The Quest to Solve the “Longitude Problem”
On October 22, 1707, a squadron of British naval ships sailed toward the English Channel. But they miscalculated their position. The result? Four ships were wrecked on the Isles of Scilly, an island group in the Atlantic Ocean southwest of Land’s End, England. Nearly 2,000 men perished.
SAILORS in those days could easily measure their latitude—their distance north or south of the equator. But they had no accurate way of measuring their longitude—how far east or west they had traveled. By the early 18th century, hundreds of ships were plying the Atlantic each year, and shipwrecks were common. But it was the disaster of 1707 that focused English minds on the longitude problem, as it was called.
In 1714 the British Parliament offered a prize of 20,000 pounds to anyone who could accurately determine longitude at sea. Today that prize would be equivalent to several million U.S. dollars.
Ascertaining longitude was extremely difficult because it required precise timekeeping. To illustrate: Imagine that you live in London. At noon you receive a phone call from a person who lives at the same latitude as you, but her clock reads 6:00 a.m. on the same day. This puts her six hours behind you. You know your geography, so you rightly deduce that she lives in North America, where the sun is just coming up. Now imagine that you know her precise local time to the very second, not according to a broad time zone, but according to her actual position in relation to the sun. You could calculate her longitude very accurately.
Centuries ago, a navigator anywhere on earth could determine noon locally by simply looking at the sun. If he also knew the time back home accurately enough, he could plot his longitude to within some 30 miles [50 km]. That, in fact, was the accuracy required at the end of a six-week-long voyage to win the aforementioned prize.
The challenge, however, was to know the precise time back home. The navigator could carry along a pendulum clock, but that would not work on a ship tossed by high seas, and clocks with springs and wheels were still crude and inaccurate. Clocks were also influenced by changing temperatures. But what about the big clock around us—the celestial bodies, including the moon?
An “Astronomical” Task
Astronomers proposed a theory of measurement called the lunar distance method. The concept involved preparing tables that would help navigators determine their longitude according to the location of the moon in relation to certain stars.
For more than a century, astronomers, mathematicians, and navigators wrestled with the problem, but the complexities hampered progress. In view of the formidable obstacles, the expression “discovering the longitude” came to refer to any problem that seemed insurmountable.
A Carpenter Accepts the Challenge
A village carpenter named John Harrison, from the Lincolnshire village of Barrow Upon Humber, decided to tackle the longitude problem. In 1713, before he was 20 years old, Harrison built a pendulum clock almost entirely of wood. Later, he invented mechanisms to reduce friction and compensate for temperature changes. At that time the world’s finest watches erred by a minute a day, but Harrison’s clocks were accurate to one second a month.*
Harrison then turned his attention to the challenges of keeping accurate time at sea. After pondering the matter for four years, he set off for London to submit his proposal to the Board of Longitude, which was empowered to award the prize. There Harrison was introduced to leading watchmaker George Graham, who gave him a generous, interest-free loan to build a timepiece. In 1735, Harrison presented the world’s first accurate marine chronometer before a delighted Royal Society, a body of the most distinguished scientists in Britain. The clock weighed 75 pounds [34 kg] and gleamed with brass.
Harrison and his clock were sent on a sea trial to Lisbon—not the West Indies, as required to win the prize—and the device performed admirably. He could have demanded an immediate cross-Atlantic trial to demonstrate that his clock was worthy of the prize. In fact, at the first meeting of the Board of Longitude, the only one who criticized the clock was Harrison himself! A perfectionist, he felt that he could improve the design. So he merely asked for a little money and more time to build an even better timepiece.
Six years later Harrison’s second chronometer, which weighed 86 pounds [39 kg] and included several improvements, won the full support of the Royal Society. But Harrison, now 48 years old, was still not satisfied. He returned to his workshop and spent the next 19 years toiling on a third, quite different, design.
While working on his hefty third model, Harrison discovered something quite by accident. A fellow clockmaker built a pocket watch based on a design by Harrison. It had always been assumed that large clocks would be more accurate than pocket watches. But Harrison was amazed at the accuracy of the new device. So when a cross-Atlantic test was finally arranged in 1761, he placed his full confidence, not in his third design, but in his fourth, a three-pound [1 kg] chronometer based on the pocket-watch design. Harrison allegedly stated: “I heartily thank Almighty God that I have lived so long, as in some measure to complete it.”
By this time, however, astronomers were close to succeeding with their method to determine longitude. In addition, the person who now dominated the panel of judges authorized to issue the prize money was an astronomer, Nevil Maskelyne. Harrison’s timepiece was put to the test by means of an 81-day Atlantic crossing. How did the device perform? It lost a mere five seconds! Nevertheless, the judges delayed awarding Harrison the prize, claiming that certain rules had been broken and that the accuracy of the timepiece was just good luck. As a result, he received only part of the prize. Meanwhile, in 1766, Maskelyne published tables of the moon’s predicted positions that enabled navigators to calculate their longitude in only half an hour. Harrison feared that Maskelyne himself might take the prize.
Then, in 1772, British explorer Captain James Cook entered the scene. On his second historic voyage, Cook used a duplicate of Harrison’s timepiece, later reporting that it exceeded all expectations. Meanwhile, Harrison, now 79, became so frustrated with the Board of Longitude that he appealed to the king of England. As a result, Harrison received the balance of the prize money in 1773, although he was never officially declared the winner. John Harrison died three years later, on his 83rd birthday.
Within a few years, accurate marine chronometers could be purchased for 65 pounds. Yes, the impossible had become reality, thanks largely to the brilliance and dedication of a village carpenter.
Harrison, aided by his brother, measured the accuracy of his timepiece over many nights by marking the precise moment when certain stars disappeared from his view behind a neighbor’s chimney.
[Diagram/Picture on page 21]
(For fully formatted text, see publication)
Determining your longitude using time
6:00 A.M. 12 NOON
NORTH AMERICA BRITAIN
[Picture on page 22]
Clockmaker John Harrison
[Picture on page 22]
Harrison’s first design, a 75-pound chronometer
National Maritime Museum, Greenwich, London, Ministry of Defence Art Collection
[Picture on page 22]
Harrison’s fourth design, a three-pound chronometer (not to scale)
[Picture Credit Lines on page 20]
Ship in distress: © Tate, London/Art Resource, NY; compass: © 1996 Visual Language