Pierre, having some small skill in astronomy, and made an interest with a French lady, then in Favour at the Court, proposed no less than the discovery of Longitude. They too were based on the position of the Moon.
Based on his own observations, he had been able to show that the best available star catalogue, that of Tycho Brahe, was prone to errors, which meant that any longitude found could be in error by up to several hundred miles. To provide the necessary data, he said, would require years of observation with large instruments fitted with telescopic sights.
He explained how observations of Io in had shown that the difference in Longitude between Greenwich and Hoai-gnan, a city on the east coast of China was about 10 degrees or miles less than had been previously thought.
For the first 14 years, there was almost no progress, for although Flamsteed had been provided with a range of instruments; none was up to the job. It was only when he came into money following the death of his father that any real progress was made. The first recorded observation was taken in and the last shortly before he died in With it, he obtained most of the data needed for his catalogue of 2, stars, which was published posthumously in Although errors were subsequently discovered, it was of sufficient accuracy to be of use to those seeking to navigate by the lunar-distance method.
The setting up of the Board of Longitude With the lunar-distance method still far from being perfected, the British Government in , set up the Board of Longitude.
The pull of the Sun speeds the Moon as it moves towards it and slows it as it moves away. Although the Moon comes back to approximately the same position in the sky from one month to the next, the exact path it follows varies. Try as they might, astronomers and mathematicians had been unable to adequately model the orbit.
Halley therefore decided to observe the Moon over the period of a complete Saros cycle, a little over 18 years and the time taken for the Earth Sun and Moon to return to approximately the same geometry, and use this data to create his lunar tables. When the tables were eventually published, observations proved his predictions to be incorrect. The invention of the quadrant Meanwhile, in , John Hadley had invented the reflecting quadrant, the first instrument capable of making the angular measurements on board ship with sufficient accuracy for the lunar-distance method to work.
Although it was a key development, Hadley was not eligible to claim a reward from the Board of Longitude under the terms of the act. It was a few years later in that the Board gave its first award. The role of the mathematicians and the development of the sextant Spurred on by various prizes offered by the Academy of St Petersburg in the early s, mathematicians and astronomers on the continent published new lunar theories and tables.
In the end, it was Tobias Mayer, who was the first to produce a set of tables of sufficient accuracy for lunar-distances to be derived. Longitude, as a geographical coordinate, identifies east-west position on Earth, with lines of longitude, or meridians, running from pole to pole. There is no naturally occurring zero point, or prime meridian, and so it is for historical and contingent reasons that we have come to measure longitude from a meridian that runs through Greenwich, near London in the United Kingdom.
Longitude was far more difficult than latitude north-south position to measure by astronomical observation. Latitude is defined in relation to the equator and could be calculated by observing the maximum altitudes of the Sun or other stars using instruments such as astrolabes, cross-staffs and back-staffs. Longitude, in contrast, came to be defined in the early modern period as a difficult technical problem that was either insoluble or a challenge to be met with improved mathematics, astronomy and instrumentation.
The problem of finding longitude was, historically, linked to maritime navigation, where a lack of visible reference points in the skies or on land made position-finding particularly difficult. While mariners had means of keeping track of their position, including by dead reckoning where duration and direction of travel at an estimated speed is used to calculate a new position from and old one , it was impossible to calculate longitude directly.
For routes that were largely known especially coastal routes , or that could be navigated by sailing to a particular latitude and then heading directly east or west known as latitude sailing , the inability to fix longitudinal positions accurately could be overcome.
However, as trade routes and imperial ambitions expanded, monarchs, merchants and investors were increasingly interested in the possibility of improved methods of navigation that might increase the scope for expansion and reliability of profits. Western imperialism and commercial expansion underpin the history of longitude, for methods of navigation developed earlier or in other parts of the world did not rely on longitude and latitude coordinates. Between the sixteenth and eighteenth centuries, the interest of states and other patrons in identifying successful longitude methods led to the foundation of institutions — such as observatories, standing committees and schools — and the establishment of monetary rewards.
While theoretical solutions were known, the many scientific and technical difficulties involved in implementing them meant that many considered it impossible. The large sums involved excited public interest and raised the stakes far beyond most contemporary astronomical or calculational problems.
Longitude projectors, seeking investment in schemes, tools and techniques, seen as cheats, fools or, at least, likely to drive themselves and others mad with wasted time and money. The implementation and routinization of successful methods eventually lessened public interest but, in the twentieth century, longitude regained wide recognition as a tale of singular heroic inventors, competitive rivalry, and national triumph.
Curators of relevant collections of scientific instruments have been responsible for much of this research, often reflecting the technical, institutional and national contexts within which they worked.
Longitude remains a classic example where public fascination with science as a story of triumph—individual and national—persists, despite the sustained efforts of scholars to emphasize the importance of context, as well as of social and cultural approaches to history. In ancient Greece, scholars understood difference in longitude as difference in time.
In the second century BCE, Claudius Ptolemy outlined existing methods for establishing geographical positions, particularly those of Hipparchus c. It was known that this phenomenon would appear at the same moment anywhere it was visible on Earth but at different local times. Comparing notes after the event would allow a calculation of the time difference, and so the difference in longitude, between the two locations. This was correct in theory but difficult to put into practice. Comparing the local time of eclipse observations remained the only astronomical method of establishing differences in longitude until the sixteenth century.
However, by the late fifteenth century, Christopher Columbus benefitted from having a copy of the printed astronomical ephemerides published by Regiomontanus, which predicted the positions of the Sun, Moon and planets as they would appear at Nuremburg.
This gave him a reference time against which to compare observations that he made in the Caribbean in and , although errors in both predictions and the observations meant that the accuracy was very poor. Such methods were, however, used to map lands of the Spanish empire in the s—80s and there are examples of English navigators observing eclipses to establish longitudes in explorations of coasts of the Americas in the seventeenth century.
Eclipse observations were more often made to improve geographical knowledge for future navigators than to aid ongoing navigation, and were made once the ship had reached land. While there are examples of Spanish and Portuguese navigators making use of astronomy to establish longitudes in the sixteenth century, dead reckoning remained the core method of navigation.
The errors known to exist in navigational tables and the difficulty of making observations at sea meant that few considered astronomical methods of finding longitude an improvement to existing methods.
However, at the start of the sixteenth century, the possible ways of determining longitudes by astronomy increased. Most significant was the development of the lunar-distance method, described in print by Johann Werner of Nuremburg in and in a roughly contemporary manuscript by Rui Faleiro that was evaluated during the — circumnavigation of Ferdinand Magellan. Nevertheless, small numbers of mathematically adept individuals attached to voyages continued to experiment with and record lunar distances, eclipses, transits and occultations throughout the sixteenth and seventeenth centuries.
Figure 3: A depiction of the lunar-distance method using a cross staff from the work of Peter Apian, courtesy Wellcome Library. While dead reckoning continued to be key, and astronomical methods chiefly circulated in mathematical literature, a third approach was theorized and explored at sea: magnetic variation, or declination. This involved the measurement of the angular difference between magnetic north, indicated by a compass needle, and true north, established astronomically.
This was known to vary geographically, and so held out hope of offering a mappable network against which east-west positions could be fixed. However, the patterns of variation are complex and were ultimately shown to change over time, meaning that any such map would not only require a very large number of observations but would also have to be regularly updated.
As the terms of the act were read with increasing flexibility, it became more a grant-giving mechanism than a competition. Over the years, lots of people were in contact with the Commissioners of Longitude.
Many received money in recognition of their efforts, or to encourage them to improve, test or share their work. The desire of trading organisations such as the East India Company to turn profits from tricky maritime routes, and of the Royal Navy to protect and extend such interests, was crucial.
So, too, was the availability of ships and people to test and develop new ideas. Neither Harrison nor timekeepers solved the problem alone. Not only did Harrison, naturally, make use of the work of predecessors and contemporaries, but it took several others to develop a marine timekeeper that could be put into widespread use. The Commissioners of Longitude were also right to see the timekeeping and lunar-distance methods as complementary.
The latter could be rolled out more cheaply and quickly than the former — and it could be used intermittently to check the performance of a chronometer, preventing error accumulating over the course of a voyage.
In the longer term, the answer was to have multiple chronometers, tested and corrected against the stars at land-based observatories. The aforementioned Whiston and fellow mathematician Humphrey Ditton proposed a signal-based solution using the flash and bang of rockets, set off from known locations, as a positioning system.
The idea worked in theory, but with one big snag: how could rocket platforms be moored in deep waters? The commissioners quickly concluded that this approach was impracticable, because the patterns were neither well mapped nor static. Even into the 19th century, magnetic schemes and instruments were submitted for consideration — but were quickly dismissed. It certainly attracted plenty of cynicism. Surely, it was thought, anyone talking about longitude was misguided, mad or bad, on an impossible quest that would land projector or backer in the madhouse or poorhouse.
The fact that British individuals and institutions were central to solving the longitude problem did not give the nation a significant advantage in the following century — tables, sextants and chronometers were readily traded overseas.
Longitude is related to latitude , the measurement of distance north or south of the Equator. Lines of latitude are called parallel s. Maps are often marked with parallels and meridians, creating a grid.
The point in the grid where parallels and meridians intersect is called a coordinate. Coordinates can be used to locate any point on Earth. Knowing the exact coordinates of a site degrees, minutes, and seconds of longitude and latitude is valuable for military , engineering , and rescue operation s. Coordinates can give military leaders the location of weapons or enemy troops. Coordinates help engineers plan the best spot for a building, bridge, well, or other structure.
Coordinates help airplane pilots land planes or drop aid packages in specific locations. Into the Great Wide Open It was not until the 18th century that people were able to correctly determine their longitude, even though they had been able to figure out latitude for some time. Not being able to reckon longitude was dangerous for sailors.
Without an exact location, they could easily run out of food or water on a long expedition into uncharted territory. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
The Rights Holder for media is the person or group credited. Jeannie Evers, Emdash Editing. Caryl-Sue, National Geographic Society. For information on user permissions, please read our Terms of Service.
0コメント