QUOTE : The first experimental determination that the speed of light was not infinite was made by the seventeenth-century Danish astronomer, Ole Romer. In 1676, Romer was attempting to solve one of the great scientific and engineering challenges of the age; telling the time at sea. Finding an accurate clock was essential to enable sailors to navigate safely across the oceans, but mechanical clocks based on pendulums or springs were not good at being bounced around on the ocean waves and soon drifted out of sync. In order to pinpoint your position on Earth you need the latitude and longitude. Latitude is easy; in the Northern Hemisphere, the angle of the North Star (Polaris) above the horizon is your latitude. In the Southern Hemisphere, things are more complicated because there is no star directly over the South Pole, but it is still possible with a little astronomical know-how and trigonometry to determine your latitude with sufficient accuracy for safe navigation.