By Dava Sobel
Umberto Eco's "romance of navigation and science in the mid-seventeenth century" traces a tale of love and longing across two oceans at a time when the sea posed terrible perils to travelers. The story opens in 1643 at what turns out to be the "antipodal meridian," or the international date line, where Roberto finds himself shipwrecked on shipboard. Halfway around the world from the Paris meridian -- and at the furthest possible remove from his beloved lady -- he is a victim of the longitude problem. The longitude problem, or, as Eco more poetically terms it, "the mystery of the longitude," embroils Roberto in international espionage and launches him on his fateful voyage.
For want of a practical method of determining longitude, every great captain in the Age of Exploration became lost at sea despite his charts and compasses. From Vasco de Gama to Sir Francis Drake -- they all got where they were going willy-nilly, by forces attributed to good luck or the grace of God. Any sailor worth his salt could gauge his latitude well enough by the length of the day, or the height of the sun, or certain guide stars above the horizon. Longitude, in contrast, had to be measured by time.
As early as 1514, navigators well knew that the secret to determining longitude at sea lay in comparing the time aboard ship to the time at the home port -- at the very same moment. They could then convert the hour difference between the two places into a geographical one: Since the Earth takes twenty-four hours to complete one full revolution of three hundred sixty degrees, in one hour it completes one twenty-fourth of that, or fifteen degrees. Each hour's time difference between the ship and the starting point therefore marks a progress of fifteen degrees of longitude to the east or west. Unfortunately, although navigators could figure out their local time at sea by watching the sun every day to see when it reached its highest point in the sky (at noon), they could not keep track of time at another place. For that they would have needed a clock or watch set to the home port. But pendulum clocks went haywire on the decks of rolling ships: they slowed down, or sped up, or stopped running altogether. Pocket watches from that period fell far short of the accuracy required for navigation. Astronomers tried to give mariners a way to tell time in two places at once by the moon and stars. Indeed, the great observatories in Paris and London were founded (in 1666 and 1674, respectively) not to conduct pure research in astronomy, but to perfect the art of navigation.
Ignorance of longitude killed untold numbers of sailors whose destinations suddenly loomed out of the sea, taking them by surprise. In one such accident, on October 22, 1707, at the Scilly Isles near the southwestern tip of England, four homebound British warships ran aground and two thousand men drowned. Long voyages waxed longer for not knowing longitude, as a captain might search weeks for the island where he hoped to find fresh water, or even the continent that was his destination. Extra time at sea condemned sailors to the dread disease of scurvy, caused by a lack of vitamin C, and expressed as the fatal deterioration of their blood vessels.
Beyond this potential for human suffering, the longitude problem wreaked economic havoc on the grandest scale. It confined ocean traffic to a few narrow shipping lanes, where whaling ships, merchant ships, warships, and pirate ships all clustered and fell prey to one another. So insuperable was the challenge of finding longitude at sea that it consumed the greatest minds of the European scientific establishment, including Galileo Galilei. In fact, the brass helmet with attached spyglass that Roberto helps Father Caspar don aboard the Daphne was invented by Galileo in 1616 to help sailors use the moons of Jupiter as a heavenly clock.
No wonder the French court was so eager to steal longitude secrets from state enemies. Coerced by Cardinal Richelieu, Roberto sails aboard a Dutch ship to spy on a British scientist who, navigating unknown waters by the cries of a wounded dog, seems to have unlocked the secret of longitude.
Although this technique of navigation by canine vivisection may sound like the purest fiction, it was actually proposed as a solution in London in 1688 -- whether in desperation or in jest is not known. The anonymous author relied on the same Powder of Sympathy that dusts Eco's pages. This quack cure, brought to England from France by Sir Kenelm Digby, was a powder that could purportedly heal at a distance when applied to some article from an injured person. As Roberto learned at the siege of Casale and later during his sojourn in Paris, the treatment was not painless: Patients jumped or swooned when practitioners powdered the swords that had cut them or the cloths that had dressed their wounds.
To apply the Powder to the longitude problem, a wounded dog was to be put aboard a departing ship, and a trusted individual was left ashore to dip a bit of the dog's discarded bandage into Sympathy solution every day at a prearranged hour. The dog could be counted upon to yelp in pain at that instant, thereby announcing the crucial home-port time to the crew. Despite the wounded dog, however, and even a wounded human enslaved in the same service, The Island of the Day Before ends before the longitude problem meets with its solution.
In 1714, the British Parliament passed the famed Longitude Act, offering a handsome reward (the equivalent of several million dollar's in today's currency) for a solution. Many hopeful contenders competed for the longitude prize. Scientists perfected a workable astronomical technique by the middle of the eighteenth century, but it proved unwieldy and complicated. It fell by the wayside after John Harrison, a self-educated English clock maker, built an accurate sea clock that could carry the home-port time, like an eternal flame, to any remote corner of the world. Harrison, who devoted four decades of his life to this endeavor, finally succeeded in 1759 -- more than one hundred years too late to guide Roberto safely back into the arms of his faraway love.
Dava Sobel is the author of The New York Times bestseller Longitude. An award-winning former science reporter for The New York Times, she writes frequently about science for several magazines, including Audubon, Discover, Life, and The New Yorker.