Ole Christensen Roemer (September 25, 1644 - September 19, 1710) was a Danish astronomer. In 1676, while working at the Royal Observatory in Paris, he made the first quantitative measurements of the speed of light. His determination of the speed of light demonstrated that light has a finite speed, and so doesn't travel instantaneously. In 1681, he was appointed professor of astronomy at the University of Copenhagen. As royal mathematician, he introduced the first national system for weights and measures in Denmark in 1683. He developed one of the first temperature scales. Fahrenheit visited him in 1708 and improved on the Roemer scale, the result being the familiar Fahrenheit temperature scale still in use today in a few countries. In 1705, he was made the second Chief of the Copenhagen Police, a position he kept until his death in 1710. 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. He 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. He also invented the meridian circle and the altazimuth. Roemer died in 1710 at the age of 65.