Article 313: Columbus Owes Arabs His Maps to Discover The New World-America. Part II
Hasan A. Yahya, Ph.Ds, a writer from the Holy Land
From several of his other biographers, most notably the Spanish priest Fray Bartolome de las Casas, it is also known that Columbus was an avid reader of books on geography and cosmography. Four of the books he owned have been preserved: a 1485 Latin translation of the "Book of Ser Marco Polo", an Italian translation of Pliny's "Natural History" printed in 1489, Pierre d'Ailly's "Imago Mundi" and minor treatises, and a 1477 edition of the "Historia Rerum Ubique Gestarum" by Pope Pius II.
Columbus also admitted relying heavily on information he gleaned from the school of navigation founded by Prince Henry of Portugal, often known as Henry the Navigator. Around 30 years before Columbus's first voyage, some of the prince's caravels had sailed west, to the outer edge of the Azores and perhaps as far as present-day Newfoundland. Concluding that there were other lands to explore beyond what Ptolemy had described in his second-century "Guide to Geography", and eager to retain and organize the geographical information in the possession of sailors and navigators--many of them from the Levant--the prince established the school at Sagres, in southern Portugal, to act as a sort of clearing house for present and future knowledge of the sea. It may have been from this source that Columbus discovered that when, years earlier, Vasco da Gama had sailed along Africa's east coast, he was guided by an Arab pilot, Ahmad ibn Majid, who used an Arab map then unknown to European sailors.
And yet, despite all this available information, Columbus made a major miscalculation of the distance he had to sail to reach the other side of the globe.
That the earth was a sphere was not a new idea, and it was widely accepted by well-educated people in Columbus's time. So was the Greeks' division of the spherical earth into 360 degrees, but where sources differed was on the question of the length of a degree. The correct measurement, we know today, is about 111kilometers (60 nautical miles) per degree at the equator. In the third century BC, the Libyan-born Greek astronomer Eratosthenes, director of the library at Alexandria, had come up with a remarkably accurate calculation of 100 kilometers (59.5 nautical miles) per degree; in the second century, the great Alexandrian geographer Ptolemy had calculated the degree at 93 kilometers (50 nautical miles). In the ninth century, Muslim astronomer Abu al'Abbas Ahmad al-Farghani, whose works were translated into Latin during the Middle Ages and who--under the name Alfraganus—was studied widely in Europe, had calculated that a degree measured 122 kilometers (about 66 nautical miles)--not as accurate a result as that of Eratosthenes, but better than Ptolemy's.
Either Columbus erroneously used Roman miles in converting al-Farghani's calculations into modern units of distance--thus coming up with a figure of 45 miles per degree at the equator--or, after first deciding that al-Farghani's figure was right, chose in the end, perhaps for reasons of policy, to follow the revered and irrefutable Ptolemy, whose "Geography", in its first printed Latin edition, had gained great popularity in 15th-century Europe. In the first case, Columbus would have underestimated the distance he had to sail to reach Asia by a third; in the second, by some 25 percent.
Had Columbus but accepted the ninth-century findings of a consortium of 70 Muslim scholars, working under the aegis of Caliph 'Abd Allah al-Ma'mun, who had gathered them to determine the length of a degree of latitude, he might have avoided many mistakes.
Using wooden rods as measures, the caliph's scholars traveled a north-south road until they saw a change of one degree in the elevation of the pole star. Their measurements resulted in an amazingly accurate figure for the earth's circumference: 41,526 kilometers, or 22,422 nautical miles--the equivalent of 115.35 kilometers per degree. By Columbus's time, a wealth of knowledge gleaned from Arab science and exploration rested in the libraries of Spain and Portugal. Al-Biruni had accurately determined latitude and longitude and--six hundred years before Galileo—had suggested that the earth rotated on its own axis. One hundred years later, in the ninth century, the mathematician al-Khwarizmi had measured the length of a terrestrial degree and Arab navigators were using magnetic needles to plot accurate courses. It was around this time, too, that the Arab astronomers Ibn Yunus and al-
Battani--or Albategnius, as he was known in Europe--improved the ancient astrolabe, the quadrant, the sextant and the compass to the point that, for hundreds of years afterward, no long-distance traveler could venture forth without them. By the 12th century, the Hispano-Arab geographer al-Idrisi had completed his voluminous world atlas containing dozens of maps and charts (3)
In calculating the distances he had to travel to reach India and the Orient, Columbus chose not to rely on the Arab and Muslim sources. He was, instead, greatly persuaded by the theory of Paolo Toscanelli, a Florentine physician who dabbled in astronomy and mathematics. When he saw Toscanelli's charts stating that Marco Polo's estimate of the length of Asia was correct, and that it was only 3000 miles from Lisbon westward to Japan and 5000 to Hangzhou, China, Columbus accepted the figures he wished most to hear. It was Toscanelli's chart he took with him on his first voyage of discovery. Columbus also believed that his voyage west from Spain to India, though difficult, would be short. Using maps and information based on the calculations of Ptolemy and Martin Behaim, the German cartographer, he believed he could reach China after no more than a 4000-mile voyage. This notion was confirmed by Pierre d'Ailly's "Imago Mundi", a book that, according to Columbus's son and biographer Ferdinand, was his father's bedside companion for years. (Columbus's copy, its margins covered with hundreds of hand-written notes, is in the Seville museum.) D'Ailly believed that the western ocean, between Morocco and the eastern coast of Asia, was "of no great width." He followed the system of Marinus of Tyre, a second-century Greek who made Eurasia very wide east to west, and the Atlantic Ocean narrow, and predicted that the latter could be crossed in a few days with a fair wind.
According to Columbus's log--the original of which has been lost, or, as some historians suggest, destroyed--he sailed his tiny fleet of three small ships to the New World by dead reckoning. his means he crossed the vast expanse of Atlantic Ocean between the Canary Islands and the Bahamas using only a mariner's compass and dividers, a quadrant and lead line, an ampolleta, or half-hour glass, a ruler, and charts. His charts were sheepskins that showed the coasts of Spain, Portugal and North Africa, the Azores, Madeira and the Canaries. He took his course from his mariner's compass, developed from the magnetic needle used four centuries before by Arab navigators. His quadrant was an early invention of the great Arab astronomer Ibn Yunus of Cairo.
There is no doubt that Columbus deserves to be celebrated, in this anniversary year, for his courage, perseverance, sailing skills and superb navigational ability. On the other hand, one can only wonder what might have happened that October day 1492 had he heeded eight centuries of Arab invention and navigational knowledge. Certainly it would have made his navigation easier, his fears fewer, and his landfall more accurate. (1270 words) www.askdryahya.com
______________________________________
Notes:
3. See "Aramco World", July-August 1977.
Source:
Aileen Vincent-Barwood, in "Aramco World" (January/February 1992, Vol. 43, No. 1, pp. 5-9)
http://www.millersville.edu/~columbus/data/geo/VINBAR01.GEO
From several of his other biographers, most notably the Spanish priest Fray Bartolome de las Casas, it is also known that Columbus was an avid reader of books on geography and cosmography. Four of the books he owned have been preserved: a 1485 Latin translation of the "Book of Ser Marco Polo", an Italian translation of Pliny's "Natural History" printed in 1489, Pierre d'Ailly's "Imago Mundi" and minor treatises, and a 1477 edition of the "Historia Rerum Ubique Gestarum" by Pope Pius II.
Columbus also admitted relying heavily on information he gleaned from the school of navigation founded by Prince Henry of Portugal, often known as Henry the Navigator. Around 30 years before Columbus's first voyage, some of the prince's caravels had sailed west, to the outer edge of the Azores and perhaps as far as present-day Newfoundland. Concluding that there were other lands to explore beyond what Ptolemy had described in his second-century "Guide to Geography", and eager to retain and organize the geographical information in the possession of sailors and navigators--many of them from the Levant--the prince established the school at Sagres, in southern Portugal, to act as a sort of clearing house for present and future knowledge of the sea. It may have been from this source that Columbus discovered that when, years earlier, Vasco da Gama had sailed along Africa's east coast, he was guided by an Arab pilot, Ahmad ibn Majid, who used an Arab map then unknown to European sailors.
And yet, despite all this available information, Columbus made a major miscalculation of the distance he had to sail to reach the other side of the globe.
That the earth was a sphere was not a new idea, and it was widely accepted by well-educated people in Columbus's time. So was the Greeks' division of the spherical earth into 360 degrees, but where sources differed was on the question of the length of a degree. The correct measurement, we know today, is about 111kilometers (60 nautical miles) per degree at the equator. In the third century BC, the Libyan-born Greek astronomer Eratosthenes, director of the library at Alexandria, had come up with a remarkably accurate calculation of 100 kilometers (59.5 nautical miles) per degree; in the second century, the great Alexandrian geographer Ptolemy had calculated the degree at 93 kilometers (50 nautical miles). In the ninth century, Muslim astronomer Abu al'Abbas Ahmad al-Farghani, whose works were translated into Latin during the Middle Ages and who--under the name Alfraganus—was studied widely in Europe, had calculated that a degree measured 122 kilometers (about 66 nautical miles)--not as accurate a result as that of Eratosthenes, but better than Ptolemy's.
Either Columbus erroneously used Roman miles in converting al-Farghani's calculations into modern units of distance--thus coming up with a figure of 45 miles per degree at the equator--or, after first deciding that al-Farghani's figure was right, chose in the end, perhaps for reasons of policy, to follow the revered and irrefutable Ptolemy, whose "Geography", in its first printed Latin edition, had gained great popularity in 15th-century Europe. In the first case, Columbus would have underestimated the distance he had to sail to reach Asia by a third; in the second, by some 25 percent.
Had Columbus but accepted the ninth-century findings of a consortium of 70 Muslim scholars, working under the aegis of Caliph 'Abd Allah al-Ma'mun, who had gathered them to determine the length of a degree of latitude, he might have avoided many mistakes.
Using wooden rods as measures, the caliph's scholars traveled a north-south road until they saw a change of one degree in the elevation of the pole star. Their measurements resulted in an amazingly accurate figure for the earth's circumference: 41,526 kilometers, or 22,422 nautical miles--the equivalent of 115.35 kilometers per degree. By Columbus's time, a wealth of knowledge gleaned from Arab science and exploration rested in the libraries of Spain and Portugal. Al-Biruni had accurately determined latitude and longitude and--six hundred years before Galileo—had suggested that the earth rotated on its own axis. One hundred years later, in the ninth century, the mathematician al-Khwarizmi had measured the length of a terrestrial degree and Arab navigators were using magnetic needles to plot accurate courses. It was around this time, too, that the Arab astronomers Ibn Yunus and al-
Battani--or Albategnius, as he was known in Europe--improved the ancient astrolabe, the quadrant, the sextant and the compass to the point that, for hundreds of years afterward, no long-distance traveler could venture forth without them. By the 12th century, the Hispano-Arab geographer al-Idrisi had completed his voluminous world atlas containing dozens of maps and charts (3)
In calculating the distances he had to travel to reach India and the Orient, Columbus chose not to rely on the Arab and Muslim sources. He was, instead, greatly persuaded by the theory of Paolo Toscanelli, a Florentine physician who dabbled in astronomy and mathematics. When he saw Toscanelli's charts stating that Marco Polo's estimate of the length of Asia was correct, and that it was only 3000 miles from Lisbon westward to Japan and 5000 to Hangzhou, China, Columbus accepted the figures he wished most to hear. It was Toscanelli's chart he took with him on his first voyage of discovery. Columbus also believed that his voyage west from Spain to India, though difficult, would be short. Using maps and information based on the calculations of Ptolemy and Martin Behaim, the German cartographer, he believed he could reach China after no more than a 4000-mile voyage. This notion was confirmed by Pierre d'Ailly's "Imago Mundi", a book that, according to Columbus's son and biographer Ferdinand, was his father's bedside companion for years. (Columbus's copy, its margins covered with hundreds of hand-written notes, is in the Seville museum.) D'Ailly believed that the western ocean, between Morocco and the eastern coast of Asia, was "of no great width." He followed the system of Marinus of Tyre, a second-century Greek who made Eurasia very wide east to west, and the Atlantic Ocean narrow, and predicted that the latter could be crossed in a few days with a fair wind.
According to Columbus's log--the original of which has been lost, or, as some historians suggest, destroyed--he sailed his tiny fleet of three small ships to the New World by dead reckoning. his means he crossed the vast expanse of Atlantic Ocean between the Canary Islands and the Bahamas using only a mariner's compass and dividers, a quadrant and lead line, an ampolleta, or half-hour glass, a ruler, and charts. His charts were sheepskins that showed the coasts of Spain, Portugal and North Africa, the Azores, Madeira and the Canaries. He took his course from his mariner's compass, developed from the magnetic needle used four centuries before by Arab navigators. His quadrant was an early invention of the great Arab astronomer Ibn Yunus of Cairo.
There is no doubt that Columbus deserves to be celebrated, in this anniversary year, for his courage, perseverance, sailing skills and superb navigational ability. On the other hand, one can only wonder what might have happened that October day 1492 had he heeded eight centuries of Arab invention and navigational knowledge. Certainly it would have made his navigation easier, his fears fewer, and his landfall more accurate. (1270 words) www.askdryahya.com
______________________________________
Notes:
3. See "Aramco World", July-August 1977.
Source:
Aileen Vincent-Barwood, in "Aramco World" (January/February 1992, Vol. 43, No. 1, pp. 5-9)
http://www.millersville.edu/~columbus/data/geo/VINBAR01.GEO