navigation

navigation, from the latin navis (a ship) and agere (to drive), the art and science of conducting a craft as it moves about its ways. See celestial navigation; coastal navigation; hyperbolic navigation; inertial navigation; satellite navigation. What follows is a short history of navigation.

Navigation Without Artefacts.

When James Cook discovered Oceania in the 18th century the cultures were still at a Neolithic stage of development. But to Captain Cook, perhaps the most illustrious of all scientific navigators, it was a matter of wonder the way the Polynesians navigated ‘from Island to Island for several hundred leagues, the sun serving them for a compass by day and the Moon and Stars by night’. Andia y Varela, leader of a Spanish expedition to Tahiti in 1744, was similarly impressed by the skill of the navigators. ‘When the night is a clear one,’ he wrote, ‘they steer by the stars; and this is the easiest navigation for them because these being many [in number], not only do they note by them the bearings on which the several islands with which they are in touch lie, but also the harbours in them, so that they make straight for the entrance by following the rhumb of the particular star that rises or sets over it.’

The traditional navigation skills of the Pacific islanders will have encompassed the skills of all Neolithic navigators, and of navigators in the China Seas, the Indian Ocean, the Mediterranean, and the seas of northern Europe down to the Vikings of the 10th century and their Norman successors in the 11th. The methods, practised well into the 20th century by indigenous Pacific navigators, have been studied over the years by many scholars. Historically their interest is that they give us an idea of how other cultures in other seas and other centuries navigated before the introduction of the magnetic compass enabled sailing directions and charts to be scientifically based, and navigation from then on founded on measurement. From the navigational point of view no work is more informative than We, the Navigators by David Lewis, which describes his valuable and remarkable fieldwork.

In 1968–9 under a research fellowship of the Australian University Lewis spent nine months in Isbjorn, a 12-metre (39-ft) ketch, investigating native navigation in the western Pacific, learning from the surviving practising navigators and getting them to navigate Isbjorn by their methods. Hippour, as an example, an initiated Micronesian navigator from Puluwat, sailed Isbjorn on a voyage of some 1,840 kilometres (1,150 mls.) entirely without charts or instruments, relying only on his cyclopedic memory of reefs and islands under the stars spanning some 2,400 kilometres (1,500 mls.). Hippour could neither read or write, nor understand the western concept of crossing position lines to fix position.

Basically, indigenous Pacific navigation is a system of dead reckoning based on observation rather than measurement. There are, classically, no artefacts. Waves, winds, clouds, stars, sun, moon, seabirds, fish, the water itself are, to quote another authority, all there is to see, feel, smell, or hear. The navigational task is to integrate information from these sources into a system accurate and reliable enough to guide the mariner to his destination. The process is one of observation, judgement, and experience rather than measurement. The overall objective will be to bring the vessel into what Lewis terms the ‘expanded target area’, where signs of land such as birds, deflected swells, cloud formations, and so on will enable the navigator to home on to his destination.

The methods vary to some extent according to local conditions. In the Carolines, for example, wave direction is used to steer a steady course, whereas in the Marshall Islands, where atolls refract the waves, interference patterns themselves are used for orientation. In the tropics, equatorial stars near the horizon change bearing very little as they rise and set, and the navigator chooses a guiding star for his destination and steers to keep it at a steady angle on the bow. Memory necessarily plays a vital part in the whole process and star courses for a large number of islands (about 60 in the Carolines) will be committed to memory by the navigator under training.

The ocean phase of the voyage may be divided, conceptually, into a number of segments (or etak) corresponding to the apparent passage of a notional reference island under successive navigational stars using a procedure analogous to the running fix. The island is conceived as moving backwards as the canoe progresses and the segments so defined give the navigator his distance travelled and distance run. The first and last segments are identified with the dipping distance of the island of departure and the expanded target area of the destination. The speed at which the reference island is taken to move backwards reflects, of course, simply the accuracy of the dead reckoning. The island is, if you like, a metaphor, a way of organizing navigation information. Like the chart it is an abstraction.

Birth of Navigation Based on Measurement.

In the West at least, navigation based on measurement was born in the Mediterranean and was developed rapidly by the Italian city states during the 13th century. By the end of it, Mediterranean seamen had the magnetic compass (the card already subdivided into 32 points), systematically compiled sailing directions based on compass directions and estimated distances, and the nautical chart drawn from the same information.

It was, above all, the discovery and development of the magnetic compass that made mathematical navigation, the chart, and reliable pilot books possible. It also altered the pattern of Mediterranean trade. Before its introduction the seas were normally closed in winter because of the weather and the difficulty of navigating with overcast skies. Once in use it enabled the number of voyages to be doubled so that the various trading fleets could make two round voyages each year without having to lay up overseas.

The word ‘compass’ originally meant the nautical division of the horizon into 32 ‘points’ rather than an instrument or device of any kind, and compass directions were named after the familiar names of the winds that the seaman distinguished. Pliny, for instance, in his Natural History writes: ‘From Carpathos is fifty miles with Africus to Rhodes’, Africus being a wind; and the pilot bound for Rhodes might well wait for the wind to blow from that quarter before setting sail.

Whether charts were used in antiquity is a matter of dispute, but none seems to have survived. In the late Middle Ages the portulan chart appeared quite suddenly, the earliest surviving example in Italy, complete in all its parts and without apparent parentage. It was mathematically based and the first map of any kind to carry a scale. With the mariner's compass and the sand-glass, which enabled the distance run to be calculated, it provided a self-contained system of navigation that seemed quite adequate for all normal purposes. Indeed, until the 17th century, there was no means of fixing a ship's position offshore in the Mediterranean. However, although voyages might now end anywhere from the Black Sea to Flanders, the Mediterranean seaman would seldom be out of sight of land for long. The fact that he would have followed magnetic, rather than true, courses would have been of little consequence since both the sailing directions and the plain charts (hence the derivation of plain sailing), were based on the same data. Nor did the inadequacy of the plain chart, where the meridians were parallel to each other and did not converge towards the pole, matter much in a sea that stretches east–west over such a narrow belt of latitude. The art of dead reckoning had been perfected, and to all intents and purposes seemed to suffice.

Early Navigation in Northern Europe.

For those navigating the Atlantic coasts of Europe matters were quite different. Here a knowledge of the tides was essential, both to determine the strong tidal streams on coastal passages and to predict the depths of water in ports and harbours. The emphasis in early English sailing directions, for instance, is on soundings and the tides. ‘Upon Portland is fair white sand and 24 fathoms’ runs one passage, showing the northern practice of establishing position on the continental shelf by the depth of water and the nature of the bottom with an early form of lead line.

A later entry reads ‘A south moon maketh high water within Wight, and all the havens be full at west-south-west between Start and the Lizard’, which refers to the practice of telling the time of high water by the bearing of the moon. For it had long been known that although high water does not occur simultaneously at all places on the same longitude it does occur at any one place when the moon is at the same position in the sky. The daily retardation of the tides was well understood. However, for the unlettered seaman, accustomed to telling the time from a compass bearing of the sun—where each of the 32 points of the compass rose represented 45 minutes—one point was, for him, close enough to the true retardation of 48 minutes. The mid-16th-century English pilot's skills in the Narrow Seas, which he shared with the seamen of Normandy and Brittany, were considerable and the waters he navigated were as perilous as any, but they were not the navigational skills required in the ocean.

Early Ocean Navigation.

From the 9th century onwards Norse traders and raiders in their longships and knarrs penetrated into the Mediterranean, and to Iceland, Greenland, and Norway in the north. Little is known of their precise navigational practices beyond what can be gleaned from the sagas, but they reached America some 500 years before Columbus and for centuries conducted regular passages of some 1,400 nautical miles to and from Greenland and Norway without the use of magnetic compass or chart. There is some archaeological evidence that they used a Viking compass, but its use is unlikely to have been critical.

In the 1420s, when the caravels of Henry the Navigator began to sail down the West African coast, a better understanding of the wind and current systems of the Atlantic Ocean became necessary if regular trade routes were to be established. The practice adopted was to take a long board out into the Atlantic, keeping the north-east trade winds abeam until the variables were met with further north and an easterly course could then be laid for home. To achieve this the pilot had to know when he had reached the parallel along which he was to run to his destination. At first this was done by comparing the altitude of Polaris, as observed with the seaman's quadrant, with what its altitude had been at the port of departure (say Lisbon). The difference was of course the difference in latitude but latitude meant nothing to the mariner at that time and was not marked on the charts. The difference in degrees and minutes was thus converted into linear distance by multiplying the readings by 16⅔ (the accepted degree of the meridian) to give the difference in leagues. Later the scale of the quadrant itself would often be marked with the names of ports and landfalls whose latitudes had been established. When the sun replaced the star as the equator was approached, first the mariner's astrolabe and later the cross-staff replaced the seaman's quadrant as the favoured instrument for observation.

Polaris is not, as sailors then believed, fixed in the sky, but circles the pole of the heavens so that its altitude will only correspond to that of the pole twice a day. Astronomers devised a simple rule for using the star to find latitude. Sailors had long used, as a form of clock, the rotation around Polaris of the two so-called Guards (or Pointers) in the Lesser Bear (Ursa Minor), a line from the front Guard (Kochab) to the star representing the hour hand. To help them memorize the midnight position of the Guards at different times of the year they imagined a giant figure in the sky, the pole at his stomach, whose head, feet, and outstretched arms, with cross lines between the limbs, defined an eightfold division of the circle. How this was used for timekeeping need not bother us but the new rules for observing Polaris made use of the familiar imagery to indicate the corrections to the star's altitude for different positions of the Guards. ‘You are to know,’ reads an English manual, ‘that when the Guards are at the head of Polaris, the star is 3 degrees below the axis.’

Developments of Charts and Manuals during the 15th–18th centuries.

When the Portuguese explorers crossed the equator in 1471 Polaris was no longer visible and in 1484 King John II of Portugal appointed a mathematical commission to examine the problem of using the sun to determine latitude at sea, and its conclusions are described in the oldest surviving Portuguese navigation manual, Regimento do astrolabio e do quadrante. This gives seventeen examples of determining latitude from the sun's meridian altitude with different combinations of latitude and declination, as well as rules for ‘raising the pole’ (finding how far the ship must run on a particular course to raise its latitude one degree).

In 1537 the great Portuguese mathematician Pedro Nuñes (1492–1577) published an important study on the errors of the plain chart. Navigation in the Atlantic had now become astronomical and the pilot required a meridian on his chart to identify the latitudes he was expected to attain and then ‘run down’. The problem was that since the plain chart ignored the earth's curvature, an east–west compass course would eventually carry the ship off the east–west line of latitude marked on the chart. Mercator's projection in his world map of 1569 solved this problem by introducing proportionally the same error into the spacing of the lines of latitude as there was in the lines of longitude.

While the Portuguese, and later the Spaniards, were transforming the practices of ocean navigation, the English, although they traded as far afield as Iceland and fished the Grand Banks of Newfoundland, were still following earlier navigational methods. For England at that time lacked the Continent's common mathematical culture, which had led to English ships employing Spanish, Portuguese, or French pilots and having their instruments made in Flanders and their charts in Portugal.

The answer lay in scientific education which, during the latter half of the 16th century, English navigators had just started to acquire. The first English navigation manual was a translation of the leading Spanish one of the time and appeared in 1561 as The Art of Navigation by Martin Cortes. William Bourne, an instructor in mathematics described as an innkeeper, produced a popular version of the book, A Regiment for the Sea (1574), which was perhaps more suited to seamen. Then in 1599 Edward Wright published Certaine Errors in Navigation, perhaps the most important navigational work of the 16th century. It explained Mercator's projection (which Mercator had not) and included a table of meridional parts which gave the spacing of the minutes of latitude along the meridians so that anyone competent in chartmaking could now draw a ‘true’ chart. Seventy years later, John Seller, an instrument maker, chartmaker, and instructor in navigation, published the first volume of his monumental Practical Navigation, a work that demonstrated how completely the navigational climate had changed under the influence of the talented astronomers, instrument makers, and mathematicians who so improved the practice of navigation and led ultimately to English supremacy at sea.

As navigation became increasingly based on mathematics, nautical publications assumed greater importance. For example, amplitude tables enabled the pilot to establish the magnetic variation at any place and so increase the accuracy of his compass readings. In 1686 the great scientist turned navigator Edmond Halley (1656–1742) published his study of ocean wind systems and, in the winter of 1669–1700, undertook a voyage to chart the world's isogonic lines, lines connecting points of equal magnetic variation. The British nautical almanac for 1767 became the first to publish data for the determination of longitude by lunar distance. This method prevailed well after the Board of Longitude had made its award to John Harrison (1693–1776).

Modern Navigational Aids.

Until the 20th century, the only way of establishing a ship's position offshore was still celestial navigation, although improved instruments, from the early quadrants to the modern double-reflection sextant, increased the accuracy and reliability of observation, whilst improvements in nautical tables and almanacs constantly evolved with the growth of nautical astronomy and, latterly, computers. Both the notion of the position line, stumbled across accidentally by the American Captain Sumner in 1837 (it had been missed by the astronomers), and then the idea of the intercept propounded by the French naval officer Marcq Saint-Hilaire, did much to make the principles of celestial navigation more widely understood and to ease the navigator's task.

Electronic aids to navigation, most of which were conceived either during or shortly after the Second World War (1939–45), revolutionized navigation at sea. Radar could obtain the bearing of coastal echoes in poor visibility; electronic echo sounders monitored the depth of water below a ship's keel; the electronic log accurately recorded the distance it covered; and the various hyperbolic navigation systems gave quick, simple, and accurate positions throughout much of the world, day or night. However, it is satellite navigation, with its worldwide coverage, precision, and flexibility, that is the principal aid to navigation today.

Bibliography

Marcus, G. , The Conquest of the North Atlantic (1980).
Ronan, C. , The Shorter Science & Civilisation in China, 3 (abridgment of Joseph Needham's text) (1986).
Seaver, K. , ‘Olaus Magnus and the “Compass” on Hvitsark’, Journal of Navigation, 54 (May 2001), 235.
Taylor, E. , The Haven Finding Art: A History of Navigation from Odysseus to Captain Cook (1954).
Williams, J. , From Sails to Satellites: The Origin and Development of Navigational Science (1992).

Mike Richey