The Third Dimension

Among the institute’s 25 elegant compasses made of wood and brass, with magnetized iron needles, perhaps the most historically significant is the simple copper ring with Arabic lettering designed by Ahmad ibn Majid, the great Arab navigator. According to Sezgin, Ibn Majid was the first to mount a magnetized needle on a revolving support above the compass face. Earlier, the professor had eagerly hauled out a copy of one of Ibn Majid’s maps, probably similar to one employed on Vasco da Gama’s 1498 voyage from East

Africa to India, and marveled over its accuracy: It pegged the distance between Africa and Sumatra to within 40 minutes of a single degree of longitude, off by the equivalent of around 74 kilometers (46 mi).

“Eighty percent of the history of cartography until the 18th century dates from the medieval Islamic period,” Sezgin asserts. “Only 20 percent came from the ancient Greeks and from later European sources.” As proof, he lays before me copies of Chinese and Korean maps that use Arab, not European, place names, and a 1669 French map by Nicholas Sanson that also recycles Arabic longitudes and latitudes. Sanson’s map repeats a mistake al-Ma’mun had made about the location of Balkh, in northern Afghanistan, 800 years earlier. Since Muslim cartographers had corrected the error by the 16th century, it is clear that Sanson, working more than a hundred years later, was copying al-Ma’mun’s original map, Sezgin says.

Wandering through the museum provides an eye-opening course in eight centuries of Muslim science and Europe’s liberal appropriation of Islamic discoveries. In one room are 10 instruments that the 16th-century Danish astronomer Tycho Brahe modeled on instruments from the 13th-century Maragha observatory in northwestern Persia. Among the dozens of gleaming brass astrolabes and equatories—related instruments used to determine celestial longitudes—is one designed on an Arab model by Geoffrey Chaucer, the 14th-century English author of The Canterbury Tales, to instruct his son in astronomy.