1676 demonstration of light's finite speed by Danish astronomer Ole Rømer In 1676, the Danish astronomer Ole Rømer demonstrated that light has a measurable speed and so does not travel instantaneously. Rømer was working at the Royal Observatory in Paris at the time. 869,465 views on December 7, 2016 — Wikipedia's most-read article that day. Also most read: HTTP 404, Junaid Jamshed, Nicaraguan Sign Language, J. Jayalalithaa. Wiki link