NOVA Online | Lost at Sea: The Search for Longitude
The history of longitude is a record of the effort, by astronomers, cartographers and navigators Finding an accurate and reliable method of determining longitude took Determining longitude at sea was also much harder than on land. that for want thereof many Ships have been retarded in their voyages, and many lost. Longitude is the measurement east or west of the prime meridian. Online Courses · Educator Network · Grants for Educators It is the basis for the International Date Line. Coordinates can be used to locate any point on Earth. Map Match Game · PBS: Nova: Lost at Sea—The Search for Longitude. rozamira.info: NOVA: Lost at Sea - The Search for Longitude., nova: Movies Not Rated; Studio: PBS; DVD Release Date: January 15, ; Run Time:
Harrison was a man of many skills and he used these to systematically improve the performance of the pendulum clock. He invented the gridiron pendulum, consisting of alternating brass and iron rods assembled so that the thermal expansions and contractions essentially cancel each other out. Another example of his inventive genius was the grasshopper escapement — a control device for the step-by-step release of a clock's driving power.
Developed from the anchor escapementit was almost frictionlessrequiring no lubrication because the pallets were made from wood. This was an important advantage at a time when lubricants and their degradation were little understood. In his earlier work on sea clocks, Harrison was continually assisted, both financially and in many other ways, by George Grahamthe watchmaker and instrument maker. This support was important to Harrison, as he was supposed to have found it difficult to communicate his ideas in a coherent manner.
Longitude problem[ edit ] This section includes a list of referencesrelated reading or external linksbut its sources remain unclear because it lacks inline citations. April See also: History of longitude and Longitude rewards Longitude lines on the globe Longitude fixes the location of a place on Earth east or west of a north-south line called the prime meridian. Knowledge of a ship's east-west position was essential when approaching land.
After a long voyage, cumulative errors in dead reckoning frequently led to shipwrecks and a great loss of life. Avoiding such disasters became vital in Harrison's lifetime, in an era when trade and navigation were increasing dramatically around the world. Many ideas were proposed for how to determine longitude during a sea voyage. Earlier methods attempted to compare local time with the known time at a reference place, such as Greenwich or Parisbased on a simple theory that had been first proposed by Gemma Frisius.
The methods relied on astronomical observations that were themselves reliant on the predictable nature of the motions of different heavenly bodies. Such methods were problematic because of the difficulty in accurately estimating the time at the reference place.
Harrison set out to solve the problem directly, by producing a reliable clock that could keep the time of the reference place. His difficulty was in producing a clock that was not affected by variations in temperaturepressure or humidityremained accurate over long time intervals, resisted corrosion in salt air, and was able to function on board a constantly-moving ship.
Many scientists, including Isaac Newton and Christiaan Huygensdoubted that such a clock could ever be built and favoured other methods for reckoning longitude, such as the method of lunar distances. Huygens ran trials using both a pendulum and a spiral balance spring clock as methods of determining longitude, with both types producing inconsistent results. Newton observed that "a good watch may serve to keep a reckoning at sea for some days and to know the time of a celestial observation; and for this end a good Jewel may suffice till a better sort of watch can be found out.
But when longitude at sea is lost, it cannot be found again by any watch". The first three marine timekeepers[ edit ] In the s, the English clockmaker Henry Sully invented a marine clock that was designed to determine longitude: Very unconventionally, the balance oscillations were controlled by a weight at the end of a pivoted horizontal lever attached to the balance by a cord. This solution avoided temperature error due to thermal expansiona problem which affects steel balance springs.
Sully's clock only kept accurate time in calm weather, because the balance oscillations were affected by the pitching and rolling of the ship.
However his clocks were amongst the first serious attempts to find longitude in this way. Harrison's machines, though much larger, are of similar layout: H3 has a vertically mounted balance wheel and is linked to another wheel of the same size, an arrangement that eliminates problems arising from the ship's motion.
He presented his ideas to Edmond Halleythe Astronomer Royalwho in turn referred him to George Grahamthe country's foremost clockmaker. Graham must have been impressed by Harrison's ideas, for he loaned him money to build a model of his "Sea clock".
As the clock was an attempt to make a seagoing version of his wooden pendulum clocks, which performed exceptionally well, he used wooden wheels, roller pinions and a version of the 'grasshopper' escapement. Instead of a pendulum, he used two dumbbell balances, linked together. It took Harrison five years to build his first sea clock or H1.
History of longitude - Wikipedia
The clock was the first proposal that the Board considered to be worthy of a sea trial. The clock lost time on the outward voyage. However, it performed well on the return trip: The master noted that his own calculations had placed the ship sixty miles east of its true landfall which had been correctly predicted by Harrison using H1. Harrison had moved to London by  and went on to develop H2,  a more compact and rugged version.
Inafter three years of building and two of on-land testing, H2 was ready, but by then Britain was at war with Spain in the War of Austrian Succession and the mechanism was deemed too important to risk falling into Spanish hands.
- John Harrison
In any event, Harrison suddenly abandoned all work on this second machine when he discovered a serious design flaw in the concept of the bar balances. He had not recognized that the period of oscillation of the bar balances could be affected by the yawing action of the ship when the ship turned such as ' coming about ' while tacking. It was this that led him to adopt circular balances in the Third Sea Clock H3. The problem was that, because Harrison did not fully understand the physics behind the springs used to control the balance wheels, the timing of the wheels was not isochronous, a characteristic that affected its accuracy.
The engineering world was not to fully understand the properties of springs for such applications for another two centuries. Certainly in this machine Harrison left the world two enduring legacies — the bimetallic strip and the caged roller bearing. The longitude watches[ edit ] After steadfastly pursuing various methods during thirty years of experimentation, Harrison found to his surprise that some of the watches made by Graham's successor Thomas Mudge kept time just as accurately as his huge sea clocks[ citation needed ].
It is possible that Mudge was able to do this after the early s thanks to the availability of the new "Huntsman" or "Crucible" steel produced by Benjamin Huntsman sometime in the early s which enabled harder pinions but more importantly, a tougher and more highly polished cylinder escapement to be produced. He proceeded to redesign the concept of the watch as a timekeeping device, basing his design on sound scientific principles.
The "Jefferys" watch[ edit ] He had already in the early s designed a precision watch for his own personal use, which was made for him by the watchmaker John Jefferys c. This watch incorporated a novel frictional rest escapement and was not only the first to have a compensation for temperature variations but also contained the first miniature 'going fusee' of Harrison's design which enabled the watch to continue running whilst being wound.
These features led to the very successful performance of the "Jefferys" watch, which Harrison incorporated into the design of two new timekeepers which he proposed to build. This was known as running down a westing if westbound, or easting if eastbound. Determining latitude was relatively easy in that it could be found from the altitude of the sun at noon with the aid of a table giving the sun's declination for the day.
Latitude can also be determined from night sightings of Polaristhe northern pole star. However, since Polaris is not precisely at the pole, it can only provide accurate information if the precise time is known or many measurements are made over time, which made developing an accurate chronometer for long ocean voyages even more vital.
Navigating purely by latitude was of course vulnerable if the sun was clouded over at noon, and caused problems as it prevented ships from taking the most direct route, a great circleor a route with the most favourable winds and currents, extending voyages by days or even weeks.
This increased the likelihood of short rations,  scurvy or starvation leading to poor health or even death for members of the crew and resultant risk to the ship. Errors in navigation also resulted in shipwrecks.
TLS Cipher Negotiation Error Page
Motivated by a number of maritime disasters attributable to serious errors in reckoning position at sea, particularly spectacular disasters such as the Scilly naval disaster of which took Admiral Sir Cloudesley Shovell and four ships of his fleet, the British government established the Board of Longitude in Each prize, in increasing amounts, was for solutions of increasing accuracy.
These prizes, worth millions of dollars in today's currency, motivated many to search for a solution. Harrison built five, two of which were tested at sea. His first, H-1, was not tested under the conditions that were required by the Board of Longitude.
Instead, the Admiralty required that it travel to Lisbon and back. It lost considerable time on the outward voyage but performed excellently on the return leg, which was not part of the official trial.
The perfectionist in Harrison prevented him from sending it on the required trial to the West Indies and in any case it was regarded as too large and impractical for service use. He instead embarked on the construction of H This chronometer never went to sea, and was immediately followed by H During construction of H-3, Harrison realised that the loss of time of the H-1 on the Lisbon outward voyage was due to the mechanism losing time every time the ship came about while tacking down the English Channel.
Harrison produced H-4, with a completely different mechanism which did get its sea trial and satisfied all the requirements for the Longitude Prize.Lost at Sea the search for longitude part 5 of 6
However, he was not awarded the prize and was forced to fight for his reward. Though the British Parliament rewarded John Harrison for his marine chronometer inhis chronometers were not to become standard. Chronometers such as those by Thomas Earnshaw were suitable for general nautical use by the middle of the 19th century The lunar distance method was initially labour-intensive because of the time-consuming complexity of the calculations for the Moon's position.
Early trials of the method could involve four hours of effort. Between and earlier in British and French navigation practice, later in American, Russian, and other maritime countriesaffordable, reliable marine chronometers became available, with a trend to replace the method of lunars as soon as they could reach the market in large numbers.
It became possible to buy three or more chronometers, serving for checking on each other redundancyalthough according to Nathaniel Bowditch, their use was precluded because they were very expensive,  obviously much higher than a single sextant of sufficient quality for lunar distance navigation which continued in use until Three chronometers provided triple modular redundancyallowing error correction if one of the three was wrong, so the pilot would take the average of the two with closer readings average precision vote.
There is an old adage to this effect, stating: Nonetheless, expert navigators continued to learn lunars as late asthough for most this was a textbook exercise since they were a requirement for certain licenses. They also continued in use in land exploration and mapping where chronometers could not be kept secure in harsh conditions. The British Nautical Almanac published lunar distance tables until and the instructions until The development of wireless telegraph time signals in the early 20th century, used in combination with marine chronometers, put a final end to the use of lunar distance tables.
This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. December Learn how and when to remove this template message Telegraph signals were used regularly for time coordination by the United States Naval Observatory starting in Another regular broadcast began in Halifax, Nova Scotia inand time signals that became more widely used were broadcast from the Eiffel Tower starting in This method drastically reduced the importance of lunars as a means of verifying chronometers.
Modern sailors have a number of choices for determining accurate positional information, including radar and the Global Positioning System, commonly known as GPSa satellite navigation system. With technical refinements that make position fixes accurate to within meters, the radio-based LORAN system was used in the late 20th Century but has been discontinued in North America.
History of longitude
Combining independent methods is used as a way to improve the accuracy of position fixes. Even with the availability of multiple modern methods of determining longitude, a marine chronometer and sextant are routinely carried as a backup system. Further refinements for longitude on land[ edit ] Main article: Geodesy For the determination of longitude on land, the preferred method became exchanges of chronometers between observatories to accurately determine the differences in local times in conjunction with observation of the transit of stars across the meridian.
An alternative method was the simultaneous observation of occultations of stars at different observatories. Since the event occurred at a known time, it provided an accurate means of determining longitude. In some cases, special expeditions were mounted to observe a special occultation or eclipse to determine the longitude of a location without a permanent observatory. From the midth century, telegraph signalling allowed more precisely synchronization of star observations.
This significantly improved longitude measurement accuracy. The Royal Observatory in Greenwich and the U. Coast Survey coordinated European and North American longitude measurement campaigns in the s and s, resulting in improved map accuracy and navigation safety.
Synchronization by radio followed in the early 20th century. In the s, the use of satellites was developed to more precisely measure geographic coordinates GPS. Notable scientific contributions[ edit ] In the process of searching for a solution to the problem of determining longitude, many scientists added to the knowledge of astronomy and physics.