It's hard for us to imagine today, with watches so cheap they're given away with Happy Meals and handheld GPS units that tell us our precise location on Earth, but there was a time when neither time nor place could be determined with absolute certainty. With no reliable way of determining longitude -- or east/west location -- countless sailing ships and their crews were doomed to horrible deaths when miscalculations crashed them on rocky shoals or failed to alert them that land with fresh food and water was lurking just over the horizon. So, in the early 18th century, Britain's Queen Anne announced a £20,000 prize -- truly a royal sum in those days -- to anyone who could devise a "practicable and useful" solution to the "problem of the longitude," with a Board of Longitude to adjudicate. Lives and ships were not the only thing at stake -- mastery over longitude would also assure Britain's military and commercial mastery of the seas.

A&E's Longitude -- directed by Charles Sturridge (Fairy Tale: A True Story), who also adapted Dava Sobel's extraordinary book of the same name -- is the story of rural clockmaker and carpenter John Harrison (Michael Gambon: Sleepy Hollow, The Insider), who decided that the solution to the longitude lay in time... and of British naval officer Rupert Gould (Jeremy Irons: The Man In The Iron Mask, Lolita), who, two hundred years after Harrison worked, strove to save Harrison's work from the ravages of time.

Longitude is time -- one degree of longitude corresponds to 8 minutes of the 24-hour day -- and Harrison saw that extremely precise timekeepers, ones that could maintain their accuracy at sea, would satisfy the requirements of the queen's act and win the prize. Such clocks were unknown in Harrison's day, however -- clocks ran on pendulums, and a ship's motion would throw a pendulum out of whack, amongst other technical problems. Harrison was undeterred, and devoted his life to building a series of more and more advanced clocks that solved puzzles that had vexed clockmakers for centuries.

Much of Longitude is devoted to the decades Harrison -- and later his son and apprentice, William (Ian Hart: The End Of The Affair, Monument Avenue) -- spent navigating the politics of the Board of Longitude. An unsophisticated "country toolmaker," in the words of one Board member, amongst bewigged city types, Harrison was constantly afraid of others stealing his ideas, and continually thwarted by the Board, which, comprised mostly of astronomers, was convinced the longitude problem would be solved by celestial clockwork, not the down-to-earth mechanical kind.

What gives Longitude so much depth and heft is Gould's story, so wonderfully intercut with Harrison's that a pan of the camera takes us from Harrison, stalking out of a hallowed hall after a frustrating meeting with the Board, to Gould, wandering the same building two centuries later in his quest to find Harrison's historic timepieces. So captivated by Harrison's work that it costs him his marriage, Gould, once he locates the broken and neglected "sea clocks," volunteers to clean and restore them on his own time, for no pay... just as Harrison worked to build them in the first place. Gould narrates, explaining the importance and uniqueness of each clock as he cleans and Harrison builds, and we see two men in simpatico, in love with time, in love with these marvelous machines.

And they are beautiful and odd and mysteriously startling, the early ones Rube Goldberg-esque devices that clank and clatter hypnotically, the last one like a giant's pocketwatch. Gould, as he hosts a children's radio science show, describes, in Irons's dulcet, warm-syrup voice, how clocks must have seemed like witchcraft, and Longitude does a terrific job of conveying the magic of Harrison's clocks. The love the clocks -- and the whole idea of timekeeping -- inspire in Harrison and Gould goes mostly uncommented upon, except that Gambon and Irons exude it, their performances exquisitely masterful, like the tiny precision works of Harrison's final watchlike clock, all their devotion and passion revealed on their faces through tiny quirks. And as William, Hart lets his wonderful face -- which should be weaselly but instead seems perpetually wounded and sorrowful -- do the job as well, showing us a man who is devoted not so much to the clocks as he is to his father.

From the Harrisons and Gould to the "longitude lunatics" the prize money draws, Longitude proves that history becomes fascinating when it isn't just about things or ideas or events but also about the people who were behind it all. It's those people -- and the remarkable cast portraying them -- who make Longitude so rewarding and actually fun.