Global Positioning System Reference
In-Depth Information
the brink of the European Age of Exploration, India already had strong
naval and merchant fleets plying well-established trade routes to China and
Southeast Asia. Following the Arab expansion from the Arabian Peninsula
after the birth of Islam, sea travel became an important factor in the Arabs'
trade and communication. The new Arab lands contained few large navig-
able rivers apart from the Tigris and Euphrates, so ocean-going boats were
developed, along with the mapping and navigational skills to permit voyag-
ing across the Mediterranean, along the Red Sea, down the east coast of
Africa, or across the Arabian Sea (fig. 5.6). By the ninth or tenth century CE
Arab sailors possessed a form of compass—almost certainly acquired from
further east, as we will soon see—and they navigated with the aid of a
kamal
. This instrument was functionally similar to the cross-sta√, though it
took a di√erent form. By measuring the altitude of stars it yielded informa-
tion about latitude and, in combination with the compass and detailed
regional maps, allowed Arab traders to travel the open oceans of their part
of the world. Throughout the Golden Age of Islam (roughly the seventh to
the thirteenth centuries) the Arabs contributed much to navigation by
integrating geographical and technical knowledge from a wide area, from
sources that were previously independent of one another.
The compass originated somewhere in the East, although the date and
place are uncertain. The Chinese first applied naturally occurring magnetic
material to navigation, probably in the eleventh century CE, but the knowl-
edge of such materials appears to be much older. Magnetite is a mineral of
iron oxide that was called
lodestone
. Initially, lodestones seem to have been
used in China for
feng shui
. Subsequently, they were used to magnetize
small needles of iron or steel which, when free to turn, orient along the
earth's magnetic field lines. Navigators found that when magnetized nee-
dles were floated on water (in a wisp of straw or on a small piece of wood) so
that they were free to turn, they could orient north-south.
Wherever and whenever the application of magnetic material first oc-
curred (there are claims that compasses existed in fifth-century India), the
use spread westward. By about 1300 CE the Europeans had learned of
compasses and had improved them. The dry compass—a magnetized nee-
dle free to turn on a pivot (fig. 5.7)—is a European invention, made some-
time before 1410 CE.
16
The mariner's form of this compass was steadily
improved until it became a widely used, though not fully trusted, instru-
16. The idea of placing a magnetized needle on a pivot may have been Chinese, but the
idea of placing the instrument on a gimbal was certainly European.