Arago's meridian
Paris has no shortage of monuments
and statues. The largest monument is the size of the inner city of
Paris itself and extends from the north side of the périferique to
the south side. Yet it is a monument that you can walk past, or right
over it if you don't know what to look out for. The monument to Arago
is the Paris meridian. The monument consists of copper plates of about
5 centimeters that are attached to the sidewalk where the meridian
crosses the streets.
You can follow the whole monument
from the north side of the périferique to the south side (or vice
versa of course). The walk goes (from the north) through Montmartre
over narrow streets, via the 9th arrondisement via the Louvre to the
Seine, over the footbridge over the Seine and then through Saint
Germain du Pres via the Jardin du Luxembourg to the Paris Observatory,
just South of the observatory is the empty plinth where the statue of
Arago once stood. The walk south to the périferique is less
interesting.
And everywhere you are looking for
the medallions on the ground with the name Arago. The medallions are
exactly on the Paris meridian. The Paris meridian is the lesser known
brother of the Greenwich meridian. And both have a whole family of
different meridians. For a long time there was no standard meridian
and it was not necessary. A mapmaker could choose his own meridian and
as long as he used it consistently over his own maps, the maps were
mutually connectable. In the seventeenth century, the map meridian was
preferably placed in the Atlantic Ocean so that there was no east-west
confusion about land. The Greenwich meridian has become the standard
for the map and for standard time measurement. But the Greenwich and
Paris meridians were therefore not competitors. Every city, or at
least every country, had its own meridian to determine the local time
and thus the time for the land (As the Nanjing
meridian was used for the time in China). Until recently, there was
no universal global time standard. Time was determined locally by
measuring the passage of the sun and stars through the local
meridian. So a local meridian was needed for time calculation.
The meridian of Paris was first of
all the basis for the meter and has also been used as a reference for
maps for a long time. The French wanted that piece of history not to
be completely forgotten. When they organized a competition for a new
monument to Arago, a Belgian artist submitted the idea to plot the
meridian through the city. The medallions have been placed on the
sidewalks on the street. It provides a special walk where you walk as
straight as possible through Paris through streets that you would
otherwise not come as a tourist.
Outside Paris the meridian extends
even further and is indicated by a row of trees as la méridienne
verte. In Paris this is not indicated by a row of trees but by a
series with a number of medallions such as the Arago medallions, in
the Jardin de Luxembourg you can see a few. La méridienne runs all
the way from Dunkirk to the Pyrenees, the part that was originally
measured with triangulation to determine the meridian and to determine
the meter.