of light of approximately 220,000 kilometers per second,<ref>{{Cite journal |last=van Helden |first=Albert |date=1983 |title=Roemer's Speed of Light |url=https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1983JHA....14..137V&db_key=AST&page_ind=0&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES |journal=Journal for the History of Astronomy |language=en |volume=14 |issue=2 |pages=137–141 |doi= 10.1177/002182868301400206|bibcode=1983JHA....14..137V |issn=}}</ref> compared to today's accepted value of just under 300,000 kilometers per second.

In scientific literature, alternative spellings such as "Roemer", "Römer", or "Romer" are common.

== Biography ==
[[File:Rundetårn over rooftops.JPG|thumb|''[[Rundetårn]]'' ("round tower") in [[Copenhagen]], on top of which the university had its observatory from the mid 17th century until the mid 19th century when it was moved to new premises. The current observatory there was built in the 20th century to serve amateurs.]]
Rømer was born on 25 September 1644 in [[Aarhus]] to merchant and skipper Christen Pedersen (died 1663), and Anna Olufsdatter Storm ({{Circa|1610}} – 1690), daughter of a well-to-do [[alderman]].<ref name="Dalgaard1996">{{cite book
| author    = Niels Dalgaard
| title     = Dage med Madsen, eller, Livet i Århus: om sammenhænge i Svend Åge Madsens forfatterskab
| url       = https://books.google.com/books?id=wunQTxJQAA8C&pg=PA169
| date      = 1996
| publisher = Museum Tusculanum Press
| language  = da
| isbn      = 978-87-7289-409-6
| pages     = 169–
| quote     = ... skipper og handelsmand i Århus, gift med Anne Olufsdatter Storm (død 1690) og far til astronomen Ole Rømer (1644–1710).
}}</ref> Since 1642, Christen Pedersen had taken to using the name Rømer, which means that he was from the Danish island of [[Rømø]], to distinguish himself from a couple of other people named Christen Pedersen.<ref>{{cite book
| last      = Friedrichsen
| first     = Per
| author2   = Tortzen, Chr. Gorm
| title     = Ole Rømer&nbsp;– Korrespondance og afhandlinger samt et udvalg af dokumenter
| date      = 2001
| publisher = C. A. Reitzels Forlag
| location  = Copenhagen
| language  = da
| isbn      = 87-7876-258-8
| pages     = 16
}}</ref> There are few records of Ole Rømer before 1662, when he graduated from the old [[Aarhus Katedralskole]] (the [[Cathedral school]] of Aarhus),<ref>{{cite book
| title     = Bogvennen
| url       = https://books.google.com/books?id=Ply5AAAAIAAJ
| volume    = 1-9
| date      = 1971
| publisher = Fischers forlag
| language  = da
| pages     = 66–
| quote     = Denne antagelse tiltrænger en nærmere redegørelse: Ole Rømer udgik som student fra Aarhus Katedralskole i 1662. Ole Rømer Skolens rektor på den tid var Niels Nielsen Krog, om hvem samtidige kilder oplyser, at "hans studium ...
}}</ref><ref name="LindHenriksen2003">{{cite book
 |author1   = Olaf Lind
 |author2   = Poul Ib Henriksen
 |title     = Arkitektur Fortaellinger/Building of Aarhus University
 |url       = https://books.google.com/books?id=BtxKO1PzadgC&pg=PA21
 |date      = 2003
 |publisher = Aarhus Universitetsforlag
 |language  = da
 |isbn      = 978-87-7288-972-6
 |pages     = 21–
 |quote     = Ole Rømer tog iøvrigt studentereksamen fra Latinskolen i Århus (Katedralskolen) i 1662.
}}{{Dead link|date=February 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> moved to Copenhagen and matriculated at the [[University of Copenhagen]]. His mentor at the University was [[Rasmus Bartholin]], who published his discovery of the [[double refraction]] of a light ray by [[Iceland spar]] (a transparent form of the mineral [[calcite]]) in 1668, while Rømer was living in his home. Rømer was given every opportunity to learn mathematics and astronomy using [[Tycho Brahe]]'s astronomical observations, as Bartholin had been given the task of preparing them for publication.<ref>Friedrichsen; Tortzen (2001), pp. 19–20.</ref>

Rømer was employed by the French government: [[Louis XIV of France|Louis XIV]] made him tutor for the [[Dauphin of France|Dauphin]], and he also took part in the construction of the magnificent [[fountain]]s at [[Palace of Versailles|Versailles]].

In 1681, Rømer returned to Denmark and was appointed professor of [[astronomy]] at the University of Copenhagen, and the same year he married Anne Marie Bartholin, the daughter of [[Rasmus Bartholin]]. He was active also as an observer, both at the University [[Observatory]] at [[Rundetårn]] and in his home, using improved instruments of his own construction. Unfortunately, his observations have not survived: they were lost in the great [[Copenhagen Fire of 1728]]. However, a former assistant (and later an astronomer in his own right), [[Peder Horrebow]], loyally described and wrote about Rømer's observations.

In Rømer's position as royal mathematician, he introduced the first national system for weights and measures in Denmark on 1 May 1683.<ref name="SchultzDahlberg2013">{{cite book
| author1   = Mai-Britt Schultz
| author2   = Rasmus Dahlberg
| title     = Det vidste du ikke om Danmark
| url       = https://books.google.com/books?id=paqvAQAAQBAJ&pg=PT53
| date      = 31 October 2013
| publisher = Gyldendal
| language  = da
| isbn      = 978-87-02-14713-1
| pages     = 53–
| quote     = I 1683 udarbejdede Ole Rømer en forordning, der fastsatte den danske mil samt en række andre mål, hvilket var hårdt tiltrængt, for indtil da havde der hersket et sandt enhedskaos i Danmark/Norge. Eksempelvis var en sjællandsk alen 63 centimeter, ...
}}</ref><ref name="ChristiansenRiis1982">{{cite book
| author1   = Poul Aagaard Christiansen
| author2   = Povl Riis
| author3   = Eskil Hohwy
| title     = Festskrift udgivet i anledning af Universitetsbibliotekets 500 års jubilæum 28. juni 1982
| url       = https://books.google.com/books?id=teoYAAAAIAAJ
| date      = 1982
| publisher = Lægeforeningen
| language  = da
| pages     = 87–
| quote     = En studie i Ole Rømers efterladte optegnelser, Adversaria, som hans enke Else Magdalene ... at give Christian V's kongelige mathematicus Ole Rømer (1644–1710) æren for udformningen af forordningen af 1.V.1683 ...
}}</ref> Initially based on the Rhine foot, a more accurate national standard was adopted in 1698.<ref name="Thomas2010">{{cite book
| author    = Alastair H. Thomas
| title     = The A to Z of Denmark
| url       = https://books.google.com/books?id=MKH4JuPT6boC&pg=PA422
| date      = 10 May 2010
| publisher = Scarecrow Press
| isbn      = 978-0-8108-7205-9
| pages     = 422–
| quote     = ... although uniformity throughout the country was not achieved until statutes of 1683 and 1698, under the leadership of Ole Romer. The metric system was adopted in 1907 and is universal, though colloquially units such as tomme, tønde land, ...
}}</ref> Later measurements of the standards fabricated for length and volume show an excellent degree of accuracy. His goal was to achieve a definition based on astronomical constants, using a [[pendulum]]. This would happen after his death as practicalities made it too inaccurate at the time. Notable is also his definition of the new [[Danish units of measurement|Danish mile]] of 24,000 Danish feet (circa 7,532&nbsp;m).<ref name="Nørlund1944">{{cite book
| author    = Niels Erik Nørlund
| title     = De gamle danske længdeenheder
| url       = https://books.google.com/books?id=DGvnAAAAMAAJ
| date      = 1944
| publisher = E. Munksgaard
| language  = da
| pages     = 74–
| quote     = ... Maj 1683 gennemførte Reform af Maal og Vægt fastsatte Ole Rømer den danske Mils Længde til 12 000 danske Alen.
}}</ref>

In 1700, Rømer persuaded the king to introduce the [[Gregorian calendar]] in [[Denmark-Norway|Denmark and Norway]]&nbsp;– something [[Tycho Brahe]] had argued for in vain a hundred years earlier.<ref name="Tjørnhøj-Thomsen2011">{{cite book
| author    = K. Hastrup
| author2   = C. Rubow
| author3   = T. Tjørnhøj-Thomsen
| title     = Kulturanalyse&nbsp;– kort fortalt
| url       = https://books.google.com/books?id=HIA_ZrqlPSkC&pg=PA219
| date      = 2011
| publisher = Samfundslitteratur
| language  = da
| isbn      = 978-87-593-1496-8
| pages     = 219–
| quote     = I Danmark blev den gregorianske kalender indført den 1. marts 1700 efter forarbejde af Ole Rømer. Man stoppede med brug af den julianske kalender den 18. februar, og sprang simpelthen de næste 11 dage over, så man landede direkte på  ...
}}</ref>

[[File:Ole Rømer at work.jpg|thumb|left|200px|Ole Rømer at work]]
Rømer developed a [[temperature]] scale while convalescing from a broken leg.<ref name="Shachtman2000">{{cite book
| author    = Tom Shachtman
| title     = Absolute Zero and the Conquest of Cold
| url       = https://books.google.com/books?id=IJ91od-UYygC
| date      = 12 December 2000
| publisher = Houghton Mifflin Harcourt
| isbn      = 0-547-52595-8
| pages     = 48–
| quote     = ... down to an almost mythical point, an absolute zero, the end of the end. Around 1702, while Amontons was doing his best work in Paris, in Copenhagen the astronomer Ole Romer, who had calculated the finite speed of light, broke his leg. Confined to his home for some time, he took the opportunity of forced idleness to produce a thermometer having two fixed points ...
}}</ref> After visiting with Rømer in 1708, [[Daniel Gabriel Fahrenheit]] began making his thermometers using a modified version of [[Rømer scale|Rømer's scale]] that eventually evolved into the [[Fahrenheit scale]] still popular in the United States and a few other countries.<ref name="Rittner2009">{{cite book
| author    = Don Rittner
| title     = A to Z of Scientists in Weather and Climate
| url       = https://books.google.com/books?id=nU_jIyhvKOUC&pg=PA54
| date      = 1 January 2009
| publisher = Infobase Publishing
| isbn      = 978-1-4381-0924-4
| pages     = 54–
| quote     = Fahrenheit's first thermometers, from about 1709 to 1715, contained a column of alcohol that directly expanded and contracted, based on a design made by Danish astronomer Ole Romer in 1708, which Fahrenheit personally reviewed. Romer ...
}}</ref><ref>{{cite book
| title     = Popularization and People (1911–1962)
| url       = https://books.google.com/books?id=dpb1GaDPoq0C&pg=PA431
| date      = 22 October 2013
| publisher = Elsevier
| isbn      = 978-0-08-046687-3
| pages     = 431–
| quote     = ... letter from Fahrenheit to his Dutch colleague Hermann Boerhaave (1668–1738) dated 17 April 1729 in which Fahrenheit describes his experience at Rømer's laboratory in 1708.
}}</ref><ref name="SchlagerLauer2001">{{cite book
| author1   = Neil Schlager
| author2   = Josh Lauer
| title     = Science and Its Times: 1700–1799
| url       = https://books.google.com/books?id=6I1FAAAAYAAJ
| date      = 2001
| publisher = Gale Group
| isbn      = 978-0-7876-3936-5
| pages     = 341–
| quote     = In 1708 Fahrenheit visited Ole Romer (1644–1710). Since at least 1702 Romer had been making alcohol thermometers with two fixed points and a scale divided into equal increments. He impressed upon Fahrenheit the scientific importance of ...
}}</ref>

Rømer also established navigation schools in several Danish cities.<ref name="PetersenAndersen1929-715">{{cite book
| author1   = Carl Sophus Petersen
| author2   = Vilhelm Andersen
| author3   = Richard Jakob Paulli
| title     = Illustreret dansk litteraturhistorie: bd. Den danske littterature fra folkevandringstiden indtil Holberg, af C.S. Petersen under medvirkning af R. Paulli
| url       = https://books.google.com/books?id=9MUSAAAAMAAJ
| date      = 1929
| publisher = Gyldendai
| language  = da
| pages     = 716–
| quote     = ... Det var paa hans Tilskyndelse, at de første Navigationsskoler (i København og Stege) oprettedes, og Bestyrerpladserne besatte han med de bedste ...
}}</ref>

In 1705, Rømer was made the second Chief of the Copenhagen [[Police]], a position he kept until his death in 1710.<ref name="SarlemijnSparnaay2013">{{cite book
| author1   = A. Sarlemijn
| author2   = M.J. Sparnaay
| title     = Physics in the Making: Essays on Developments in 20th Century Physics
| url       = https://books.google.com/books?id=B_FGBQAAQBAJ&pg=PA48
| date      = 22 October 2013
| publisher = Elsevier Science
| isbn      = 978-1-4832-9385-1
| pages     = 48–
| quote     = The other, Ole Rømer, was Bartholin's amanuensis, later his son-in-law. ... man, became the Danish king's mathematician (mathematicus regius), professor of astronomy at the University of Copenhagen, and eventually chief of police of that city.
}}</ref> As one of his first acts, he fired the entire force, being convinced that the morale was alarmingly low. He was the inventor of the first street lights (oil lamps) in Copenhagen, and worked hard to try to control the beggars, poor people, unemployed, and prostitutes of Copenhagen.<ref name="informationsafdelingen1970">{{cite book
| author    = Denmark. Udenrigsministeriet. Presse- og informationsafdelingen
| title     = Denmark. An official handbook
| url       = https://books.google.com/books?id=FuoiAQAAIAAJ
| date      = 1970
| publisher = Krak
| isbn      = 978-87-7225-011-3
| pages     = 403–
| quote     = It was perhaps fortunate that Ole Romer (1644–1710) was called home to Denmark after he had achieved world fame by ... of Copenhagen and oblige him to devote time and energy to thinking out measures against prostitution and begging.
}}</ref><ref name="OlsenAskgaard1985">{{cite book
| author1   = Gunnar Olsen
| author2   = Finn Askgaard
| title     = Den unge enevaelde: 1660–1721
| url       = https://books.google.com/books?id=XAsWAQAAMAAJ
| date      = 1985
| publisher = Politikens Forlag
| language  = da
| isbn      = 978-87-567-3866-8
| pages     = 368–
| quote     = Det var et held, at Ole Rømer først blev kaldt tilbage til den danske hovedstad, efter at han i Paris havde opnået ... Men at denne geniale forsker som Københavns politimester skulle beskæftige sig med forholdsregler mod prostitution og betleri, ..
}}</ref>

In Copenhagen, Rømer made rules for building new houses, got the city's water supply and sewers back in order, ensured that the city's fire department got new and better equipment, and was the moving force behind the planning and making of new pavement in the streets and on the city squares.<ref name="Samfund1914">{{cite book
| author    = Danmarks Naturvidenskabelige Samfund
| title     = Ingeniørvidenskabelige skrifter
| url       = https://books.google.com/books?id=vldVAAAAMAAJ
| date      = 1914
| publisher = Danmarks naturvidenskabelige samfund, i kommission hos G.E.C. Gad
| language  = da
| pages     = 108–
| quote     = I de følgende Aar udstedtes der en Række Forordninger om Gaderne; de skyldes uden Tvivl Ole Rømer. Snart er det Brolægningen, det gælder, snart et omhyggeligt Reglement for Færdslen i Gaderne. Brolægningen havde medført store ...
}}</ref><ref name="Bech1967">{{cite book
| author    = Svend Cedergreen Bech
| title     = Københavns historie gennem 800 år
| url       = https://books.google.com/books?id=8F4QAQAAIAAJ
| date      = 1967
| publisher = Haase
| language  = da
| pages     = 246–
| quote     = 1705-10 beklædtes politimesterembedet af fysikeren Ole Rømer, i hvis embedstid mange reformer forsøgtes. Brolægning og belysning forbedredes, vandforsyning og vandafledning blev taget op til revision, men heller ikke en så ...
}}</ref><ref name="Kjerulf1964">{{cite book
| author    = Axel Kjerulf
| title     = Latinerkvarteret; blade af en gemmel bydels historie
| url       = https://books.google.com/books?id=xTDTAAAAMAAJ
| date      = 1964
| publisher = Hassings forlag
| language  = da
| pages     = 44–
| quote     = Ole Rømer vendte i 1681 tilbage til København, hvor han blev professor i astronomi ved universitetet og giftede sig med Rasmus ... justering af mål og vægt, blev ham betroet foruden ordning af byggeforhold, gaders brolægning og belysning.
}}</ref>

Rømer died at the age of 65 in 1710. He was buried in [[Church of Our Lady (Copenhagen)|Copenhagen Cathedral]], which has since been rebuilt following its destruction in the [[Battle of Copenhagen (1807)]]. There is a modern memorial.<ref name="TrimbleWilliams2007">{{cite book
| author1   = Virginia Trimble
| author2   = Thomas R. Williams
| author3   = Katherine Bracher
| author4   = Richard Jarrell
| author5   = Jordan D. Marché
| author6   = F. Jamil Ragep
| title     = Biographical Encyclopedia of Astronomers
| url       = https://books.google.com/books?id=t-BF1CHkc50C&pg=PA983
| date      = 18 September 2007
| publisher = Springer Science & Business Media
| isbn      = 978-0-387-30400-7
| pages     = 983–
}}</ref>

== Rømer and the speed of light ==
{{Main|Rømer's determination of the speed of light}}
The determination of [[longitude]] is a significant practical problem in [[cartography]] and [[navigation]]. [[Philip III of Spain]] offered a prize for a method to determine the longitude of a ship out of sight of land, and [[Galileo Galilei|Galileo]] proposed a method of establishing the time of day, and thus longitude, based on the times of the eclipses of the moons of [[Jupiter]], in essence using the Jovian system as a cosmic clock; this method was not significantly improved until accurate mechanical clocks were developed in the eighteenth century. Galileo proposed this method to the Spanish crown (1616–1617) but it proved to be impractical, because of the inaccuracies of Galileo's timetables and the difficulty of observing the eclipses on a ship. However, with refinements, the method could be made to work on land.

After studies in Copenhagen, Rømer joined [[Jean Picard]] in 1671 to observe about 140 eclipses of Jupiter's moon [[Io (moon)|Io]] on the island of [[Hven]] at the former location of [[Tycho Brahe]]’s observatory of [[Uraniborg]], near Copenhagen, over a period of several months, while in Paris [[Giovanni Domenico Cassini]] observed the same eclipses. By comparing the times of the eclipses, the difference in longitude of Paris to Uraniborg was calculated.

Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed. In 1672 Rømer went to Paris and continued observing the satellites of Jupiter as Cassini's assistant. Rømer added his own observations to Cassini's and observed that times between eclipses (particularly those of Io) got shorter as Earth approached Jupiter, and longer as Earth moved farther away. Cassini made an announcement to the Academy of Sciences on 22 August 1676:

<blockquote>''This second inequality appears to be due to light taking some time to reach us from the satellite; light seems to take about ten to eleven minutes [to cross] a distance equal to the half-diameter of the terrestrial orbit''.<ref>{{cite journal
| first1      = Laurence
| last1       = Bobis
| first2      = James
| last2       = Lequeux
| title       = Cassini, Rømer and the velocity of light
| url         = https://articles.adsabs.harvard.edu/pdf/2008JAHH...11...97B
| journal     = J. Astron. Hist. Herit.
| volume      = 11
| issue       = 2
| pages       = 97–105
| date        = 2008
| doi = 10.3724/SP.J.1440-2807.2008.02.02
| bibcode     = 2008JAHH...11...97B
| s2cid = 115455540
}}</ref></blockquote>

[[File:Illustration from 1676 article on Ole Rømer's measurement of the speed of light.png|thumb|Illustration from the 1676 article on Rømer's [[Speed of light#Astronomical measurements|measurement of the speed of light]]. Rømer compared the duration of Io's orbits as Earth moved towards Jupiter (F to G) and as Earth moved away from Jupiter (L to K).]]
Oddly, Cassini seems to have abandoned this reasoning, which Rømer adopted and set about buttressing in an irrefutable manner, using a selected number of observations performed by Picard and himself between 1671 and 1677. Rømer presented his results to the [[French Academy of Sciences]], and it was summarised soon after by an anonymous reporter in a short paper, ''{{lang|fr|Démonstration touchant le mouvement de la lumière trouvé par M. Roemer de l'Académie des sciences}}'', published 7 December 1676 in the ''[[Journal des sçavans]]''.<ref>{{cite journal |last1=Romer |title=Démonstration touchant le mouvement de la lumière trouvé par M. Roemer de l'Académie des sciences |journal=Le Journal des Sçavans |date=1676 |pages=233–236 |url=https://gallica.bnf.fr/ark:/12148/bpt6k56527v/f234.image |trans-title=Demonstration concerning the movement of light found by Mr. Romer of the Academy of Sciences |language=fr}}</ref> Unfortunately, the reporter, possibly in order to hide his lack of understanding, resorted to cryptic phrasing, obfuscating Rømer's reasoning in the process. Rømer himself never published his results.<ref name="Teuber218">{{cite book
| last            = Teuber
| first           = Jan
| display-editors = 4
| editor          = Friedrichsen, Per
| editor2         = Henningsen, Ole
| editor3         = Olsen, Olaf
| editor4         = Thykier, Claus
| editor5         = Tortzen, Chr. Gorm
| title           = Ole Rømer&nbsp;– videnskabsmand og samfundstjener
| date            = 2004
| publisher       = Gads Forlag
| location        = Copenhagen
| language        = da
| isbn            = 87-12-04139-4
| page            = 218
| chapter         = Ole Rømer og den bevægede Jord&nbsp;– en dansk førsteplads?
}}</ref>

Rømer's reasoning was as follows. Referring to the illustration, assume the Earth is at point ''L'', and Io emerges from Jupiter's shadow at point ''D''. After several orbits of Io, at 42.5 hours per orbit, the Earth is at point ''K''. If light is not propagated instantaneously, the additional time it takes to reach ''K'', which he reckoned about 3½ minutes, would explain the observed delay. Rømer observed ''immersions'' at point ''C'' from positions ''F'' and ''G'', to avoid confusion with [[eclipse]]s (Io shadowed by Jupiter from ''C'' to ''D'') and [[occultation]]s (Io hidden behind Jupiter at various angles). In the table below, his observations in 1676, including the one on 7 August, believed to be at the opposition point ''H'',<ref>Point ''H'' had occurred about one month earlier, according to {{cite web
 |url          = http://math-ed.com/Resources/GIS/Geometry_In_Space/java1/Temp/TLVisPOrbit.html
 |title        = Visualize Solar System at a given Epoch
 |access-date  = 9 March 2009
 |author       = Dieter Egger
 |date         = 24 February 1997
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20090322002132/http://math-ed.com/Resources/GIS/Geometry_In_Space/java1/Temp/TLVisPOrbit.html
 |archive-date = 22 March 2009
 }}</ref> and the one observed at [[Paris Observatory]] to be 10 minutes late, on 9 November.<ref name="Saito">{{cite journal
| last    = Saito
| first   = Yoshio
| title   = A Discussion of Roemer's Discovery concerning the Speed of Light
| journal = AAPPS Bulletin
| volume  = 15
| issue   = 3
| pages   = 9–17
| date    = June 2005
}}</ref>

{| class="wikitable" style="text-align:right; margin:1em auto 1em auto;"
|+ The eclipses of Io recorded by Rømer in 1676<br /><span style="font-weight:500; font-size:80%; line-height:80%;">Time is normalized (hours since midnight rather than since noon); values on even rows are calculated from the original data.</span>
|-
! Month
! Day
! Time
! Tide
! orbits
! average (hours)
|-
| May
| 12
| 2:49:42
| '''C'''
| colspan="2" | 
|-
| colspan="3" | <small>2,837,189s</small>
|
| 18
| 41.48
|-
| June
| 13
| 22:56:11
| '''C'''
| colspan="2" | 
|-
| colspan="3" | <small>4,748,019s</small>
|
| 31
| 42.54
|-
| Aug
|  7
| 21:49:50
| '''D'''
| colspan="2" | 
|-
| colspan="3" | <small>611,765s</small>
|
| 4
| 42.48
|-
| Aug
| 14
| 23:45:55
| '''D'''
| colspan="2" | 
|-
| colspan="3" | <small>764,718s</small>
|
| 5
| 42.48
|-
| Aug
| 23
| 20:11:13
| '''D'''
| colspan="2" | 
|-
| colspan="3" | <small>6,729,872s</small>
|
| 44
| 42.49
|-
| Nov
|  9
| 17:35:45
| '''D'''
| colspan="2" | 
|}

By [[trial and error]], during eight years of observations Rømer worked out how to account for ''the retardation of light'' when reckoning the [[ephemeris]] of Io. He calculated the delay as a proportion of the angle corresponding to a given Earth's position with respect to Jupiter, ''Δt''&nbsp;=&nbsp;22·({{frac|α|180°}})<nowiki>[minutes]</nowiki>. When the angle α is 180° the delay becomes 22 minutes, which may be interpreted as the time necessary for the light to cross a distance equal to the diameter of the Earth's orbit, '''H''' to '''E'''.<ref name="Saito" /> (Actually, Jupiter is not visible from the conjunction point '''E'''.) That interpretation makes it possible to calculate the strict result of Rømer's observations: The ratio of the speed of light to the speed with which Earth orbits the sun, which is the ratio of
the duration of a year divided by pi as compared to the 22 minutes

{{frac|365·24·60|''π''·22}} ≈ 7,600.

In comparison, the modern value is circa {{frac|299,792&nbsp;km&nbsp;s<sup>−1</sup>|29.8&nbsp;km&nbsp;s<sup>−1</sup>}} ≈ 10,100.<ref>{{cite book
| last      = Knudsen
| first     = Jens Martin
| author2   = Hjorth, Poul G.
| title     = Elements of Newtonian Mechanics
| orig-year  = 1995
| edition   = 2nd
| date      = 1996
| publisher = Springer Verlag
| location  = Berlin
| isbn      = 3-540-60841-9
| page      = 367
}}</ref>

Rømer neither calculated this ratio, nor did he give a value for the speed of light. However, many others calculated a speed from his data, the first being [[Christiaan Huygens]]; after corresponding with Rømer and eliciting more data, Huygens deduced that light travelled {{frac|16|2|3}} Earth diameters per second,<ref>[[Christiaan Huygens|Huygens, Christiaan]] (8 January 1690) ''[http://www.gutenberg.org/catalog/world/readfile?fk_files=164378 Treatise on Light]''. Translated into English by Silvanus P. Thompson, [[Project Gutenberg]] etext, [http://www.gutenberg.org/catalog/world/readfile?fk_files=164378&pageno=11 p. 11]. Retrieved on 29 April 2007.</ref> which is approximately 212,000&nbsp;km/s.

Rømer's view that the velocity of light was finite was not fully accepted until measurements of the so-called [[aberration of light]] were made by [[James Bradley]] in 1727.

In 1809, again making use of observations of Io, but this time with the benefit of more than a century of increasingly precise observations, the astronomer [[Jean Baptiste Joseph Delambre]] reported the time for light to travel from the Sun to the Earth as 8 minutes and 12 seconds. Depending on the value assumed for the astronomical unit, this yields the speed of light as just a little more than 300,000 kilometres per second. The modern value is 8 minutes and 19 seconds, and a speed of 299,792.458&nbsp;km/s.

A plaque at the Observatory of Paris, where the Danish astronomer happened to be working, commemorates what was, in effect, the first measurement of a universal quantity made on this planet.

== Inventions ==
In addition to inventing the first street lights in Copenhagen,<ref>{{cite book
| title     = Litteraturens Perioder
| url       = https://books.google.com/books?id=f2A8q_o9FLMC&pg=PA27
| date      = 2005
| publisher = Gyldendal Uddannelse
| language  = da
| isbn      = 978-87-02-01832-5
| pages     = 27–
| quote     = En af deltagerne i enevældens storstilede forsøg på at skabe orden var Ole Rømer, der ikke blot var ... og i en periode borgmester i København, hvor han bl.a. fik skabt et effektivt brandvæsen og en ordentlig gadebelysning.
}}</ref><ref name="Rying1974">{{cite book
| author    = Bent Rying
| title     = Denmark: An Official Handbook
| url       = https://books.google.com/books?id=FAtpAAAAMAAJ
| date      = 1974
| publisher = Press and Cultural Relations Department, Royal Danish Ministry of Foreign Affairs
| pages     = 661–
| isbn = 9788785112187
| quote     = About the year 1700, the astronomer Ole Romer (1644–1710) displayed considerable technical activities as a public official ... knowledge to improving Danish streets and roads, harbours and bridges, water supplies, street lighting, and sewers.
}}</ref> Rømer also invented the [[meridian circle]],<ref>{{cite book
| title     = Meddelelser fra Ole Rømer-observatoriet i Aarhus
| url       = https://books.google.com/books?id=qR4aAQAAMAAJ
| date      = 1958
| publisher = Observatoriet
| pages     = 177–
| quote     = This extract from Ramus's thesis, together with his plate, shows clearly that Romer's Rota Meridiana was a meridian circle, taking this term in its modern meaning. The meridian circle was the final step in his series of instruments, in which ...
}}</ref><ref name="Altena2012">{{cite book
| author    = William F. van Altena
| title     = Astrometry for Astrophysics: Methods, Models, and Applications
| url       = https://books.google.com/books?id=sSvYOY2liHkC&pg=PA299
| date      = 22 November 2012
| publisher = Cambridge University Press
| isbn      = 978-0-521-51920-5
| pages     = 299–
| quote     = The pursuit of better accuracy led Ole Romer to develop the meridian circle in 1690 which, with modifications, is still in use today. The meridian circle or transit circle (conceived at the end of the seventeenth century) was a combination of a ...
}}</ref><ref name="English2010">{{cite book
| author    = Neil English
| title     = Choosing and Using a Refracting Telescope
| url       = https://books.google.com/books?id=fOXuIG1UDwEC&pg=PA6
| date      = 28 September 2010
| publisher = Springer Science & Business Media
| isbn      = 978-1-4419-6403-8
| pages     = 6–
| quote     = With a similar telescope, the Danish astronomer Ole Romer, witnessing a timing glitch in the eclipse of a Jovian satellite, ... Romer is also credited for inventing the meridian transit circle telescope (usually just called the meridian circle), ...
}}</ref> the [[altazimuth mount|altazimuth]],<ref name="ColbySandeman1913">{{cite book
| author1   = Frank Moore Colby
| author2   = George Sandeman
| title     = Nelson's Encyclopaedia: Everybody's Book of Reference ...
| url       = https://books.google.com/books?id=VjZAAAAAYAAJ
| date      = 1913
| publisher = Thomas Nelson
| pages     = 193–
| quote     = The altazimuth (invented by Olaus Romer of Copenhagen in 1690) is available for measurements in all parts of the sky; and it was with a combination of this type, completed by Ramsden in 1789, that Piazzi made the observations for his great ...
}}</ref><ref name="Chrisholm1911">{{cite EB1911|wstitle= Astronomy |volume= 2 | | pages = 800&ndash;819; see page 814 |quote= "Cassini, moreover, set up an altazimuth in 1678, and employed from about 1682 a "parallactic machine," provided with clockwork to enable it to follow the diurnal motion. Both inventions have been ascribed to Olaus Römer, who used but did not claim them....." |last1= Clerke |first1= Agnes Mary |author-link= Agnes Mary Clerke}}
</ref> and the passage instrument (also known as the ''transit instrument'', a type of meridian circle whose horizontal axis is not fixed in the east-west direction).<ref name="Schoppe2012">{{cite book
| author    = Siegfried Schoppe
| title     = Heinrich der Seefahrer, Kolumbus und Magellan: Planung, Versuch und Irrtum bei der Entdeckung der Neuen Welt durch Portugal und Spanien vor 500 Jahren
| url       = https://books.google.com/books?id=rMdtbPwPWfgC&pg=PA271
| date      = 2012
| publisher = BoD&nbsp;– Books on Demand
| language  = de
| isbn      = 978-3-8482-0910-1
| pages     = 271–
| quote     = Der dänische Astronom Ole Römer (1644&nbsp;– 1710) misst am Pariser Observatorium die Lichtgeschwindigkeit mit ... Das "Passage-Instrument" setzt sich nicht durch, weil es für die Kapitäne zu kompliziert und nur bei klarer Sicht und ganz ...
}}</ref><ref name="Congres1927">{{cite book
| author   = Nederlands Natuur- en Geneeskundig Congres
| title    = Handelingen
| url      = https://books.google.com/books?id=4yMWAQAAIAAJ
| volume   = 21-22
| date     = 1927
| language = nl
| pages    = 70–
| quote    = ... slingeruurwerk van Huygens veranderde de zaak echter, en nu kon Ole Römer, de geniale Deensche astronoom, in 1689 een passage-instrument construeeren, dat in 1704 omgebouwd werd.
}}</ref>

== Ole Rømer Medal ==
The {{Interlanguage link|Ole Rømer Medal|da|3=Ole Rømer-medaljen}} is given annually by the Danish Natural Science Research Council for outstanding research.<ref>[http://universitetsavisen.ku.dk/dokument2/dokument2/dokument7/Uni10.01.pdf/ Med eksprestog til evigheden] universitetsavisen.ku.dk {{Webarchive|url=https://web.archive.org/web/20160322070852/http://universitetsavisen.ku.dk/dokument2/dokument2/dokument7/Uni10.01.pdf/ |date=22 March 2016 }}</ref>

== The Ole Rømer Museum ==
The Ole Rømer Museum is located in the municipality of [[Høje-Taastrup]], Denmark,<ref name="RigdenStuewer2009">{{cite book
| author1   = John S. Rigden
| author2   = Roger H Stuewer
| title     = The Physical Tourist: A Science Guide for the Traveler
| url       = https://books.google.com/books?id=i4uLnMZeACsC&pg=PA62
| date      = 29 May 2009
| publisher = Springer Science & Business Media
| isbn      = 978-3-7643-8933-8
| pages     = 62–
| quote     = Danish astronomer Ole Rømer (1644–1710) studied at the University of Copenhagen. ... from his home in Kannikestræde and at a new observatory built to the west of Copenhagen, now the site of the Ole Rømer Museum
}}</ref> at the excavated site of Rømer's observatory ''{{Interlanguage link|Observatorium Tusculanum|da}}'' at Vridsløsemagle.<ref>{{cite book
| title    = Nordisk universitets-tidskrift
| url      = https://books.google.com/books?id=V0UoAAAAMAAJ&pg=RA2-PA6
| date     = 1854
| language = da
| pages    = 6–
| quote    = ... den længe forhen af den Danske berömle Astronom Ole Römer forfærdigede Cirkel, hvilken han kaldte rota meridiana, ... Ophold paa hans saakaldte Observatorium Tusculanum i Landsbyen Wridslöse-Magte, nogle Mile fra Kjöbenhavn.
}}</ref><ref>{{cite book
| title     = Historiske meddelelser om København
| url       = https://books.google.com/books?id=Y5EbAQAAIAAJ
| date      = 1936
| publisher = Københavns Kommune.
| language  = da
| pages     = 316–
| quote     = Trods Observatoriets nu saa fortrinlige og moderne Indretning synes Rømer dog ikke at have været helt tilfreds med Forholdene. Det er, saa vidt det ... Hvis vi undersøger de fleste af vore borgerlige Indretningers Historie, vil vi støde paa Ole Rømers Navn. ... Hans Elever har sikkert ogsaa observeret baade her og i det andet private "Observatorium tusculanum", som han byggede sig i Vridsløsemagle.
}}</ref><ref name="PetersenAndersen1929-716">{{cite book
| author1   = Carl Sophus Petersen
| author2   = Vilhelm Andersen
| author3   = Richard Jakob Paulli
| title     = Illustreret dansk litteraturhistorie: bd. Den danske littterature fra folkevandringstiden indtil Holberg, af C.S. Petersen under medvirkning af R. Paulli
| url       = https://books.google.com/books?id=9MUSAAAAMAAJ
| date      = 1929
| publisher = Gyldendai
| language  = da
| pages     = 716–
| quote     = ... København og Roskilde, sit "Observatorium Tusculanum", som han med en klassisk Vending symbolsk kaldte det.
}}</ref> The observatory opened in 1704, and operated until about 1716, when the remaining instruments were moved to Rundetårn in Copenhagen.<ref>{{cite book
| title     = København
| url       = https://books.google.com/books?id=1IPeH4SWiBYC&pg=PA133
| date      = 2004
| publisher = Gyldendal A/S
| language  = da
| isbn      = 978-87-02-03645-9
| pages     = 133–
| quote     = Allerede Ole Rømer ( 1644–1710 ) var mere ambitiøs. Han syntes, der var alt for meget lys og røg i byen til, at man kunne se ordentligt, så han byggede sit eget observatorium i Vridsløsemagle langt uden for København.
}}</ref> There is a large collection of ancient and more recent astronomical instruments on display at the museum.<ref>{{cite book
| title     = Skalk, nyt om gammelt
| url       = https://books.google.com/books?id=nuEiAQAAIAAJ
| date      = 1999
| publisher = Forhistorisk Museum
| language  = da
| pages     = xiv–
}}</ref> The museum opened in 1979, and has since 2002 been a part of the museum [[Kroppedal]] at the same location.<ref>{{cite book
| title     = Historisk tidsskrift
| url       = https://books.google.com/books?id=fx4WAQAAMAAJ
| volume    = 106
| date      = 2006
| publisher = Den Danske Forening
| language  = da
| pages     = 743–
| quote     = Det var astronomen Claus Thykier, der havde fået den idé, at han ville finde det sted, hvor Ole Rømer (1644–1710) i 1704 ... I 1979 kunne Ole Rømer Museet åbne i lokaler på gården Kroppedal få hundrede meter fra fundstedet med Claus ...
}}</ref><ref>{{cite web
| url        = http://www.denstoredanske.dk/Kunst_og_kultur/Museumsv%C3%A6sen/Generelt/Kroppedal
| title        = Kroppedal &#124; Gyldendal&nbsp;– Den Store Danske
| publisher        = Denstoredanske.dk
| access-date        = 5 October 2015
| archive-url        = https://web.archive.org/web/20151006103616/http://www.denstoredanske.dk/Kunst_og_kultur/Museumsv%C3%A6sen/Generelt/Kroppedal
| archive-date        = 6 October 2015
| url-status        = dead
}}</ref><ref>{{cite news
| author     = Camilla Stockmann
| url        = http://politiken.dk/kultur/kunst/ECE2462784/tycho-brahe-maleri-er-forsvundet/
| title      = Tycho Brahe-maleri er forsvundet
| language   = da
| publisher  = Politiken.dk
| date       = 23 November 2014
| access-date = 5 October 2015
}}</ref>

== Honours ==
In Denmark, Ole Rømer has been honoured in various ways through the ages. He has been portrayed on bank notes,<ref name="JensenScocozza1996">{{cite book
| author1   = Grethe Jensen
| author2   = Benito Scocozza
| title     = Politikens bog om danskerne og verden: hvem, hvad, hvornår i 50 år
| url       = https://books.google.com/books?id=epIlAQAAMAAJ
| date      = 1996
| publisher = Politikens forlag
| language  = da
| isbn      = 978-87-567-5697-6
| pages     = 253–
}}</ref> the eponymous {{Interlanguage link|Ole Rømer's Hill|da|3=Ole Rømers Høj}} is named after him,<ref name="Lidegaard1998">{{cite book
| author    = Mads Lidegaard
| title     = Danske høje fra sagn og tro
| url       = https://books.google.com/books?id=6NHYAAAAMAAJ
| date      = 1 January 1998
| publisher = Busck
| language  = da
| isbn      = 978-87-17-06754-7
| pages     = 86–
| quote     = Ole Rømers Høj (oprindelig Kongehøj) er den største høj i hele området, 6&nbsp;m høj med stejle sider og en hel flad top. Den menes bygget i jernalderens sidste århundreder eller vikingetiden og ligger lige øst for Vridsløsemagle syd for ...
}}</ref> as are streets in both Aarhus and Copenhagen (''Ole Rømers Gade'' and ''{{Interlanguage link|Rømersgade|da}}'' respectively).<ref>{{cite web
 |url          = http://gis.aarhus.dk/kommuneatlas/gadebeskrivelser/Gade_Ole_Roemers_Gade.htm
 |title        = Untitled Document
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20070731052636/http://gis.aarhus.dk/kommuneatlas/gadebeskrivelser/Gade_Ole_Roemers_Gade.htm
 |archive-date = 31 July 2007
 |access-date  = 5 October 2015
 }}</ref><ref name="Zinglersen1972">{{cite book
| author    = Bent Zinglersen
| title     = Københavnske gadenavne og deres historie
| url       = https://books.google.com/books?id=x38lAQAAMAAJ
| date      = 1972
| publisher = Politiken
| language  = da
| isbn      = 978-87-567-1651-2
| pages     = 185–
}}</ref> Aarhus University's astronomical observatory is named [[Science Museums, Aarhus#Ole Rømer Observatory|The Ole Rømer Observatory]] (''{{Interlanguage link|Ole Rømer Observatoriet|da}}'') in his honour, and a Danish satellite project to measure the age, temperature, physical and chemical conditions of selected stars, was named {{Interlanguage link|The Rømer Satellite|da|3=Rømer-satellitten}}. The satellite project stranded in 2002 and was never realised though.<ref>{{cite web
 |url          = http://astro.phys.au.dk/~jcd/MONS/english/Roemer/
 |title        = The Roemer satellite
 |publisher    = Astro.phys.au.dk
 |date         = 14 February 2001
 |access-date  = 5 October 2015
 |archive-url  = https://web.archive.org/web/20160304224955/http://astro.phys.au.dk/~jcd/MONS/english/Roemer/
 |archive-date = 4 March 2016
 |url-status   = dead
 }}</ref><ref>{{cite news
| url        = http://jyllands-posten.dk/aarhus/ECE4453229/satellit-fra-arhus-i-rummet-i-2003/
| title      = Satellit fra Århus i rummet i 2003 – Aarhus
| language   = da
| publisher  = Jyllands-posten.dk
| access-date = 5 October 2015
}}{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

The [[Römer (crater)|Römer crater]] on the Moon is named after him.<ref name="Zamarovský2013">{{cite book
| author    = Peter Zamarovský
| title     = Why is it dark at night?: Story of dark night sky paradox
| url       = https://books.google.com/books?id=JRYiAgAAQBAJ&pg=PA157
| date      = 18 November 2013
| publisher = AuthorHouse
| isbn      = 978-1-4918-7881-1
| pages     = 157–
| quote     = ... the homeless and prostitutes. In 1705 he became mayor of Copenhagen and a year later, Chairman of the Danish State Council. He died shortly before his sixtieth birthday. The Römer Crater is located in the north-east section of the Moon.
}}</ref>

=== In popular culture ===
In the 1960s, the comic-book superhero [[Flash (DC Comics character)|The Flash]] on a number of occasions would measure his velocity in "Roemers" {{sic}}, in honour of Ole Rømer's "discovery" of the [[speed of light]].<ref>{{cite web
| url   = http://rebuildingcivilization.blogspot.dk/2013/10/the-ultimate-time-machine-1-cosmic.html
| title   = Rebuilding Civilization: The Ultimate Time Machine 1: The Cosmic Treadmill
| work   = rebuildingcivilization.blogspot.dk
| access-date   = 5 October 2015
| archive-url   = https://web.archive.org/web/20151006031334/http://rebuildingcivilization.blogspot.dk/2013/10/the-ultimate-time-machine-1-cosmic.html
| archive-date   = 6 October 2015
| url-status   = dead
}}</ref>{{Better source needed|date=October 2015}}

In [[Larry Niven]]'s 1999 novel ''[[Rainbow Mars]]'', Ole Rømer is mentioned as having observed [[Martian]] life in an [[alternate history]] timeline.

Ole Rømer features in the 2012 game ''[[Empire: Total War]]'' as a gentleman under Denmark.

On 7 December 2016, a [[Google Doodle]] was dedicated to Rømer.<ref>{{cite web
| url   = https://doodles.google/doodle/340th-anniversary-of-the-determination-of-the-speed-of-light/
| title = 340th anniversary of the determination of the speed of light.
}}</ref>

== Notes and references ==
{{Reflist|30em}}

== Sources ==
* {{cite journal
| last1    = MacKay
| first1   = R. Jock
| last2   = Oldford
| first2  = R. Wayne
| date    = 2000
| title   = Scientific Method, Statistical Method and the Speed of Light
| url     = https://www.researchgate.net/publication/38326843
| journal = Statistical Science
| volume  = 15
| issue   = 3
| pages   = 254–278
| doi     = 10.1214/ss/1009212817
| doi-access= free
}} {{Small|(Mostly about [[Albert Abraham Michelson|A.A. Michelson]], but considers forerunners including Rømer.)}}
* {{cite book
| author1   = Axel V. Nielsen
| title     = Ole Romer, en Skildring af hans Liv og Gerning
| url       = https://books.google.com/books?id=uvA0AQAAIAAJ
| date      = 1944
| publisher = Nordisk Forlag
| language  = da
}}

== External links ==
{{Commons category-inline|Ole Rømer}}
* [http://galileo.rice.edu/Catalog/NewFiles/roemer.html Roemer, Ole Christensen] ''(at the [http://galileo.rice.edu/ Galileo Project])''
* [https://cral-perso.univ-lyon1.fr/labo/fc/ama09/pages_jdsc/pages/jdsc_1676_lumiere.pdf ''Démonstration touchant le mouvement de la lumière''] ''(The 1676 paper on the speed of light, in old French, as ordinary text)''
* [https://web.archive.org/web/20040603113143/http://www.rundetaarn.dk/engelsk/observatorium/light.htm Rømer and the Doppler Principle.] ''(further details on Rømer's result)''
* {{in lang|da}} [https://web.archive.org/web/20030416231847/http://www.rundetaarn.dk/dansk/observatorium/indledning.htm ''Fysikeren Ole Rømer''] ''(in Danish)''
* [http://www.kroppedal.dk/ ''Kroppedal Museum'']
* [http://www-personal.umich.edu/~jbourj/money4.htm Ole Rømer on the 50 Danish Kroner banknote] {{Webarchive|url=https://web.archive.org/web/20180803223823/http://www-personal.umich.edu/~jbourj/money4.htm |date=3 August 2018 }}

{{Authority control}}

{{DEFAULTSORT:Romer, Ole}}
[[Category:1644 births]]
[[Category:1710 deaths]]
[[Category:18th-century Danish astronomers]]
[[Category:18th-century Danish letter writers]]
[[Category:17th-century Danish astronomers]]
[[Category:Creators of temperature scales]]
[[Category:Gregorian calendar]]
[[Category:Members of the French Academy of Sciences]]
[[Category:Members of the Prussian Academy of Sciences]]
[[Category:People from Aarhus]]
[[Category:Rectors of the University of Copenhagen]]
[[Category:Danish scientific instrument makers]]
[[Category:University of Copenhagen alumni]]
[[Category:Burials at the Church of Our Lady, Copenhagen]]