Pictures of clock by Jeff Darken
What is it? It is a longcase clock, dated 1727, by John and James Harrison. It has a black japanned case with floral decoration and a movement made mostly of wood. It is the second in a series of three timekeepers made for research purposes. John Harrison called them "precision pendulum clocks".
Who was John Harrison? He lived from 1693 to 1776, a joiner, self-taught clockmaker and scientist, a Copley Medallist of the Royal Society, and winner of the Longitude Prize. He was born in West Yorkshire, on the Nostell Priory Estate, where his father was the estate carpenter.
He lived for a time, as a boy, and some of his adulthood, in North Lincolnshire, Barrow-upon-Humber, when the family moved there. From about the age of 40 until his death he lived in London. John Harrison has a memorial in Westminster Abbey. He may not be a household name, but Neil Armstrong is, and there is a connection between them. In the early 1970s, at a dinner where he was the honoured guest at 10 Downing Street, Neil Armstrong proposed a toast to John Harrison. His invention, his extremely accurate timekeepers, Armstrong said, enabled men to explore the Earth with precision and, when most of the Earth had been explored, to dare to build navigation systems for voyages to the Moon. He said “You, ladies and gentlemen, started us on our trip.”
|John Harrison's memorial in Westminster Abbey, London, was dedicated on 24 March 2006. Through the dedication stone is a bimetallic strip, representing one of Harrison's key inventions. The strip is aligned to, and marked with, the meridian that runs through the stone, 000 degrees, 07 minutes, 35 seconds West.|
Image: PR Hastings
Why is this clock on the BBC History of the World website? Precision pendulum clock No. 2 is a fundamental part of the story of John Harrison’s relentless quest to develop a practical method of determining longitude at sea using the time difference principle. It boils down to “Where on Earth are we?” By having a reliable timekeeper set to the time at a known longitude, for example, a ship's home port, and comparing this to local time, which can be accurately determined by observation of the sun and stars, the time difference can then be converted to an east or west distance from the fixed geographical point that the timekeeper represents. This clock was made in response to The Longitude Act of 1714, and with it Harrison achieved extraordinarily accurate timekeeping on land, a second a month, something never achieved before. After the precision pendulum clock series Harrison set about making a portable version, H1, the world's first workable marine timekeeper. Its movement is recognisably an evolution from the precision pendulum clocks, and a surprising amount of the movement is made of oak and lignum vitae. H1 is truly a stablemate of the precision pendulum clocks. Not only are their movements similar, H1 was also made in the same workshop, in Barrow-upon-Humber. The eventual outcome of Harrison's research and development work was H4, his masterpiece, and the acknowledged winner of the Longitude Prize. H4 has been called the most important timekeeper ever made. This was a great feat of engineering and technology, thought to be impossible by many of the greatest scientists of the 18th century, including Sir Isaac Newton. John Harrison proved with his timekeepers that an engineering solution to determining time difference was not only possible, but in fact was also the most practical method for mariners to determine longitude.
What is time difference? 15 degrees of longitude equals 1 hour's time difference. If it is 12 noon here, 15 degrees east it is 1 pm, and 15 degrees west it is 11 am. In a sense, the Earth itself is a clock. There are 24 hours in a day, the time needed for the sun to reach each mid-day, and there are 360 degrees around the Earth's circumference. 360 divided into 24 parts is 15. The earth turns at a uniform rate, and mid-day, when the sun is at its highest, is always on the move, from east to west. The fixed reference point is not a place, but a time, from which a time difference can be determined, and from that a distance, or position can be fixed. Let us suppose that we are on a ship somewhere in the Gulf of Mexico. We have accurately determined our latitude with a sextant by measuring the elevation of the sun. But we have not yet fixed our position because we do not know the longitude. It is coming up to mid-day and we can set the ship’s clock because we can very accurately tell when the sun is at its highest. At exactly mid-day we check the local time against the marine chronometer with the time back at homeport, say London. The chronometer tells us that it is 6 pm there. This is 6 hours time difference, which at 15 degrees for every hour means that we are 90 degrees west of London. We have fixed our position, and with that foreknowledge can make our landfall with as much safety and certainty as is possible. It was not having this foreknowledge, often combined with poor maps, that was causing problems for all maritime nations, and for Britain with its global ambitions it was a very major problem indeed. The British government set up a sort of competition, the Longitude Act, for the “practicable solution to finding the Longitude at sea”. What was the Longitude Act? It was an Act of Parliament in 1714 that offered a huge cash prize for whoever came up with the practical solution to determining longitude at sea. In effect it set the terms and conditions of what can be considered to be the first government sponsored research and development project. Not being able to determine longitude meant, effectively, that you were lost, or too uncertain of exact position, and being lost at sea can have extremely serious consequences. Time lost through inefficient sailing, because of navigational errors, could easily turn into a big problem, and disaster, as supplies ran out, and crew succumbing to illness and death as a result from scurvy, starvation, and foul water. Navigational errors could also lead to running out of "sea room". The zig zag of tacking in order to reach the right landfall had to be planned in order to not run into a lee shore, or some other obstacle. As simple a thing as not being able to accurately determine longitude was costing a fortune in lives, ships and cargoes lost, hence the size of the prize, £20,000, perhaps £10 million today.
Were there any other methods being looked into? Yes. Most scientists thought the answer lay in astronomy, the positions of planets and moons, and in response to the opinions of scientists and astronomers observatories were built in many of the great European cities to map the skies. Few scientists, including Sir Isaac Newton, thought a sufficiently accurate timekeeper was possible, so that when a country carpenter, Harrison, set about developing timekeepers to determine longitude at sea, there was a lot of skepticism, particularly from the Board of Longitude, many of whom were astronomers. Harrison did have the backing of the Royal Society, however, and that support was very important.
What made Harrison's precision pendulum-clocks so accurate? The movements of his early clocks were made mostly of wood, oak, boxwood and lignum vitae. The use of wood is unusual but, in many senses, incidental. He and his brother James were joiners and wood was their starting point. Pendulum clocks were the most accurate clocks at that time and Harrison set about isolating every factor that affected their performance and designing a way around the problem. Lubricants were extremely variable in quality and were often the cause of clocks being unreliable. His clocks require no added lubrication because he minimized friction. He did this with his invention of the double-thrust or grasshopper escapement, which eliminated sliding friction. He further reduced friction by introducing roller pinions, rolling friction instead of sliding friction. The roller pinions, and other components that came into moving contact were made of lignum vitae, an extremely dense and waxy wood, so waxy that its surface is very slippery. In effect these parts were self-lubricating. The other main problem was temperature. A conventional pendulum will become longer as temperature rises because of expansion of the metal; the opposite is true as temperature falls. Changes in the pendulum's length will completely throw off accurate timekeeping, and hence its regulation, or reliability. Harrison invented the temperature-compensating, or grid-iron, pendulum, an arrangement of brass and steel rods, an arrangement whose length stayed the same regardless of temperature.
How did Harrison win the Longitude Prize? His first sea-clock H1 went on a sea-trial to Lisbon and showed a lot of promise, so clearly Harrison, the Royal Society and the Board of Longitude thought he was on to something. Harrison kept working on developing large sea-clocks, but they did not achieve the accuracy and reliability he and the Act required at least not for the big prize. After H1 there were two more large sea-clocks, called H2 and H3, and he spent over two decades working on them. Harrison's efforts in developing the sea-clocks were supported by advances from the Board of Longitude. By this time Harrison was also a full time clock and watch maker, and very much integrated into the horological trade in London, by far the most significant and vibrant in the world at that time. Whilst not belittling Harrison's achievements, he was not a lone genius, although he was very radical in his thinking and problem-solving abilities, as made amply clear in Dava Sobel's very worthy bestselling book "Longitude" about Harrison and the longitude problem, and in the excellent little book "Harrison" written by Jonathan Betts of the NMM. Then in 1753 came Harrison’s great breakthrough when the small pocket watches he was also designing achieved a far greater accuracy then even he thought possible. To say he was barking up the wrong tree is not really true, because he had learned so much with all the previous work. H4 was the result, it looks like a very large pocket watch, but inside bristles with new technology, including the use of diamonds, for friction reduction, something Harrison pioneered. The key though was a high energy, fast-moving balance wheel, or oscillator, which, with its temperature compensation mechanism, regulated the movement and made the watch stable and accurate. Sea trials to Barbados proved H4's accuracy and reliability. Harrison was eventually awarded the prize but it took Royal intervention, a direct appeal by Harrison to the monarch, and a further act of parliament because of intransigence on the part of the Board of Longitude. "By God, Harrison, I shall see you righted" it is recorded the King said. From accounts of the time the exchanges between Harrison and the Board were often acrimonious, and Harrison was probably not the easiest man to get along with. Also, it is very important to understand that by this time the other main contender to finding longitude at sea, the lunar distance method, was also proving to be a viable method. From the Board's point of view they were being very careful with public money.
What is the lunar distance method? It is another method of determining time difference, but without a clock. Navigators still needed to figure out what time it was in Greenwich at the time of their lunar observation, however. The method relied on the compilation of much data collected at the Royal Observatory. It also relies on the relatively quick movement of the moon across the background sky, completing a circuit of 360 degrees in 27.3 days. In an hour then, it will move about half a degree, roughly its own diameter, with respect to the background stars and the Sun. Using a sextant, the navigator precisely measures the angle between the moon and another body. That could be the Sun or one of a selected group of bright stars lying close to the Moon's path. At that moment, anyone on the surface of the earth who can see the same two bodies will observe the same angle, after correcting for the parallax error which will inevitably result if the lunar observation is taken anywhere but the latitude of Greenwich (where the lunar distance table was compiled). The navigator then consults a prepared table of lunar distances and the times at which they will occur, the Nautical Almanac created by the Astronomer Royal and the Royal Observatory. By comparing the corrected lunar distance with the tabulated values, the navigator finds the Greenwich time for that observation. Knowing Greenwich time and local time, the navigator can work out longitude, readily calculated from the time difference between Greenwich time and local time. Local time can be determined from a sextant observation of the altitude of the Sun or a star. Whilst it is a viable and useful method it does have drawbacks. It may not be possible because of weather to make an observation, and in any event the pitching deck of a ship will always make "taking a lunar" tricky. The moon cannot be seen for a number of days each month. The person doing the observation and calculations, which all took a number of hours, really had to be well trained and do their work, and calculations, with great precision to get an accurate result. In comparison the timekeeping method is very simple and quick, but relied totally on precision timekeeping. John Harrison's overarching achievement was proving that an engineering solution was the most practical method. In the end, however, the Board of Longitude, for its investments in money to fund Harrison's research, and support to the Astronomer Royal in the compilation of the lunar distance tables, got two viable solutions to the longitude problem. In practice a chronometer was used most of the time. But when there was an opportunity to "take a lunar", if it was thought necessary, it would be done. This way the accuracy of the timekeeper could be monitored and re-calibrated if necessary.
How quickly did this new method of navigating get taken up? Captain James Cook, like John Harrison a Copley Medallist of the Royal Society (and another Yorkshireman!), took an exact copy of H4, called K1, made by Larcum Kendall, with him on his 2nd voyage of discovery 1772-75, at the request of the Astronomer Royal, Reverend Neville Maskelyne, and the Board of Longitude. This was for the purposes of an extensive field test, and to see if someone else could duplicate what Harrison had achieved. It would have been a most exacting and demanding field test too, because Captain James Cook was the greatest navigator of the latter half of the 18th century, and commanded huge respect within the Royal Navy, and more widely amongst scientific, maritime and naval peers of Britain and other countries, even those that Britain was at war with, like the French. Safe passage for Cook's scientific expeditions was assured. Such is Cook's reputation that even amongst explorers of today's world the influence and inspiration of one Yorkshire's greatest sons is still there. One of the space shuttle fleet, the Endeavour, for example, is named after Captain Cook's ship.
But in 1772, seven years after tacit acknowledgement of Harrison's achievement by the Board of Longitude, and a further financial reward for it, following the intervention of the King and Parliament, there were still suspicions that H4 was a fluke. Captain James Cook, who had been trained with the lunar distance method of determining longitude, was converted in this voyage to the timekeeping method of determining longitude. His increasing appreciation of this technical innovation can be seen in the log he kept of the voyage "our Trusty Friend, the Watch". When they arrived back at Plymouth after nearly 3 years at sea the longitude indicated by K1 was within 5 miles of the known longitude of Plymouth. There would have been opportunties for periodic calibrations against known longitudes (determined for example by a lunar distance calculation) but it was nevertheless an incredible result, and a vindication of Harrison's efforts. Cook’s stamp of approval carried a lot of weight with the Board of Longitude, The Royal Society, and The Admiralty, and it had the effect of getting London's horological trade focused on studying Harrison's designs, and then reducing the cost of marine timekeepers, so that by the early 19th century they were in widespread usage until GPS started being commonly used in the 1980s. Even today, though, chronometers are still kept and maintained on ships as a back-up means of navigation. John Harrison died less than a year after Cook's return, but no doubt learned of the triumph of his timekeeper design. The approval of someone of Cook's stature and prominence, another Copley Medallist, would have meant a lot to Harrison. Captain Cook did not have many more long sea voyages. Sadly he was murdered by natives in Hawaii, on 14 February 1779 during his third voyage of discovery, but he never went to sea again after his 2nd voyage of discovery without a "Watch", known in modern times as a ship's chronometer.
Cook, in fact, during his first voyage of discovery already had, perhaps unknowingly, some exposure to John Harrison's technology. In June 1769 Cook was on the island of Tahiti to observe a transit of Venus with a special kind of telescope, that could track the transit. The telescope was attached to an "astronomical clock" that featured a grid-iron pendulum, something Harrison had invented over 40 years earlier.
|Captain James Cook was the greatest navigator and explorer|
of the 18th century
What is John Harrison’s legacy? Some of the progenies of Harrison’s inventions are with us today, for example bi-metallic strips, commonly used in thermostats, and caged ball bearings, whose pre-cursor is the caged roller bearing. Harrison also pioneered the use of diamonds as anti-friction devices, the forerunner of jewelled bearings in precision watches, and other applications. These are all fundamental bits of technology that are in common usage in countless machines. Harrison was not only a brilliant man, he was a truly great man too. He did not travel much in his life but he was on an intellectual journey to achieve precision timekeeping. His journey started as a carpenter/joiner, but he became a clockmaker, an engineer, and ended up, in effect, a materials scientist long before such a profession was recognised. Harrison used his intellect and determination to solve the most intractable scientific problem of the 18th century. With his timekeepers he made an exploratory foray into the infinite ocean of space-time and he found a way forward. He used time, the fourth dimension, to fix points in three-dimensional space, and his solution, and the engineering innovations he invented, have had widespread and incalculable benefits for all humanity. It is not an exaggeration to say that John Harrison was a clockmaker who changed the world.
The way we navigate now with the Global Positioning System (GPS) and satellite navigation, how does it differ from using chronometers and sextants? It is still timekeeping at the heart of GPS. GPS uses satellites with atomic clocks, and receivers that calculate distance because of the time difference between the signal’s being sent and its being received. With signals from three different satellites, the relative positions of which to their ground stations is known, the position of the receiver is triangulated, i.e. its position has been determined. GPS is like positional astronomy, except that in the case of GPS the "stars" are man-made, they are placed where they are wanted, and they broadcast signals that carry current location and time information (which means, unlike positional astronomy, they do not have to be found). It still comes down to precision timekeeping, and time difference, to fix location. In fact positional astronomy, navigation, the uniform rotation of the earth, precision timekeeping, and the development of star charts and terrestrial maps are all inextricably linked.
Global Positioning System, a description
It is planned to create a new permanent display about John Harrison and the Longitude problem around this clock at the Leeds City Museum.
The Board of Longitude Project
The National Maritime Museum, The University of Cambridge, and The Arts and Humanities Research Council are taking forward a research project about the Board of Longitude. During 2014 there will a conference and publications presenting for the first time a comprehensive history of the Board of Longitude:
Addendum, 14/06/2013, course set, second star to the right, and straight on 'til morning.... target date January 2014, in good time for the tercentenary year of the Longitude Act of 1714.
Second star to the right, and straight on 'til morning
Posted by Ian Fraser
For more information about John Harrison, the Longitude problem, navigation, etc. please explore the links below:
The National Maritime Museum, Greenwich
Positional astronomy, an explanation: http://www.nmm.ac.uk/explore/astronomy-and-time/astronomy-facts/instruments/positional-astronomy
Something about the Royal Observatory, Greenwich: http://en.wikipedia.org/wiki/Royal_Observatory,_Greenwich
A History of the World, link to objects from museums in Leeds: http://news.bbc.co.uk/local/leeds/hi/people_and_places/history/newsid_8353000/8353063.stm
The Science Museum in London has one of John Harrison's earliest clocks: http://www.makingthemodernworld.org.uk/icons_of_invention/technology/1750-1820/IC.021/
The same Science Museum website has a very good overview of the problems of navigation and the technologies developed to navigate and make maps http://www.makingthemodernworld.org.uk/stories/enlightenment_and_measurement/01.ST.06/?scene=5
BBC documentary about John Harrison and the clock at Leeds, "The Clock That Changed the World" can be seen on Youtube:
And a Yorkshire Post article: http://www.adam-hart-davis.org/articles/yorkshire%20post%2013%20may%202010.pdf
Some current information about the works being undertaken to H2: http://www.nmm.ac.uk/blogs/collections/2010/07/research_on_harrisons_second_t.html http://www.nmm.ac.uk/blogs/collections/2010/07/research_on_harrisons_second_t.html
The Worshipful Company of Clockmakers have a lot of Harrison material, including precision pendulum clock No. 3, and H5, plus numerous manuscripts written by Harrison: http://www.clockmakers.org/?page_id=1554
This link will take you to a recent paper on Harrison's pioneering use of diamond in H4: http://www.smf.phy.cam.ac.uk/fsp/Publications/Friction%20papers/573FrictHirdAS65.pdf
New links about the Board of Longitude project:
Archive papers of the Board of Longitude
Guardian article about digitisation of the archives of the Board of Longitude