Geoscience Reference
In-Depth Information
MAKING a map is a matter not only of determining the orientation of the map and
the latitude and longitude of places on it but also of knowing the scale. This was
done by surveying techniques, determining the distance between places on the
meridian by physical measurements with standard measuring sticks and chains, and
by triangulating with theodolites, or their historic equivalents. These techniques,
called
geodesy
5
,
were used to lay out the Paris Meridian and to relate it to places in
the rest of the country and the rest of the world. The accuracy and the scope of the
work were unprecedented. The result was to produce an accurate map of France for
the use of sailors navigating along the coast and for administrative purposes, and
these maps were the first maps of an entire country that were grounded in accurate
scientific measurement.
In 1693 the need for the new maps was demonstrated by an outline map of the
coastline of France after the first measurements had been made by the new tech-
niques, compared in 1693 with the most accurate earlier map. Brest in Brittany had
been moved to the east of its previously assumed position by more than a whole
degree of longitude (about 140 km), and the older map had overestimated the area
of France by a fifth (
Fig 5
).
The demonstration of the technique was timely and was extended to map not just
France but its possessions overseas. In 1682 René Robert Cavelier (Sieur de La Salle)
had just claimed the American territory of Louisiana for the French king (for whom
the territory was named). He had the vaguest idea of the position and extent of this
territory exemplified by his death in 1687. Setting out through the Gulf of Mexico for
the mouth of the Mississippi River, he landed instead in what is now Texas, 1000 km
away. His men lost confidence in their commander. They murdered him.
As we shall see, the techniques were extended even beyond the boundaries of
individual countries. They were used to determine the size and the shape of the
whole world, and even prove the scientific law that holds the whole Universe
together. What an edifice to build on the abstraction of the Paris Meridian!
5
You would think that
geometry
(from
geo-
earth and
-metria
measuring) would be the relevant
word, and in early times it might have been, more so than now.
Geometry
was associated with the
practical art of measuring and planning and was used especially in connection with architecture.
But by the seventeenth century it had come to mean the properties of spaces, including lines and
surfaces, and had taken on its present mathematical meaning.
Geodesy
(from
geo-
earth and
-daiein
divide) came into English to mean the measuring of land, and in the nineteenth century it
developed its modern meaning of the branch of applied mathematics that relates to the figure of
large areas of land and Earth as a whole.
