Global Positioning System Reference
In-Depth Information
FIGURE 2.6.
Ab u Rayh an Muhammad ibn Ahmad Bır unı (Al-Biruni).
Adapted from an old
Iranian painting.
sidered so far because it required only one observer at one location, as you
can see from figure 2.5b. He measured the dip angle to the horizon from
the top of a mountain. Knowing the height of the mountain, he calculated
the earth's radius.
The light of science in general, and of geodesy in particular, may have
gone out in Europe, but it burned brightly in the Islamic world. Much of
the earlier learning of the Greeks was known to Islamic scholars (both Al-
Mamun and Al-Biruni read Aristotle, for example) and would return to
European knowledge through them.
10
Battle of the Bulge
The modern era of geodesy began early in the seventeenth century with a
Dutch astronomer and mathematician, Willebrord Snell.
11
Snell took ad-
vantage of recent developments in instruments and mathematics to de-
velop the system of measuring distances via
triangulation
. The telescope,
the theodolite and its ancestors, and the invention of logarithms combined
to permit distances over land to be measured with an accuracy unknown in
10. For Al-Mamun and Al-Biruni, see Buttimer and Wallin (1999);
Encyclopedia Britan-
nica
, s.v. ''Biruni''; Glick, Livesey, and Wallis (2005, pp. 88-90); Harley and Woodward
(1987, p. 141); and Lindberg (1978, chap. 1).
11. Snell is known to physicists in the English-speaking world for his law of optics.
