The Longitude Prize and the Harrison Chronometer

Updated on April 24, 2017
Portrait of John Harrison by Thomas King
Portrait of John Harrison by Thomas King

The Longitude Problem

One of the greatest problems that marine navigators face is working out where they are when out of sight of land. Knowing one’s latitude (i.e. how far north or south) is not too difficult, because the height of the Sun in the sky will tell one this, but navigation also relies on pinpointing one’s longitude, or position east or west, which is harder to determine.

In order to determine longitude, there are two possible methods. One is to use the night sky, including the position of the Moon, as a kind of celestial clock. This is the “lunar distance” method, but it has the obvious disadvantage that measurements can only be made at night, and is not particularly accurate. The other is to have on board a clock that is set to the time at some predetermined place, such as one’s home port, that can be compared to local time.

It is not difficult to work out the current local time, based on the Sun’s position, but the problem is knowing what the time is at the port that could have been left weeks or months before. In the early 18th century there was no clock available that could be relied upon to be accurate enough, especially on a ship at sea that was subject to being tossed about by wind and waves.

The Royal Observatory in London had been established in 1675 with the sole purpose of solving the problem of finding longitude at sea, but by 1714 it had produced nothing better than the lunar distance method. The British Government therefore passed the Longitude Act which offered a prize of 20,000 pounds (several million in modern money) to anyone who could devise a timepiece that could operate with accuracy at sea. The size of the reward shows just how serious this issue was. Great Britain was now a maritime nation that wished to “rule the waves”, but the huge losses of ships at sea, caused by navigational errors, presented a severe handicap to this ambition.

Enter John Harrison

The man who solved the problem was John Harrison (1693-1776), a carpenter’s son from Lincolnshire with no formal education but with an interest in clocks. Although he had only built a few wooden clocks before seeking the longitude prize, he had made several important advances in their accuracy and believed that he had the answer.

He heard about the yet-to-be-claimed prize in 1726, and in 1730 had designed a portable version of his best long-case clock. He showed his drawings to Edmond Halley, the Astronomer Royal, who advised him to consult a well-known clockmaker named George Graham. Graham was impressed by the design and lent Harrison the money to build a prototype clock.

This clock, now referred to as “H1” was completed by 1735. Although portable by the standards of the day, it still weighed 72 pounds. Halley and Graham recommended that it should be tested at sea, and this was done in 1736 on a voyage to Lisbon. Harrison’s clock was accurate enough to correct the ship’s reckoning by one and a half degrees, which was sufficient to persuade the Board of Navigation to give Harrison an award of 500 pounds to allow him to make an improved prototype.

The next two prototypes, H2 and H3, were even heavier than H1, and beset with various technical problems, but the real breakthrough came with H4, which was built to a different specification altogether.

This was a large pocket-watch, more than five inches in diameter but only weighing three pounds. Harrison had intended to use this only as a means of “transferring” time from land to sea, so that the sea clock could be set accurately before a ship left port, but he found that H4 worked far better than expected and made the heavy sea clock unnecessary.

How John Harrison Won His Reward

The terms of the prize were that the timepiece should be sent on a voyage to the West Indies (a regular route at the time of the slave trade), and the amount of the award would depend on the degree of accuracy of the clock or watch. The full £20,000 would be paid if the longitude obtained was correct to within 30 miles, but if this was only 60 miles the prize would reduce to £10,000.

When tested in 1761, the watch lost only 5.1 seconds over the 81 days of the round voyage, although this figure was arrived at by making an allowance, or “rate”, for the known performance of the timepiece over that length of time. Unfortunately, this was not made clear by Harrison at the outset, and the discrepancy nullified the trial. As a result, he was only awarded £2,500, and this would only be paid if the result was confirmed by a second trial.

This second trial took place in 1764, with a gain of one second per day. On the outer voyage of 47 days, the watch allowed computation of the longitude to within 10 miles, which was three times better than the maximum requirement of the test and should have been enough to land Harrison the full £20,000 prize.

However, the Board of Navigation refused to believe that the watch was that accurate and made all sorts of stipulations before they would agree to hand over the money. Harrison was required to make two more watches, and to hand over the original watch so that it could be dismantled and examined by a committee. If an independent craftsman could replicate the watch, Harrison would be awarded the balance of £10,000, with the remaining £10,000 only being payable if the two extra watches were produced.

When the committee met in August 1765 and examined the H4 watch in Harrison’s presence they were sufficiently impressed to pay him the money, but it was still only half of what had originally been promised. Harrison was determined to win the full amount.

When H4 was copied by a master watchmaker, Larcum Kendall, in 1769, it was found to be of such excellent craftsmanship that it was taken by Captain Cook on his second and third voyages of discovery and used to map the South Pacific Ocean.

Before Harrison could produce another watch, mariners were able to make full use of another invention, namely the sextant, which could be used to make much more accurate calculations of local time and thus render the rival lunar distance method more workable. Harrison therefore had to produce something that was even more accurate than H4, and he was not even allowed access to his own invention when building the new watch, which was labelled H5.

In order to get H5 tested, and to claim the rest of the £20,000, Harrison was forced to appeal to the King, and in 1772 H5 was tested by the Royal Observatory and found to keep time to within a third of a second a day. Nevertheless, the Board refused to acknowledge the test and it was only when Harrison appealed to Prime Minister (Lord North), and a further Act of Parliament was passed in 1773, that the full prize was finally awarded.

However, Harrison was by now an old man, and he only had three years left in which to bask in the recognition that he so fully deserved. He died in 1776 on what was believed to be his 83rd birthday.

One has to suppose that the Board of Navigation never really believed that anyone would meet the full terms of the prize, which had been unclaimed since 1714, and was always going to be reluctant to award it to a man whose background was in joinery and was, to all intents and purposes, an amateur when in came to clocks and watches. However, John Harrison was an extremely clever and inventive man who was prepared to spend many years on getting something as good as he could get it.

One innovation that Harrison incorporated was the bimetallic strip, being a strip of two metals fixed together such that changes in temperature would be compensated due to the different expansion coefficients of the two metals. This is the principle used in many later inventions, including the electric toaster. In clocks and watches, the mechanism will not be subject to warping as the temperature rises and falls, thus affecting the accuracy of the timepiece.

The modern marine chronometer, developed from Harrison’s watches, enabled the British Navy to explore and chart the world’s oceans for the next 200 years, and helped Great Britain to become a major world power due to its dominance of the seas.

Of course, the advent of satellites has revolutionised navigation and made much of Harrison’s work redundant. That should not, however, diminish the credit that Harrison deserved. Countless lives must have been saved thanks to his hard work and dedication.

The H5 Chronometer
The H5 Chronometer | Source


    0 of 8192 characters used
    Post Comment
    • profile image

      Milind Paranjpe 

      2 years ago

      Great !

      Well written. I read the 'Longitude' by Ms Dava Sobel, a book every maritime library must keep.



    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)