Global Positioning System Reference
In-Depth Information
Al-Biruni
The eleventh-century polymath genius Al-Biruni, unknown in the West until
modern times, was a true scientist in the modern sense: he made careful
observations and measurements and drew conclusions based on these, inde-
pendently of any prevailing mythology. An Uzbek who lived much of his life in
(and died in) Afghanistan, then part of the Persian world, Al-Biruni wrote in
Persian and Arabic and spoke several other languages, including Hebrew and
perhaps Greek.
Al-Biruni wrote treatises on the astrolabe and other navigational instru-
ments and made a study of map projections. He estimated the distance be-
tween the earth and the sun, believed that the earth was a sphere that rotated
about its axis, and considered it just as likely that the earth orbited the sun as
the other way around. Half a millennium before triangulation became well-
known in Europe, he employed it to estimate the earth's radius to within
17 km of the true mean value (such accuracy was not achieved in the West
until the sixteenth century). He also measured the rate at which the earth's
rotation was slowing down.
Al-Biruni's scientific interests extended beyond geodesy to astronomy,
mathematics, mineralogy, and optics. Outside of science, he was keenly inter-
ested in Islamic law, India, linguistics, and astrology, the last of which he
refuted repeatedly.
Europe since classical antiquity. I will have much more to say about the
instruments of surveying and about triangulation in a later chapter. Here, I
introduce triangulation as a finished product, a tool that came to be used
throughout the seventeenth century to make increasingly accurate geo-
detic measurements. Indeed, Snell himself used triangulation to survey the
distance between two Dutch towns in 1615 and from his data was able to
estimate the earth's radius to within a few percent.
In 1669 a French priest, Jean-Felix Picard, used triangulation to form an
accurate map of the area around Paris. This was the beginning of a monu-
mental survey that would map the whole of France—the first survey to
cover an entire country. Picard also wanted to measure the length of a
meridian arc (a line stretching north-south that covers at least a degree of
longitude) and so estimate the size of the earth, using Snell's methods but
improving on his result. Picard chose as his southern point Malvoisine, an
estate which lay some 30 km south of Paris (today, an obelisk in Malvoisine
