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In settlement, Pope Alexander VI issued the Bull of Demarcation. With aloof equanimity, His Holiness drew a meridian line from north to south on a chart of the great ocean, one hundred leagues west of the Azores. He assigned all lands west of the line, discovered or undiscovered, to Spain, and all lands to the east to Portugal. It was masterful diplomacy, particularly when no one knew where the line fell.
As a child, I learned the trick for remembering the difference between latitude and longitude. The latitude lines, the parallels, really do stay parallel to each other as they girdle the globe from the Equator to the poles in a series of shrinking concentric rings. The meridians of longitude go the other way: They loop from the North Pole to the South and back again in great circles of the same size, so they all converge at the ends of the Earth.
Here lies the real, hard-core difference between latitude and longitude—beyond the superficial difference in line direction that any child can see: The zero-degree parallel of latitude is fixed by the laws of nature, while the zero-degree meridian of longitude shifts like the sands of time.
The measurement of longitude meridians, in comparison, is tempered by time. To learn one’s longitude at sea, one needs to know what time it is aboard ship and also the time at the home port or another place of known longitude—at that very same moment. The two clock times enable the navigator to convert the hour difference into a geographical separation. Since the Earth takes twenty-four hours to complete one full revolution of three hundred sixty degrees, one hour marks one twenty-fourth of a spin, or fifteen degrees. And so each hour’s time difference between the ship and the starting point
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Those same fifteen degrees of longitude also correspond to a distance traveled. At the Equator, where the girth of the Earth is greatest, fifteen degrees stretch fully one thousand miles. North or south of that line, however, the mileage value of each degree decreases. One degree of longitude equals four minutes of time the world over, but in terms of distance, one degree shrinks from sixty-eight miles at the Equator to virtually nothing at the poles.
The active quest for a solution to the problem of longitude persisted over four centuries and across the whole continent of Europe.
English clockmaker John Harrison, a mechanical genius who pioneered the science of portable precision timekeeping, devoted his life to this quest. He accomplished what Newton had feared was impossible: He invented a clock that would carry the true time from the home port, like an eternal flame, to any remote corner of the world.
Long voyages waxed longer for lack of longitude, and the extra time at sea condemned sailors to the dread disease of scurvy. The oceangoing diet of the day, devoid of fresh fruits and vegetables, deprived them of vitamin C, and their bodies’ connective tissue deteriorated as a result. Their blood vessels leaked, making the men look bruised all over, even in the absence of any injury. When they were injured, their wounds failed to heal. Their legs swelled. They suffered the pain of spontaneous hemorrhaging into their muscles and joints. Their gums bled, too, as their teeth loosened. They gasped
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The moon travels a distance roughly equal to its own width every hour.
In spite of these obvious difficulties, Galileo had designed a special navigation helmet for finding longitude with the Jovian satellites. The headgear—the celatone—has been compared to a brass gas mask in appearance, with a telescope attached to one of the eyeholes. Through the empty eyehole, the observer’s naked eye could locate the steady light of Jupiter in the sky. The telescope afforded the other eye a look at the planet’s moons.
King Louis XIV of France, confronted with a revised map of his domain based on accurate longitude measurements, reportedly complained that he was losing more territory to his astronomers than to his enemies.
Jean Dominique as often as Giovanni Domenico.)
Roemer concluded, correctly, that the explanation lay in the velocity of light.
Roemer used the departures from predicted eclipse times to measure the speed of light for the first time in 1676. (He slightly underestimated the accepted modern value of 300,000 kilometers per second.)
(Multiplying a difference in hours by fifteen degrees gives only an approximation of location; one also needs to divide the number of minutes and seconds by four, to convert the time readings to degrees and minutes of arc.)
Aside from the fact that the great John Harrison built it, the clock claims uniqueness for another singular feature: It is constructed almost entirely of wood. This is a carpenter’s clock, with oak wheels and boxwood axles connected and impelled by small amounts of brass and steel. Harrison, ever practical and resourceful, took what materials came to hand, and handled them well. The wooden teeth of the wheels never snapped off with normal wear but defied destruction by their design, which let them draw strength from the grain pattern of the mighty oak.
sextant,
With detailed star charts and a trusty instrument, a good navigator could now stand on the deck of his ship and measure the lunar distances. (Actually, many of the more careful navigators sat, the better to steady themselves, and the real sticklers lay down flat on their backs.)
Halley set up a mini-Greenwich on the island of St. Helena. It was the right place but the wrong atmosphere, and Halley counted only 341 new stars through the haze.
What’s more, since the moon’s orbital motion varies cyclically over an eighteen-year period, eighteen years’ worth of data constitute the bare minimum groundwork for any meaningful predictions of the moon’s position.
As a result of this same failed attempt to measure stellar distances, Bradley arrived at a new, true value for the speed of light, improving on Ole Roemer’s earlier estimate.
Thus the lunar distance method was propagated by individual investigators scattered all across the globe, each one doing his small part on a project of immense proportions. No wonder the technique assumed an air of planet-wide importance.
In comparison, John Harrison offered the world a little ticking thing in a box. Preposterous!
Worse, this device of Harrison’s had all the complexity of the longitude problem already hardwired into its works. The user didn’t have to master math or astronomy or gain experience to make it go. Something unseemly attended the sea clock, in the eyes of scientists and celestial navigators. Something facile. Something flukish.
Rome wasn’t built in a day, they say. Even a small part of Rome, the Sistine Chapel, took eight years to construct, plus another eleven years to decorate, with Michelangelo sprawled atop his scaffolding from 1508 to 1512, frescoing scenes from the Old Testament on the ceiling. Fourteen years passed from the conception to the casting of the Statue of Liberty. The carving of the Mount Rushmore Monument likewise spanned a period of fourteen years. The Suez and Panama Canals each took about ten years to excavate, and it was arguably ten years from the decision to put a man on the moon to the
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Harrison had been aiming for compactness, mindful of the cramped quarters in a captain’s cabin. He never considered trying to make a longitude watch to fit in the captain’s pocket, because everyone knew that a watch could not possibly achieve the same accuracy as a clock.
Coming at the end of that big brass lineage, H-4 is as surprising as a rabbit pulled out of a hat.
Harrison loved it, and said so more clearly than he ever expressed another thought: “I think I may make bold to say, that there is neither any other Mechanical or Mathematical thing in the World that is more beautiful or curious in texture than this my watch or Timekeeper for the Longitude … and I heartily thank Almighty God that I have lived so long, as in some measure to complete it.”
prig,”
As astronomer royal, Bradley served on the Board of Longitude, and was therefore a judge in the contest for the longitude prize. This description of William’s makes it sound as though Bradley himself was also a contender for the prize. Bradley’s personal investment in the lunar distance method could be called a “conflict of interest,” except that the term seems too weak to define what the Harrisons stood up against.
Maskelyne produced the first volume of the Nautical Almanac and Astronomical Ephemeris in 1766, and went on supervising it until his dying day. Even after his death, in 1811, seamen continued relying on his work for an additional few years, since the 1811 edition contained predictions straight through to 1815. Then others took over the legacy, continuing the publication of the lunar tables until 1907, and of the Almanac itself up to the present time.
mien.
Sauerkraut. That was the watchword on Captain James Cook’s triumphant second voyage, which set sail in 1772. By adding generous portions of the German staple to the diet of his English crew (some of whom foolishly turned up their noses at it), the great circumnavigator kicked scurvy overboard.
Cook made it his oceangoing vegetable, and sauerkraut went on saving sailors’ lives until lemon juice and, later, limes replaced it in the provisions of the Royal Navy.
The king then interviewed William at length at Windsor Castle. In a later account of this pivotal meeting, written in 1835 by William’s son, John, the king is reported to have muttered under his breath, “These people have been cruelly treated.” Aloud he promised William, “By God, Harrison, I will see you righted!
After ten weeks of daily observations between May and July 1772, he felt proud to defend this new timekeeper, for H-5 had proved accurate to within one-third of one second per day. He took
aegis
abstruse.
