Remote patrol

"Nova" (7 tonight on Channel 19) tells an enchanting story behind a topic almost none of us today pays attention to: longitude. But when the seas were the key to a nation's power and prosperity, the wild inaccuracy of clocks made it impossible to sail a boat or draw a map with any certainty. Two hundred years before Charles Lindbergh won a prize for flying across the Atlantic, a "longitude prize" was offered to whoever could chart their way precisely across the ocean. Tonight's program, narrated by Richard Dreyfuss, re-creates the drama of that competition and how a village carpenter and clockmaker, John Harrison, and his superaccurate wooden timepiece challenged the scientists and the astronomers. Based on Dava Sobel's book, Longitude.