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by
Dava Sobel
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. This
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
Every day at sea, when the navigator resets his ship’s clock to local noon when the sun reaches its highest point in the sky, and then consults the home-port clock, every hour’s discrepancy between them translates into another fifteen degrees of longitude.
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.
For lack of a practical method of determining longitude, every great captain in the Age of Exploration became lost at sea despite the best available charts and compasses. From Vasco da Gama to Vasco Núñez de Balboa, from Ferdinand Magellan to Sir Francis Drake—they all got where they were going willy-nilly, by forces attributed to good luck or the grace of God.
In the course of their struggle to find longitude, scientists struck upon other discoveries that changed their view of the universe. These include the first accurate
determinations of the weight of the Earth, the distance to the stars, and the speed of light. As
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. Harrison,
a man of simple birth and high intelligence,
“dead reckoning”
dead reckoning marked him for a dead man.
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
for breath, struggled against debilitating weakness, and when the blood vessels around their brain...
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The souls of Sir Clowdisley’s lost sailors— another two thousand martyrs to the cause—precipitated the famed Longitude Act of 1714, in which Parliament promised a prize of £20,000 for a solution to the longitude problem. In
The moon travels a distance roughly equal to its own width every hour. At
From the dance of his planetary moons, Galileo worked out a longitude solution. Eclipses
Galileo’s method for finding longitude at last became generally accepted after 1650—but only on land. Surveyors and cartographers used Galileo’s technique to redraw the world.
Indeed, 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.
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.)
Time is to clock as mind is to brain.
like a heartbeat or an ebb tide, timepieces don’t really keep time. They just keep up with it, if they’re able.
(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.)
he applied the word cell to describe the tiny chambers he discerned in living forms.
Hooke had his hand in fathoming the behavior of light, the theory of gravity, the feasibility of steam engines, the cause of earthquakes, and the action of springs.
The Hooke-Huygens conflict over the right to an English patent for the spiral balance spring disrupted several meetings of the Royal Society, and eventually the matter was dropped from the minutes, without being decided to either contestant’s satisfaction. In
The separate failures of these two giants seemed to dampen the prospects for ever solving the longitude problem with a clock. Disdainful
Admiral Shovell’s disastrous multishipwreck on the Scilly Isles after the turn of the eighteenth century intensified the pressure to solve the longitude problem.
Two infamous entrants into the fray in the aftermath of this accident were William Whiston and Humphrey Ditton, mathematicians and friends, who often engaged each other in wide-ranging discussions.
counting the seconds elapsed between a flash of lightning and a clap of thunder.
First a new breed of fleet must be dispatched and anchored at 600-mile intervals in the oceans.
They stated the depth of the North Atlantic as 300 fathoms at its deepest point, when in fact the average depth is more like 2,000 fathoms, and the sea bottom occasionally dips down to more than 3,450.
The Harrison brothers tested the accuracy of their gridiron-grasshopper clocks against the regular motions of the stars. The
In these late-night tests, the Harrisons’ clocks never erred more than a single second in a whole month. In comparison, the very finest quality watches being produced anywhere in the world at that time drifted off by about one minute every day.
country bumpkins
Harrison saw he’d have to jettison his gridiron pendulum in order to win the £20,000.
In place of the striated, swinging stick with its hanging bob, Harrison began picturing a springing set of seesaws, self-contained and counterbalanced to withstand the wildest waves.
took him almost four years,
John Harrison arrived in London in the summer of 1730,
one of the most famous members of the Board of Longitude—the great Dr. Edmond
Halley—and he headed straight for the Royal Observatory at Greenwich to find him.
Halley had become England’s second astronomer royal in 1720, after John ...
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And of course Flamsteed never forgave Halley, or his accomplice Newton, for pilfering the star catalogs and publishing them against his will.
Halley knew that the Board of Longitude would not welcome a mechanical answer to what it saw as an astronomical question.
Halley sent him to see
the well-known watchmaker George Graham.
“Honest” George...
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the best judge of the sea clock Harrison pro...
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Graham, who was about twenty years older than Harrison, became his patron at the end of one long day together.
Harrison spent the next five years piecing together the first sea clock, which
H-1 now lives and works (with daily winding) in an armored-glass box at the National Maritime Museum in Greenwich, where it still runs gamely in all its friction-free glory,
