HISTORY OF SCIENCE AND TECHNOLOGY

OLE ROEMER (1644 - 1710)

Ole Roemer was born in Aarhus, Denmark in 1644. After attending Aarhus Cathedral School, he entered Copenhagen University in 1662. It was here that he met Erasmus Bartholinus (also known as Rasmus Bartholin) who was a professor of geometry and medicine at the university. Bartholinus discovered polarized light in 1669 through his observations on a mineral called calcite. Roemer worked with Bartholinus to edit some of Tycho Brahe’s manuscripts.

Roemer also met Jean Picard, the French astronomer who had been the first to measure the size of the Earth with reasonable accuracy. In 1671 the three scientists paid a visit to the Island of Hveen to locate Tycho Brahe’s observatory. In the following year, Roemer and Picard traveled to Paris. Roemer was well received in Paris; he lived in an apartment at the Paris Observatory and, for a while, he tutored the future Louis XV in astronomy. He remained in France for nine years and was elected to the Académie des Science. During his time in France he helped construct the fountains in Versailles.

The Director of the Académie in 1672 was Giovanni Cassini. Cassini’s work on the movement of Jupiter’s moons was used by Roemer in 1675 to help him calculate the speed of light. Until this time it was believed that light travelled instantaneously. Roemer proved that light had a finite velocity and his value for the speed of light was 220,000 km/sec. This figure is about 25% less than the actual speed of light, which is 299,792.458 km/sec, but it must be remembered that the instruments Roemer used were not anywhere near as accurate as those we use today.

In 1679 Roemer journeyed to England to take a look at a pendulum being made at the Royal Academy. While there he met Newton and Halley. In 1681 the King of Denmark, Christian V, recalled Roemer to Copenhagen and appointed him Royal Astronomer and Professor of Mathematics at Copenhagen University. Roemer was also famous for designing measuring instruments for use in engineering, hydraulics and cartography. He was responsible designing the layout of Copenhagen as the city expanded. This included planning the water supply and sewers, modernizing the fire department and setting out the cities pavements and squares. Roemer is also credited with developing the metric system of weights and measures and, in collaboration with Daniel Fahrenheit, he developed what was to become the Fahrenheit temperature scale.

In 1704 Roemer built, and paid for, his own observatory at Vridlosemagle, near Copenhagen, on land owned by Erasmus Bartholinus. He was made Mayor of Copenhagen in 1705 and Head of the Danish Council of State in 1706.

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