This excellent video from the NOVA series is based on the book Longitude by Dava Sobel. It takes you aboard an authentic tall ship and back in time to see history in the making. Not only does this video portray the story of John Harrison’s 58 year effort to solve the problem of longitude with his accurate clock, but it depicts and explains much of the background of navigational methods of the 1700s. It explains the system of latitude and longitude as a means of geographical location. Use of the cross staff for finding latitude, finding speed with a log, and telling time astromonically by lunar distances and Jovian moon positions in order to obtain longitude are all shown and discussed. 60 min. SW 1 lb.