This instalment of NOVA follows the search for the key to navigating the seas. It is based on the best selling book Longitude by Dava Sobel.
Lost at Sea: The Search for Longitude, begins with the story of Will Andrewes, as he joins a crew to try out and replicate a typical log and line method of the early 1700s to determine the speed and course of a sailing ship.
It was a crude method, using a triangle of wood(called a log) with a knotted line tied to it. They would count the number of knots that passed through the navigator's fingers in the time it took a 28-second sand glass to flow through. This would give the speed of the ship in knots and was the only way to tell the distance a ship traveled at sea.
This method is outlined step by step at the Navigating the Ocean website.
|Harrison's "Sea Watch" No.1 (H4), with winding crank|
These ideas were advanced by astronomers and by accurate timepieces made by John Harrison in the 1700s. The rest of the episode shows the continued quest for the accurate determination of longitude through astronomy and accurate time keeping at sea.
Lost at Sea - The Search for Longitude is available on DVD through Amazon.com.
Additional education material associated with this episode of NOVA is available at PBS online.
NOVA: Lost At Sea - The Search For Longitude (1998)