PUSULA, HARİTA VE ROTA:
SEYİR BİLİMİ VE SANATINDA İSLAMİ ETKİLER

Norman J.W.Thrower

Bu çalışmanın amacı, seyirle ilgili yeryüzünün keşfini kolaylaştırmış olan önemli bazı gelişmeleri ve aktarımları tartışmak ve örneklemektir. Osmanlı Amirali, haritacısı ve coğrafyacısı Piri Reis (ölümü 1559) ilk gelişmelerden yararlanmış ve katkıda bulunmuştur. Bu gelişmeler arasında manyetik pusula, portolan haritaları, rüzgar ve akıntı bilgileri bulunmaktadır. İlerleyen gelişmelerle bu araçlar keşif döneminde (1500-1800) önemli rol oynamışlardır. Bu periyot süresince dünya kıyıları keşfedilmiş ve zamanın denizci ulusları tarafından haritalanmıştır.

COMPASS, CHART, AND COURSE :
ISLAMIC INFLUENCES ON THE ART AND SCIENCE OF NAVIGATION
Norman J.W.Thrower

ABSTRACT

The aim of this paper is to discuss and illustrate selected examples of navigational developments and transmissions, which facilitated the exploration of the Earth. The Ottoman Admiral, cartographer and geographer Piri Reis (died 1559) was the beneficiary of earlier developments and contributed to these. They included the magnetic compass, the portolan chart and knowledge of winds and currents. With further development they proved crucial in the age of reconnaissance (1500-1800). During this period the coasts of the world were discovered and charted by the navigators of maritime nations.

BİLDİRİ

Let me begin by saying that I am grateful to Rear Admiral Nazim Cubukcu, and other organizers of the International Piri Reis Symposium, for the kind invitation to participate in this conference.  Secondly I wish to thank Gregory C. McIntosh for giving me the opportunity of writing the foreword to his book, The Piri Reis Map of 1513, published in the year 2000 CE.  This required me to look more closely than I had previously at the life and work of the great Ottoman admiral, navigator, and cartographer, Piri Reis.

I am not an authority on Piri Reis, as many here are, but I will attempt to put his work in a global context.  My qualifications for this include teaching the history of cartography for over forty years at the University of California, Los Angeles (UCLA).  In addition I was employed in the Survey of India between 1942 and 1946, and lived for much of that time in what is now Pakistan.  At that period the Survey of India employed many Muslim scholars and technicians, whom I came to admire. My talk on “Compass, Chart, and Course”, will deal with these three elements up to, including, and beyond the time of Piri Reis.  I will leave to others, better qualified than I am, to discuss Piri Reis and his contributions.

The origin of the magnetic compass, an instrument fundamental to the making and understanding of Piri Reis’s map of 1513 and other maps, is obscure.  Nearly one hundred and fifty years after the death of Piri Reis, the English astronomer Edmond Halley wrote a poem, in Latin, dedicated “to the unknown inventor of the nautical compass.”  But it was not so much an invention, as a development.  As in so many developments the earliest mention of the magnetized needle appears to be in the literature of China.  Of course, magnetic attraction had been observed in many places long before it was recorded.  The distinguished Sinologists Joseph Needham and Wang Ling in their monumental study, Science and Civilization in China, give a reference to the south-pointing magnetic needle, at least by the 8th Century CE. 

Figure 1

By this time Islamic peoples were well established on the coast of China and became aware of this, and many other Oriental developments.  The early Chinese were of the opinion that the magnetic needle pointed to a highly magnetized area to the south of their large country.  Needham and Ling assert that the transmission of the magnetic needle, if not the magnetic compass itself, from East to West, “cannot be questioned,” to use their expression.  If so, the transmission of this very important instrument was by Muslim navigators, because the Chinese were not yet sailing as far to the West as they were to do later, under Cheng Ho, and others.  The vessel that enabled Islamic sailors to navigate so far from their homeland was the dhow, fitted with lateen, or triangular, sails.  Figure 1 is a photograph taken recently of an Islamic dhow in the Indian Ocean with two triangular, or lateen, sails, oars, and with a smooth, sewn-plank hull, a very efficient vessel.  The Europeans thought that the lateen sail, which enables a ship to sail ‘close to the wind’, came from the Latin world hence the term, but actually it came from the Middle East.  We will deal with this very important Islamic development later in this essay with respect to Spanish, Portuguese and other voyages in the Atlantic.  The contemporary Chinese on their junks, and the early Greeks and Romans, and later, the Norse, apparently used only the square sail, not the triangular sail.

Figure 2

Another important Middle-Eastern development was the improvement of the astrolabe, or star measurer.  Figure 2 is an image of the oldest, extant astrolabe, made by Ahmed ben Khalaf in the ninth century CE.  Apparently the Islamic astronomers and artisans improved on an instrument that had been previously invented in Alexandria, Egypt, in Classical times. No example from that period, and location, survives.  Basically the astrolabe is a stereographic projection of the celestial sphere showing all great circles and their intersecting angles, correctly.  By manipulating the several moving parts of the astrolabe, the navigator can accurately observe star positions and measure their altitude and azimuth.  The astronomer’s astrolabe is an elaborate and costly instrument and would have been used only on land at this time, and not by navigators at sea. 

Figure 3

The sailor’s version (Figure 3) is simpler and smaller, about 5 to 8 inches (1/5th of a meter) in diameter, but heavier.  It was employed to find the altitude of the Sun at noon, from the moving deck of a ship, to give an indication of latitude.  This instrument was used in conjunction with nautical tables of solar declination, from day to day.  Toward the end of the 16th Century, (after Piri Reis’s time), positions of the more prominent ‘fixed’ stars were added to the tables.  The mariner’s or sailor’s astrolabe was much more useful in the Indian Ocean, than it was in the latitudinally narrower Mediterranean Sea.  Eventually the astrolabe was superseded for use at sea by instruments, which were only parts of a circle: the quadrant, the sextant and the octant.

An instrument that was of greater use in navigating the Mediterranean before, during, and after Piri Reis’s time, was the magnetic compass.  During the late European Middle Ages, and the Early Renaissance there was a close (and fortuitous) correspondence between magnetic and astronomical (or geographical) North, in the Mediterranean.  Before the earliest portolan charts that we know about were made, Islamic cartographers were producing the best terrestrial maps, and also the best celestial globes, in the West.  In this period Muslim astronomers had greatly reduced the length of the Mediterranean Sea, from Ptolemy’s 62 degrees longitude in late Antiquity, to a correct figure of 42 degrees by Al Zarquali in the 12th century CE.  This correction probably came from land-based observations, and was not widely disseminated information.  Thus, it was to be over four centuries after this time before cartographers in Western Europe were to represent the length of the Mediterranean correctly on their maps.  For example, on his maps, Gerhard Mercator, in the mid 16th century CE, used a measure too long by 10 degrees longitude, for the Mediterranean Sea.  Figure 4 is an illustration of the oldest surviving celestial globe, an Islamic bronze construction, dated from internal evidence at 1279 CE.

Figure 4

The most important cartographer in the pre-portolan chartmaking period in the West, and comparable to the best contemporary mapmakers in China, is Al Idrisi.  Abu Abd-Allah Muhammad al Sharif al Idrisi, to give him his full name, lived from 1100 to 1160 CE.  Idrisi was indebted to earlier Islamic travellers for much of the information on his maps, but he also travelled widely himself, to gather data. He journeyed from his native Morocco to Asia Minor, and was invited by the Norman King Roger II to his court in Sicily. 

There Idrisi made a world map with curved parallels that is superior to any contemporary European map of this genre (Figure 5).  Like all of Idrisi’s maps it has South orientation. By comparison, Figure 6 illustrates a contemporary European, so-called T-O map, showing a tri-continental, presumably flat Earth; the three continents are divided by narrow seas, and the map is oriented to the East. In addition to his circular map, Idrisi also made an atlas with detailed maps, as this example of part of the coast of Greece, with offshore islands, shows (Figure 7). However, Idrisi’s most ambitious work is a large rectangular map in seventy sheets known as the Tabular Rogeriana, named for his patron, King Roger. Figure 8 is the whole map, reconstructed.   

Figure 9 is a detail with part of North Africa at the top and Iberia in the center, with offshore islands, and Figure 10 is the same illustration with familiar North orientation for easier recognition.  Idrisi’s maps continued to be important, especially in the Islamic world, for centuries after his death.

But soon a new kind of chart appeared, based on the magnetized needle, a device which had been in use for centuries before it was satisfactorily mounted to make the magnetic compass. According to tradition this was first accomplished in Amalfi, Italy, at the end of the 13th century CE.  The compass consists of a box containing a pivoted magnetic needle mounted over a card, on which 16, and later 32 directions, were marked.  Figure 11 illustrates the component parts, and the fully assembled magnetic compass.  The directions on the card were named for winds, following the practise in Antiquity, hence the name, wind (or compass) rose, indicating principal directions.  This idea came from Classical Greece, as evidenced by the Tower of the Winds, surviving to this day in Athens.  At first verbal descriptions of directions only, called portolani, were available to the navigator. But with the help of the magnetic compass, a new cartographic form was developed by the late 13th century CE, the portolan chart (Figure 12).  It is inferred, because the genre is fully developed by the time of this chart, the earliest surviving example, the Carte Pisane, ca 1290 CE, that earlier ones may be lost.  Naturally, there must have been a great attrition rate as these charts were used at sea.

Figure 13

Figure 13 is an engraving of the Carte Pisane, which, as its name suggests, was presumably made in Pisa, Italy.  Such charts were produced in other Italian coastal cities also, including Genoa, and in the Balearic Islands, off the coast of Spain.  This technology soon spread, so that at least by CE 1461 (or 865 in the Islamic calendar), one Ibrahim Al Mursi, who was from southern Spain, constructed a portolan chart.  Probably Islamic chart makers were constructing portolan charts well before this time because there was, in the pre-Conquista period, in Spain, a great sharing of technology between Islamic, Christian, and Jewish scholars and artisans.  Certainly, the portolan chart tradition was well accepted in the Islamic world before the time of the birth of Piri Reis (ca. 1470 CE). The rhumb lines can be faintly seen, radiating from equally spaced wind roses on this illustration; the map also features place names, perpendicular to the coasts.

The manner in which these charts were used is as follows: to obtain a compass bearing, the navigator would draw a straight line from the place where he was, to the place to which he wished to sail. He would then plot the correct bearing from the closest rhumb line, transferring this with the help of a parallel ruler.  Then, with a magnetic compass, the navigator would attempt to sail as closely as possible in that direction. Because the portolans were working charts and heavily used, very few have survived.

Portolan charts delineated the shape of Mediterranean and Black Sea coasts with remarkable accuracy. Figure 14 shows the coast of the south of Italy and Sicily from the Carte Pisane in a firm, continuous, or solid line.  Plotted against this, with a dotted line, is the same coast from a modern navigational chart.  It is said that the delineation of the coasts of the Black Sea was not improved over the portolan charts until the 19th Century.  This was not so true of areas beyond the Mediterranean and Black Sea coasts, as the portolans were extended to include areas in the Atlantic Ocean, the North Sea, and elsewhere.  Figure 15 is believed to be a self-portrait of the portolan chart-maker Pietro Vesconti on the corner of a chart from his atlas dated 1318. For intersecting rhumb lines on the chart itself, black is commonly used for principal ones, and red or green for intermediate ones. Later the portolan charts became more elaborate, as illustrated by one by Petrus Rosselli of 1456, with flags to indicate sovereignty; these and, the toponyms, have often been researched (Figure 16).

 But new areas were being opened up for chartmakers by overseas discoveries of sailors attracted to Sagres, SW Portugal (Figure 17) by Prince Henry, the Navigator -- the objective was India.  At first the Portuguese dominated this activity, including chartmaking; but they employed artisans from the Mediterranean and Northern Europe, as needed. Figure 18 is a map by Henricus Martellus Germanus, 1489, which celebrates the rounding of the Cape of Southern Africa by Bartholomeu Dias, the previous year (1488), after over 60 years of effort by the Portuguese.  A decade later Vasco da Gama reached the coast of southern India by sailing across the Indian Ocean from Malindi, East Africa.  It is highly unlikely that the Portuguese at that time would have reached India by sea, had they not engaged an Islamic pilot, Ahmed ibn-Majid, to navigate the fleet eastward, toward the end of a long voyage.  Utilizing the monsoonal winds, and having mastered open ocean navigation, Islamic sailors were well acquainted with this route long before the arrival of the Europeans.

Later Piri Reis was assigned to the Indian Ocean fleet and commanded ships on the Red and Arabian Seas. Figure 19 illustrates an assemblage of European ships in the mid – 16th Century.  It delineates, among others, an oared galley and also a caravel with lateen sails – the ship the Portuguese initially preferred.  Most prominently, the illustration features, in the center, a carrack with both square and lateen sails.  It was in such ships, and later, the similar galleons, that the overseas discoveries were made in the New World. The square sails were used when there was a following wind, but these would be hauled down, and only the lateen sails used to get these lumbering ships through the Doldrums.  Five years before da Gama reached India by sea, Columbus thought that he had reached India by sailing westward from Europe in 1492 for Spain. Figure 20 shows the tracks of his four Atlantic voyages. The discoveries of the Portuguese and the Spanish are very important in the cartography of Piri Reis – he used information from both of these sources, along with others, as discussed by several authors in this publication.

To complete this overview I would like to indicate, very briefly, what happened after the death of Piri Reis. The northern Europeans now enter the picture: the French, the English, the Dutch, the Danish, and others.  Theoreticians from various countries postulated ideas, to be proved or disproved by the navigators.  One of these was that the magnetic compass was not pointing to the Pole Star, as previously thought, but that the earth itself is a great magnet; with geographical poles being coincident, with the magnetic poles.  This could result in a simple relationship between longitude and the Earth’s magnetic field, an idea overthrown by Edmond Halley and others, in the 17th and 18th Centuries (Figure 21).  Figure 22 is a detail of Halley’s Atlantic chart of isogones, as they are called, which indicates a magnetic pole far distant from the geographical North Pole. Moreover, the position of the magnetic pole migrates very slowly through time, changing the magnetic field and requiring revision of isogonic maps. 

In this paper summarizing early navigation and cartography, we have seen contributions, through the centuries, from a number of civilizations, including, very importantly, the Islamic World.