The Board of
many of whom
did not even
Persistence and Genius
|Book Review by Jeanine DeNoma|
Skeptics are familiar with the lone kook who, opposed by science, spends a lifetime pursuing solutions that defy the laws of the universe. Longitude presents a refreshing twist: a lone genius who through his persistence and lifetime dedication really does solve the greatest scientific problem of his time.
Beginning with the nautical explorations of the 1400s through the expansion of the global shipping industry well into the late 1700s, determining longitude was the great scientific problem. It's solution evaded almost every great name in science, but was eventually solved by a self-taught watchmaker named John Harrison. Sobel weaves the tale of the longitude solution into a fascinating narrative of personalities and events encompassing three centuries.
Ships, lives and fortunes were lost for lack of an effective method for determining longitude. Treacherous rocky coast lines appeared suddenly where by all reckoning they should not be. After months at sea, land with its fresh water and food supplies, did not appear when it was expected. By the seventeenth century, 300 ships a year sailed between Britain and the West Indies. Without a means to determine longitude, ships stayed within narrowly defined shipping lanes, making them easy prey for pirates.
"Captains of the fifteenth, sixteenth, and seventeenth centuries relied on 'dead reckoning' to gauge their distance east or west of home port. The captain would throw a log overboard and observe how quickly the ship receded from this temporary guidepost. He noted the crude speedometer reading in his ship's log, along with the direction of travel, which he took from the stars or a compass, and the length of time on a particular course, counted with a sandglass or a pocket watch. Factoring the effects of the ocean currents, fickle winds, and errors in judgement, he then determined longitude," writes Sobel.
The lines of latitude run parallel to one another around the globe in concentric circles from the poles to the equator. One can easily determine his latitude from daylength, the height of the sun, or the position of known stars in relation to the horizon. The question of one's longitudinal position is an entirely different problem. Lines of longitude are arbitrary. Zero degree longitude has at various times been set to run through the Canary Islands, the Azores, Cape Verde Islands, Rome, Copenhagen, Jerusalem, St. Petersburg, Pisa, Paris and Philadelphia before finally settling in London. Two competing methods, astronomical observations and clocks, were proposed as a means of finding a ship's location among these imaginary lines.
In 1514 the German astronomer Johannes Werner proposed the "lunar distance method," mapping the positions of fixed stars and calculating longitude from the passage of the moon across each one. Eventually, to this end, the Royal Observatory in Greenwich was built under the direction of Robert Hooke and the architect of St. Paul's Cathedral, Christopher Wren. John Flamsteed was installed as the first astronomer royal in 1675. Flamsteed spent 40 years compiling a catalog of the fixed stars.
Galileo, after his discovery of the moons of Jupiter in 1610, proposed that longitude be calculated from their eclipses, which occurred over 1000 times a year with "clockwork regularity." In fact by 1650 land surveyors and cartographers routinely used this method. It was not suitable, however, for navigation where Jupiter's moons were nearly impossible to see from a rocking ship and where longitude needed to be determined in bad weather and during the day, as well as at night.
Flemish astronomer Gemma Frisius (1530), Englishman William Cunningham (1559), and navigator Thomas Blundeville (1622) each suggested finding longitude using mechanical timepieces. By knowing the exact time at one's current location and the exact time at that same moment at a known longitudinal reference point, one could convert the difference to degrees on the globe. With an accurate timepiece, the navigator could reset the ship's clock to local time at noon each day and then use the home port's clock to calculate his degrees longitude. When combined with latitudinal information, longitude could be converted to distance. "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," explains Sobel. No clocks of the time, however, were sufficiently accurate to be useful on this account. And accurate timekeeping at sea presented special problems posed by the ship's motion, salty air, humidity, temperature fluctuations and the large size of clocks.
After an especially disastrous loss to the Royal Navy and under prodding by sea merchants and ship captains, the British Parliament passed the Longitude Act of 1714. Sir Isaac Newton and Edmond Halley were brought in as Parliamentary advisors. In his speech to Parliament, Newton discussed the problems inherent in calculating longitude using the lunar distance method, the moons of Jupiter, and clocks. The Longitude Act established rewards for "Practical and Useful" means of determining longitude at sea. The amount of 20,000 pounds would be awarded for a method accurate to within half a degree, 15,000 pounds for accuracy within two-thirds of a degree, and 10,000 pounds for accuracy within one degree. An official Board of Longitude, made up of scientists, naval officers and public officials, was to pass judgement on the worthiness of a method and award development money to individuals with promising ideas.
As skeptics are well aware, when there is fame or money to be gained, cranks come out of the woodwork. Sobel devotes an entire chapter to crank methods for finding longitude. These include "sympathy powder," magnetic variation, a design to draw longitudinal meridians in the night sky, and a proposal to place cannons at intervals across the oceans and use calculations based on the speed of sound. The Board of Longitude did not meet for the first fifteen years after its formation. It simply sent rejection letters to petitioner after petitioner, many of whom did not even consider the nature of the problem and sent "blueprints for perpetual motion machines and proposals that purported to square the circle or make sense of the value of pi."
The Board convened for the first time in 1737 to evaluate a timepiece presented by clockmaker John Harrison. Harrison had the support of then astronomer royal Dr. Edmond Halley and a well-known London clockmaker, George Graham. Over the next 25 years Harrison was to present the Board with four more timepieces. This first clock, called H-1, received favorable reports from its test voyages and should have qualified Harrison for the prize. But Harrison, a perfectionist, simply asked the Board for money to work on a better model.
H-1 weighed 75 pound and was four feet square. It still runs friction-free in the National Maritime Museum in Greenwich. Harrison's next clock, H-2, was smaller but heavier and featured "a mechanism to ensure a uniform drive and a more responsive temperature compensation devise, each of which constituted a minor revolution in precision," writes Sobel. H-3, which weighted 60 pounds and had 753 moving parts, took Harrison 19 years to build. In doing so, he invented the bi-metallic strip, still used in thermostats today, and caged ball bearings, now found in almost every machine with moving parts. But Harrison's masterpiece was H-4. Completed in 1759, it was unlike any of his previous clocks. H-4 weighted only three pounds, measured five inches in diameter, and had anti-friction devices made of diamonds and rubies.
The scientific community was biased in favor of an astronomical solution. The Reverend Nevil Maskelyne, appointed the fifth astronomer royal in 1765 (and therefore on the Board of Longitude) was not only committed to the lunar distance method, but had aspirations for developing that method. Harrison, who probably qualified for the prize in 1735, required the intervention of King George III to receive his monetary reward in 1773. He was not, however, awarded the prize. It went unclaimed until the Longitude Act was repealed in 1828.
Sobel skillfully tells this exceptional story. Her characterizations of the conflicted interactions between Harrison and the Board of Longitude with his chief nemesis, Maskelyne, are vivid. And her depictions of the elegance of the Harrison's timepieces left me feeling as if I had seen them.
As the Philadelphia Inquirer's cover promotional says, this story
is "as much a tale of intrigue as it is of science... a book full of gems
for anyone interested in history, geography, astronomy, navigation, clockmaking,
and - not the least - plain old human ambition and greed."
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