Although latitude has an obvious zero line at the equator, longitude had no recognizable zero line. Mapmakers were free to choose an arbitrary line, usually a known longitude within their country. Ptolemy chose to have the zero longitude line pass through the Canary Islands. Later chosen were Paris, Rome, St Petersburg, and Philadelphia, among others. Finally in 1767 the world began to use London, specifically the observatory in Greenwich outside London. Drawing latitude and longitude on a map does not solve the problem of navigating safely to a destination. There must be a way to determine longitude while on a rolling ship.
The basics of finding longitude were well known. It was recognized that longitude could be determined by simply finding the time on a ship and the time at some known meridian at home. If this time difference could be determined at a given moment then the simple rule of fifteen degrees of longitude for each hour of time difference could be applied. This concept is simple but in practice it was out of reach for lack of a reliable method of time measurement on board a ship.
One bizarre suggestion for telling time at home port was the wounded dog technique. This method depended on a miraculous substance called “powder of sympathy.” This mysterious powder was able to heal wounds from any distance merely by applying it to a piece of bandage that had been on an injured person. The important element of the procedure was that the patient felt a sharp pain at the moment the powder came in contact with a bandage that had touched the wound.
Applying this strange phenomenon to finding latitude would require having a wounded dog on board every ship. Supposedly when the clock in London struck noon, someone there would dip bandages from all the dogs in the sympathy powder and the wounded dogs on ships anywhere in the world would yelp in pain, signaling that it was then noon in London. If a ship’s navigator could then determine the solar time aboard ship he could calculate longitude. Even if the preposterous notion of sympathy powder were valid, the method would require a wounded dog on each ship and a person to dip many pieces of bandage in the powder at noon each day. Furthermore the poor dog’s wound would have to be kept open so the system could continue working. Fortunately this idea was never really taken seriously by anyone as no one could produce the powder of sympathy.
Three more realistic methods evolved for finding longitude while navigating a ship and the earliest of these did not involve knowing time. It was called dead reckoning. This approach began from a port of known longitude and a careful record of direction, speed, and time traveled was kept using a sand glass. Even the most skilled and careful navigator made errors that could accumulate into large errors on a long voyage. Ships at sea were never certain of their location using dead reckoning. A comparison of old maps with recent maps often shows fairly good agreement with latitude but great distortions due to errors in longitude. An even worse outcome from longitudinal errors is running aground. Errors in longitude resulted in many shipwrecks.
A second method involves finding time at the Prime Meridian (zero longitude) by a technique called lunar distance. This required measuring the angle between the moon and a star. At that moment anyone on the surface of the earth who can see the same two bodies will observe the same angle between them after certain routine corrections. The navigator then consults a prepared table of lunar distances and the times at which they will occur. By comparing the corrected lunar distance with the tabulated values, the navigator finds the Greenwich time for that observation. A major problem was that these measurements require greater accuracy than can be obtained on a rolling ship. The observer must be on a stable surface to measure angles.
The British Board of Longitude announced a prize of £20,000 for the person who devised a method that could stand the test of a voyage to the West Indies and back with a maximum error of thirty minutes (0.5°) longitude. This was a princely sum comparable to $4,000,000 today. The membership of the Board consisted of scientists, naval officers, and government officials, plus a group of ex-officio members who acted as advisors to the Board of Longitude. The advisors included the Astronomer Royal, John Flamsteed, the president of the Royal Society, Sir Isaac Newton, and prominent mathematicians from Oxford and Cambridge among others. From the composition of the Board it might be expected that they anticipated an astronomical solution to longitude.
When the Board announced its enticing prize many proposals were submitted including numerous crackpot ideas. Most proposals submitted for the Board’s consideration were variation’s on the lunar distance approach. Although the lunar distance method was complicated and impractical, the use of a clock for finding longitude was deemed impossible for the accuracy required.
This brings us to the third method for finding longitude: the clock. The best clocks of the day were regulated by a pendulum requiring a stable platform and even the most accurate would lose several minutes per day. In 1675 a Dutch astronomer and mathematician, Christiaan Huygens, invented a chronometer regulated by a balance wheel and a spiral spring rather than a pendulum. This innovation became the basis for pocket watches. Huygens tested his invention at sea, but it never achieved the accuracy needed for navigation. Several others attempted to refine the concept but they came to nothing.
Jeremy Thacker developed some important ideas to improve accuracy, such as enclosing the works in a glass vacuum chamber to eliminate changes in atmospheric pressure, a winding mechanism that prevented the clock stopping while being wound, and mounting the instrument on gimbals to reduce the effect of the rolling at sea. Thacker introduced the name “chronometer” to highlight the greater accuracy of his clock. Still it was not accurate enough for navigation. The problem was that temperature changes caused expansion and contraction of every important metal in the clock, causing it to gain and lose depending on air temperature.
Enter John Harrison, a carpenter and cabinet maker from Yorkshire born in 1693, who as a boy taught himself to read and write. Later he avidly read books such as “Saunderson’s Mechanicks” and Newton’s Principia. Although Harrison had never worked with a clockmaker, he built his first pendulum clock in 1713 made almost entirely of wood, including all wheels and axles. Harrison could see that the pendulum clock would never win the big prize for a navigation clock, so he designed one with a set of counter-oscillating rods that were counterbalanced to maintain precise motion in the stormiest sea.
In 1730 Harrison took his plans directly to the then Astronomer Royal, Edmund Halley, who saw some promise but discouraged Harrison with the news that the Board’s bias was toward an astronomical solution to longitude rather than a mechanical. Halley, however, kindly recommended that Harrison talk to the most respected instrument maker in England and a Fellow of the Royal Society, George Graham. Harrison was wary at first that Graham would steal his idea, but in a few hours of discussion Graham became a helpful mentor in the project.
Five years later in 1735, Harrison completed H-1: Harrison’s No. 1. This fascinating clock is twenty-five inches high, still operating, and on display in the Royal Observatory of the National Maritime Museum in Greenwich. Its shiny brass parts with oscillating rods look more like a Rube Goldberg device than a clock, but it is an elegant sight to behold. Harrison took his clock to Graham who showed it to the Royal Society where it was acclaimed. The first test came a year later on a trip to Portugal, not the West Indies as prescribed. Harrison went on the voyage with the clock and it proved a resounding success. He took it before a meeting of the Board with several members already in full support. Surprisingly, at that meeting Harrison decided to ask for more time and funds to build a smaller version with even greater accuracy. The Board could hardly refuse such an offer and granted £250 plus another £250 when he finished the second version. Harrison left the meeting full of confidence that the £20,000 would be his.
In 1741 Harrison brought H-2 to the committee. It was only slightly smaller and incorporated a number of improvements. This clock was given several rigorous and successful tests by the Royal Society, who declared it ready for a sea test. At this point Harrison again balked, telling the Board he still saw ways for improvement. He spent almost seventeen years persistently working on H-3 while collecting an occasional £500 grant from the Board. This third clock, H3, was designed with circular balances, roller bearings, and most importantly bi-metallic (brass and steel) parts that could automatically compensate for temperature changes. Each of these innovations is still in use today. Its distinctive feature was an oscillating balance wheel powered by a bi-metallic spring for temperature compensation.
In the meantime the venerable Astronomer Royal, Edmund Halley, died and was replaced by James Bradley. Also improved tables and methods for the lunar distance method had come to the attention of the Board of Longitude. Bradley, being an astronomer, had a strong inclination to favor the lunar distance method, and felt Harrison’s clock was unseemly simple. The feeling of the Board began to shift in favor the lunar distance method over Harrison’s clock.
By 1757 John Harrison had made H-3, which was still about twenty-four inches high. Although he felt it was a suitable size, Harrison was still not satisfied with its performance, and moved on to work on H-4.
Harrison began to see that other clockmakers were using some of his innovations to improve the accuracy of pocket watches. This moved him to consider a new version of his clock. In 1759 he completed his H-4 which now looked like an oversized pocket watch (5” diameter and 3 pounds in weight). Harrison was finally happy with his clock and declared, …”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 God that I have lived so long, as in some measure to complete it.” Harrison was then 66 years old and had worked on navigation clocks for about twenty-nine years—with subsistence grants, but no prize—to produce the most important timepiece ever built. In the Greenwich Maritime Museum the original H-4 is still operational but is never allowed to run so it can be preserved in its pristine state.
The rest of Harrison’s story concerns his long ordeal convincing the Board that his clock was better than the lunar distance method they now favored. A voyage to test H-4 was planned in May 1761, then delayed and delayed again until November in what may have been a ploy by Astronomer Royal Bradley in favor of the lunar method. When the ship arrived in Jamaica in mid-January, a time check showed a loss of only five seconds in 81 days at sea. Upon return to England at the end of March the total error for the voyage was under two minutes. Harrison had met all the requisites of the Board and the prize should have been his immediately. The Board, however, felt uncertain that certain prescribed procedures may not have been followed and that a second more rigorous test must be made. New conditions were added to the test in a prime example of moving the goal post just as you’re about to score.
Naturally Harrison’s frustration grew as his hopes declined and he vowed not to comply with the new abominable demands, some of which were imposed on his clocks but not on the lunar method. Eventually he gave into their demands. The Board required that Harrison give them his existing clocks, H-1 through H-4 and all drawings and descriptions, in an effort to be certain that there was no element of luck in construction of the clock. Then Harrison was required to build two replicas. As assurance of their good intentions the Board then gave him £10,000 of the prize money.
In 1775 Captain James Cook returned from his second voyage into the Pacific Ocean during which he carried a replica of Harrison’s H-4. It was made by Larcum Kendall and labelled K-1. Captain Cook gave high praise to the effectiveness of the timepiece for navigation. Not surprisingly, this endorsement by such a renowned mariner carried great weight with the Board. Incidentally, this K-1 clock cost £450, which today would be about $72,000--too expensive for many mariners when a good sextant cost only £20.
John Harrison’s H-4 ultimately passed all the required tests. He produced a replica, H-5, and received the remainder of the prize money in 1773—forty-three years after first presenting his revolutionary idea, but not without additional haranguing with the Board. He died three years later at the age of eighty-three.
Nye, Eric W. Pounds Sterling to Dollars: Historical Conversion of Currency, retrieved from website: www.uwyo.edu/numimage/currency.htm. (no date shown)
Sobel, Dava. Longitude, The true story of a lone genius who solved the greatest scientific problem of his time. New York: Walker and Company. 1995. (A most engaging little book even if you never wondered about finding longitude.)
Wikipedia. John Harrison. Retrieved from website: en.wikipedia.org/wiki/John_Harrison
Wikipedia. Marine Chronometer. Retrieved from website: en.wikipedia.org/wiki/Marine_chronometer