The Longitude Problem and John Harrison

John Harrison

John Harrison is known for receiving a UK Parliament award for his chronometer. The importance of his invention was that it was suitable for use at sea and thus helped navigators of the time to precisely determine Longitude. The H5, Harrison’s fifth attempt at a marine timekeeper, was precise to a tenth of a second per day, which is very impressive even by today’s standards. But let’s take things from the start...ish...

During the seventeenth and eighteenth centuries, development of navigation instruments was encouraged, since seafaring was used more and more for trading and was the only means of exploring. Navigation by definition is the science of ascertaining one’s position, and subsequently plotting and following a course. Latitude - how many degrees North or South someone is positioned from the equator - could be determined easily within the accuracy of a degree, by means of measuring the altitude of celestial bodies using a sextant, an astrolabe or other instruments.

Longitude on the other hand was not as easy to be determined. The theory was there though: The earth needs twenty-four hours to perform one complete revolution around its axis. Therefore it rotates fifteen degrees per hour. So for example, if I know that it is 12:00 (noon) at a given location, but where I’m at is still 11:00, then I’m fifteen degrees away from the former location. Sailors could estimate the current time by observing the sun’s position but had great difficulty knowing the time of a reference location – in this case the reference location was Greenwich.

King Charles II founded the Greenwich Royal Observatory (1675) for this exact reason. Tables of the position of the moon relative to the stars where compiled, in order to help sailors estimate the time at Greenwich, but the method was inaccurate. So in 1714, the Parliament approved the Governments request for awarding £20,000 pounds to the person who would find a way to estimate Longitude within an accuracy of half a degree. Even a “Board of Longitude” was formed, in order to review and evaluate the contestants and their inventions.

John Harrison – 21 at the time – was a self-taught clock maker and repairer. He would even improve designs and mechanisms of clocks taken to him for repair.

By 1728, he had enough drawings and full scale models of parts of his proposed solution, so he headed to London to seek financial assistance. He was advised to see George Graham, who was at the time the master of the Clockmakers Company. Graham was impressed enough to loan Harrison money from his personal fund to help him develop his idea.   

Sometime between 1730 and 1735, Harrison finished his first marine timekeeper.

Harrison's H1

The H1 was a heavy, weird looking clock which had to be wound every day, as opposed to the wooden clocks of the day that had an eight day power reserve. It did not use a pendulum, but a balance mechanism which would compensate any change in motion, therefore minimizing the effects of the direction of gravity. It was accurate to three seconds a day. In 1736, H1 and its maker travelled by sea to Lisbon and back so the timekeeper would be tested under the circumstances it was designed for. The H1 was good enough to correct the Longitude readings on the way back but Harrison requested from the board of Longitude more money in order to proceed in creating a second marine timekeeper. After working on the second incarnation (H2) of the timekeeper for about 4 years, he discovered that the design of the bar balances used to compensate a ship’s rocking motion was flawed. He then proceeded with his third attempt. It took 19 years for H3 to materialize. It failed to reach the accuracy demanded, and even though it was smaller and lighter than its predecessors, it was still a cumbersome clock, and impractical to adjust. It was important for two of its parts though: the bimetallic strip, and roller bearings. They were designed to compensate for changes in temperature and to minimize friction on the movement respectively, and they were innovations that found their way in all sorts of machinery and mechanisms thereafter. After finishing the H3, Harrison was convinced that a large clock would not be suitable for the purpose.

H2 and H3

H4

Enter the H4. It was a watch instead of a clock, albeit a big one since it was about 13cm in diameter. William, John’s son, travelled with this watch to Jamaica aboard the ship Deptford, and after the two months it took them to get there, the H4 was only an impressive 5.1 seconds slow. A second trip followed with an error of 39.2 seconds over 47 days. That was three times better than the accuracy requested by the board. Despite this accuracy, the board insisted that the watch was a fluke and that copies of it should be made and tested. They would award Harrison with half the prize money when he submitted his timekeepers along with all his ‘secrets’, and the rest when accurate copies of H4 would be made. Needless to say that was not what Harrison wanted, but the board must have been very determined since in 1765 all four timekeepers were submitted. Larcum Kendall was also appointed to copy H4. Now the board wanted Harrison to make two more copies of H4 in order to award him the second half of the prize money. John and son started working on a fifth timekeeper (H5) while Kendall worked on his copy of the H4, the K1. The board though insisted that both copies should be made by the Harrisons, and would not regard H5 and K1 as the two copies of H4. Even after H5 met the approval of King George III, the Harrison’s had to petition Parliament to receive an amount of £8750 in 1773. The significance of course is the recognition that John Harrison solved the Longitude problem.

H5

It is important to say that Kendall’s K1 was used and enthusiastically approved by Captain James Cook. It confirmed that a marine timekeeper was the best and most accurate way of determining Longitude.

Η1, Η2, Η3 & Η4 are now kept at the National Maritime Museum (Greenwich, London) and the H5 is at the Clockmaker’s Museum at Guildhall, London.