Dec2004 update: I did eventually buy the DVD set, and it is very nice.
"Longitude" is a towering achievement as a movie. Shown in 4 hours on A&E network, I taped it to skip the commercials and was able to watch it in just over 3 hours. I only give ratings of "10" to truly remarkable movies, and this is one. It helps to be a scientist, and to have had a life-long fascination with navigation and timepieces.
The story is historical - the British government passed an act in the early 1700s for a prize of 20,000 Pounds for the first to provide an accurate and practical means of establishing longitude at sea. A Board of Longitude,comprising self-important scientists, would judge when the challenge was met.
John Harrison, a carpenter who understood the sun's apparent movement with the Earth's rotation, figured you could do it with a very accurate clock. He, with help from his son William, did it over a period of about 50 years, and met all conditions with his 4th clock, but the board kept throwing up roadblocks to avoid giving the award to someone who was not a scientist but a mere "carpenter." Finally, when Harrison was 80, in the year 1774, was given the prize by Parliament. He died only two years later.
The ancient story was interwoven with a WWII-era story of a man, played by Jeremy Irons, who undertook to restore all of Harrison's old clocks, and finally succeeded against similar resistance that Harrison had faced.
If you either are not a scientist, or do not appreciate the magnitude of Harrison's effort, and its contribution to modern navigation, then it is possible that you would find this movie somewhat boring. Do yourself a favor - don't waste your time. For me, it remains one of the absolute best movies I have ever seen, both in significance of the story and the mastery of the acting and direction.
