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.
Nevertheless, in particular locations, at certain periods of time, it could be an effective means of locating a ship. In the s, drawing on observations of variation, Vicente Rodrigues identified locations in which magnetic north aligned with true north. Although the hypothesized positioning of magnetic poles and global patterns were erroneous, both Portuguese and Dutch mariners could make limited use of magnetic variation as a means of finding their position.
As imperial competition and trade rivalries developed in the sixteenth century, there was increasing investment in solutions to the problem of longitude. Mathematical practitioners and projectors of schemes for new or improved methods often succeeded in persuading those with money and power that financial support would pay off with workable methods. In the late seventeenth century, convinced by members of their academies that improved knowledge of positional astronomy would render the lunar-distance method viable, the kings of both France and England established observatories, in Paris in and at Greenwich in Charles II also founded a Mathematical School in , designed to train future naval officers in the methods that would support astronomical navigation.
Money put into finding ways to fix positions against the invisible lines of longitude often resulted in visible and long-lasting scientific institutions.
From this, you could work out how far apart the two places were in terms of longitude. The problem was that no timepiece existed that could be set at home and relied on to keep time accurately while at sea, where pendulums were notoriously unreliable.
So, even if local time could be determined from the noonday sun, there was no time to compare it against. This was the problem that Harrison set out to solve. Despite this, Harrison was initially awarded only half the promised amount. On a voyage from England to Jamaica in —62, H4 lost just five seconds in over two months at sea.
It was now possible for a navigator to determine local time by measuring high noon, and compare this to the absolute time, which had been set on an accurate chronometer at the start of the voyage. At long last, both latitude and longitude could now be determined accurately, and for the first time you could say exactly where on Earth you were.
Today, it's all done electronically through GPS, a world-wide radio navigation system made up of a constellation of 24 satellites and their ground stations. These 'artificial stars' are used as reference points to calculate a terrestrial position to within an accuracy of a few metres.
In fact, with advanced forms of GPS you can make measurements to within a centimetre! What would Harrison have made of it? Fisher D. Larijani L. As a tribute to the historian Lisa Jardine, who died on October 25th, we're republishing her essay on the shady history of 17th Century timekeeping. How do you measure latitude or longitude?
Here's a step-by-step guide on how to work out your latitude and longitude. This free course, Geography in education: exploring a definition, is aimed at geography teachers, or those with an interest in studying or teaching geography. It looks at the contribution that geography can make in the education of young people and the characteristics and purpose of geography as a subject.
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Latitude has long been comparatively easy to establish by measuring the height of objects in the sky from the horizon. For example the further you are from the equator, lower the Sun will be appear on the horizon. In the Northern Hemisphere, European sailors by the 17th and 18th centuries used cross-staffs to measure the angle of the North Star.
Their calculations were perfected with tables accounting for eye height and the bending of light through the atmosphere. Time, speed and distance have a direct, mathematical relationship and knowing two of the three values allows you to calculate the third. However, until the advent of a clock which was reliable at sea, it was extremely difficult to know the time back at Port A when you were on Ship B. Clocks of the 17th and 18th centuries were unreliable at sea.
In fact, few clocks of the time were reliable in the way we assume clocks to be today. 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. Mayer was encouraged by Euler to apply for a reward from the Board of Longitude. In , he sent a copy of the tables to Admiral Lord Anson, First Lord of the Admiralty and President of the Board, along with a model of a portable instrument of his own design.
Campbell incorporated these along with the best elements of the Quadrant into a new instrument, the marine sextant that he went on to develop with the instrument maker John Bird. His methods were later explained by Lalande in the edition of the French Almanac Connaissance des Temps published for the year It contained diagrams for graphical solutions and tables of pre-computed lunar-distances every four hours for the month of July.
He also took with him a copy of the Connaissance des Temps. The method though remained impractical for all but a handful of people due to the complexity of the calculations required, Maskelyne himself having taken up to four hours to complete them. Now called H4, it was first tested on board ship in Shortly before he died in , Mayer had prepared a more accurate set of tables, which his widow subsequently sent on to the Board of Longitude who arranged for them to be tested by Maskelyne on the same Barbados trip.
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