The Longitude Prize: John Harrison's Journey to Revolutionize Navigation
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Chapter 1: The Quest for Longitude
Navigating the seas has always posed significant challenges for mariners, particularly when it comes to determining their location without land in sight. While calculating latitude—how far north or south one is—can be done by observing the Sun's position, pinpointing longitude—one's position east or west—remains far more difficult.
To ascertain longitude, sailors have traditionally relied on two methods. The first involves using the night sky, particularly the Moon's position, in a technique known as "lunar distance." However, this method is limited to nighttime and lacks precision. The alternative requires a reliable clock set to the time of a known location, such as the home port, which can be compared with the local time.
Determining local time is feasible based on the Sun's position, but the challenge lies in knowing the time at a distant port, potentially weeks or months away. In the early 18th century, no clock existed that was sufficiently accurate for maritime conditions, especially on a vessel battling the elements.
The Royal Observatory in London was established in 1675 with the aim of solving this pressing longitude dilemma. By 1714, however, it had only succeeded in improving upon the lunar distance method. Consequently, the British Government enacted the Longitude Act, offering a substantial reward of £20,000 (equivalent to millions today) to anyone who could develop a dependable marine timepiece. This reward underscores the gravity of the issue, as Great Britain aspired to dominate the seas while suffering significant losses due to navigational errors.
Enter John Harrison
The key figure who addressed this challenge was John Harrison (1693–1776), a self-taught carpenter from Lincolnshire with a passion for clock-making. Despite having built only a few wooden clocks prior to pursuing the longitude prize, he had made notable advancements in clock accuracy and believed he possessed the solution.
In 1726, he learned of the unclaimed prize and, by 1730, designed a portable version of his best long-case clock. After presenting his designs to Edmond Halley, the Astronomer Royal, he was encouraged to seek the advice of renowned clockmaker George Graham. Graham, impressed with Harrison's design, financed the creation of a prototype clock.
This first clock, known as “H1,” was completed by 1735. Although portable for its time, it weighed 72 pounds. Following recommendations from Halley and Graham, H1 was tested at sea during a voyage to Lisbon in 1736. The clock's accuracy improved the ship's navigation by one and a half degrees, resulting in a £500 award from the Board of Navigation to further develop an enhanced prototype.
Harrison's subsequent prototypes, H2 and H3, faced various challenges, but the breakthrough came with H4, which was constructed with a new design approach.
H4 was a large pocket watch, over five inches in diameter and weighing just three pounds. Harrison initially intended this device to transfer time from land to sea, enabling the ship's timepiece to be accurately set before departure. To his surprise, H4 performed beyond expectations, rendering the bulky sea clock unnecessary.
How John Harrison Eventually Won His Reward
The prize's conditions stipulated that the timepiece must be tested on a voyage to the West Indies, a common route during the slave trade. Full payment of £20,000 was contingent upon achieving a longitude accuracy within 30 miles; failure to meet this would reduce the award to £10,000.
In 1761, during a trial, H4 lost only 5.1 seconds over an 81-day round trip, though this figure included adjustments based on the clock's known performance. Unfortunately, this lack of clarity led to disqualification, and Harrison received only £2,500, contingent upon a second trial.
The subsequent trial in 1764 showed a gain of one second daily. Over a 47-day outer voyage, H4 allowed for longitude calculations within 10 miles—three times the required accuracy. Despite this, the Board of Longitude was skeptical of the watch's precision and imposed numerous conditions before awarding the prize. Harrison was directed to create two additional watches and submit the original for examination by a committee. Only if an independent craftsman could replicate it would he receive the remaining £10,000.
When the committee convened in August 1765 and evaluated H4 in Harrison's presence, they were impressed enough to award him half the original prize. However, Harrison was determined to secure the full amount.
After Larcum Kendall, a master watchmaker, successfully replicated H4 in 1769, this watch accompanied Captain Cook on his voyages of discovery, aiding in mapping the South Pacific.
Before Harrison could produce another timepiece, mariners gained access to the sextant, allowing for more precise local time calculations, which rendered the lunar distance method increasingly viable. Harrison was compelled to create something even more accurate than H4, yet he was denied access to his own invention while constructing the new watch, designated H5.
In his pursuit of H5's testing and the remaining £20,000, Harrison had to appeal to the King. In 1772, H5 was evaluated by the Royal Observatory, demonstrating timekeeping accuracy within a third of a second daily. Nevertheless, the Board refused to recognize the results. It wasn't until Harrison appealed to Prime Minister Lord North that a new Act of Parliament passed in 1773, finally awarding him the full prize.
By then, Harrison was elderly and had only three years left to enjoy the recognition he so richly deserved, passing away in 1776, believed to be on his 83rd birthday.
The Board of Navigation likely never expected anyone to fulfill the prize's extensive requirements, which had remained unclaimed since 1714. Their reluctance to award it to a joiner turned clockmaker, perceived as an amateur, highlights their skepticism. However, John Harrison was exceptionally resourceful and dedicated years to perfecting his craft.
One of Harrison's key innovations was the bimetallic strip, a combination of two metals that compensates for temperature changes due to their differing expansion rates. This principle is still utilized in many modern inventions, including electric toasters. In timepieces, this mechanism prevents warping from temperature fluctuations, ensuring accuracy.
The contemporary marine chronometer, developed from Harrison's designs, empowered the British Navy to explore and map the world's oceans for the following 200 years, solidifying Great Britain's status as a global power through its naval dominance.
Although satellite technology has transformed navigation, making much of Harrison's work obsolete, his contributions should not be overlooked. His dedication undoubtedly saved countless lives.
For further reading, see my lists on:
British History
Science
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Chapter 2: Impact of the Chronometer
The significance of Harrison's inventions cannot be overstated. His remarkable journey led to the creation of the marine chronometer, a device that transformed maritime navigation.
This video, "The Clock That Changed the World (BBC History of the World)," delves into the profound impact of Harrison's chronometer on global exploration and navigation.
Chapter 3: The Legacy of the Longitude Solution
In addition to revolutionizing navigation, Harrison's work laid the groundwork for future advancements in timekeeping and exploration.
Explore the fascinating narrative in the video, "How Did The Chronometer Change The World? (John Harrison Marine Chronometer & The Longitude Problem)," which examines the legacy of Harrison's contributions to maritime history.