Latitude was easily measured using the position of the Sun or stars, but how did the sailors measure their longitude? It was a very difficult problem to solve. In 1714 a prize of 20,000 pounds (a lot of money in those days!) was offered to anyone who could provide an accurate way to measure longitude at sea.
 A very clever watchmaker called John Harrison eventually won the prize by making a clock which kept accurate time, even in stormy weather. With this clock, the sailors were able to keep track of the time at the place the ship sailed from. The difference between that clock time and the 'local noon' (when the Sun is highest in the sky) could be used to calculate their longitude.
John Harrison and his timekeeper. |
