National Geographic : 1970 Jun
Albert Bumstead's backward sundial saw Byrd safely home It was May 9, 1926. Three thou sand feet above bleak polar ice stretching featureless to the horizon, Lt. Comdr. Richard Evelyn Byrd and his pilot, Floyd Bennett, gazed with nearly equal fascination at two things-the North Pole below them, and the oil leaking from one of their airplane's three straining engines. Now they belonged to history, the first men to fly to the North Pole. It remained for them to return safely to their base over the endless frozen ocean. The pioneers pointed the nose of the Josephine Ford toward their base in Spitsbergen, nearly 700 miles away. Suddenly, their sextant slid from the chart board and crashed to the deck of the plane, broken. At the top of the world, where their magnetic compass was useless, where there were no charts and no land marks, their lives now depended on the accuracy of one instrument, the Bumstead Sun Compass. , Simple in principle, as are many great inventions, and ingenious in operation, the sun compass was invented and built by National Geographic Society's first Chief Cartographer, Albert H. Bumstead. It was a remark able answer to the unique prob lems of polar navigation which the Byrd Expedition faced. Since during the polar sum mer the sun never goes below the horizon, the Bumstead com pass was made to be a kind of sundial in reverse. A sundial, accurately adjusted according to its position on earth, will, by the sun's shadow, tell time. Conversely, the Bum stead compass, with the time already known, makes use of the sun's shadow to tell position. The Bumstead compass is basically an accurate 24-hour clock, or chronometer, with a single hand, or pointer. To use it, the clock is set carefully to local sun time, the clock face is tipped to the approximate latitude of the area by means of the latitude quadrant, and the whole instrument turned so that the hour hand points directly to the sun. By keeping the hour hand steadily toward the sun, with the shadow of the vertical pin centered along it, the 12 o'clock mark on the dial will point south. Navigating more than five hours with the sun compass alone, the two polar explorers raised their base dead ahead on the horizon and made a safe, triumphant landing. In 1929, the same sun com pass, with its mechanism ad justed for southern polarity, guided Byrd on his epic flight over the towering 10,000-foot South Polar plateau. And it was with him on his last flight to the South Pole in 1956, a dependable check on the more complex instruments of a new generation of flight. Retired now, the Bumstead Sun Compass rests in the Society's Explorers Hall in the Nation's Capital, with other exhibits of the great age of polar exploration. That age may be over, but readers continue to explore new frontiers of the world, of space, and of science each month in the pages of NATIONAL E GEOGRAPHIC.