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RT-
6
GREEN
MERIDIAN ROUTE
(Ruta del Meridià Verd)
Dunkerque
- Paris - Barcelona
Introduction
In 1998, the 200th anniversary of the creation of the metre was commemorated.
The length chosen for it was the length of a section of an arch of a terrestrian
meridian, specifically the meridian 002º20'14'', then called meridian
0 (or of Paris), that begins in Dunkerque and ends in Barcelona (although
the real end is in the village of El Masnou).
It is obvious
that, in order to take this decision, the French parliament estimated
different possibilities and several ways to determine this new measure
("metre" from the Greek word "metron").
But the idea
of creating what lately was called "Decimal Metrical system"
was much older. It was by the end of the previous century, in 1670, when
the vicar of the parish of Sant Pau of Lyon, Gabriel Montou, ideated a
universal measure, unique and based in nature. He proposed a decimal system
based in the length of an arch of a meridian, that is an angle of a minute.
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When looking
for antecedents of this decision, there must be taken into account
the Benedictine monk Gerbert
d'Orlhac, who became the Pope Silvestre II. His contribution,
in the 10th century, was the assumption and broadcasting of the
number zero
in the numerical European system.
It is
obvious that this contribution was not intentionally related with
the determination of the length of the metre, but it helped that
mathematicians had enough knowledge in order to realise those measures.
In the same way, it is also evident that, without this contribution,
the binary system (1-0) could not exist about a thousand years later,
and computers and any other software systems could not exist.
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Gerbert
d'Orlhac (938 [?]-1003) was born in Auvergne, Aquitania, and was a monk
of the monastery of Saint-Géraud d'Orlhac. But he studied mathematics,
astronomy, and other sciences, in Vic, Ripoll and Barcelona, thanks to
the relationship that the Spanish culture had with the Moslem culture,
because they were who really introduced the concept of number zero, as
well as many other things, especially those related with agriculture,
medicine, etc.
Green Meridian Route
In the
year 2000, several French and Catalan civic-minded associations, with
the support of the administrations of both countries, organised several
activities to commemorate the 200th anniversary of the establishment of
the Decimal Metrical System and the measurement of the longitude of the
meridian Dunkerque - Paris - Barcelona.
Altimetrical
plaque in the façade of the CEC.
(Photography by: J.M. Jerez)
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Among
those activities, it is necessary to emphasize the planting of thousands
of trees along this imaginary line in France and several walkings
organised by the Centre Excursionista
de Catalunya lin the most significative points of the geography
of Catalonia that were used as geodesical vertex of the measurement.
They put up several commemorative plaques in several places (Montjuïc
castle, Rellotge tower in the Pescadors harbour, and in the central
office of the CEC in Barcelona, Alella, Tarragona, in the peak of
the Puigsacalm, etc). See the magazine "Muntanya" of the
CEC, number 797 (February 1995). |
In order
to give a future prospection to this event, as well as to a reunion perspective
with nature, several authorities accorded to rename it as Meridià
Verd (Green Meridian). One of the proposals was to arrange and
mark a route as close as possible to the historic meridian of Paris that
was able to be integrated in the net of mountain routes of the country.
The route in Catalonia begins in Coll de Pal, next to the peak of the
Costabona, in the Pyrenean crest, and ends in Masnou, next to the sea.
The beginning and ending places are very specific, but the route has to
follow paths and roads, what makes almost impossible to follow exactly
the straight line by which the meridian goes on, although this was the
main aim when designing the route.
In some specific places,
because of the characteristics of the land, it is not possible to go by
mountain bike. Those users have some alternative routes called special
variants (not marked).
Historical
origins
Nowadays, to measure
lengths we use the metre and its dividings (decimetres, centimetres, and
milimetres). It seem that those measures have existed for ever, but they
are only 200 years old.
By the Desember 10th, 1799 Act, the measure called "metre" was
born but, from where does its length come from? The history of the determination
of this length is as complex as exciting, and an important part of it
happened in Catalonia.
In the past, other measures were used, as the stick, measures that had
different lengths according to the different places. In front of this
confusion, different governments and monarchies tried to unify them.
The scientific advances in the 18th century, especially in the fields
of geography, optics, geometry and astronomy, motivated the serious study
in order to search a universal unit of measurement based in a geographical
dimension, like the terrestrial meridian.
Everything began in 1790. In the framework of the radical changes that
the French revolutionaries wanted to introduce in laws and usages of the
ancién régime, the bishop Carlos Mauricio of Talleyrand
proposed in front of the French National Assembly a really revolutionary
proposal.
In France, there was the constant request of an estate unification and
control of the different measurements used in every city and region of
the country. The several abuses and scandals, more than the diversity
of measurements, made unbearable a chaotic measure system, but only a
revolution could change the ancient feudal order.
Talleyrand,
an skilfull politician, proposed a measure system absolutely new, based
in nature in order to be against nobody, an standard that could be accepted
by any nation (especially England), and perfect to become a universal
measure. The chosen pattern was the length of a pendulum oscillating at
intervals of one second at 45 degrees.
His proposal
was approved by the French National Assembly in May 8th, 1790, and the
king Louis XVI formally invited the king of England to collaborate in
the determination of this new measure.
England did
not answer. France was alone in its trying to create the universal measure
and tried another way. In March 19, 1791, the Science Academy of Paris
proposed the substitution of the pendulum by another measure from nature.
The metre could be the ten-million part of the quadrant of a terrestrial
meridian. In March 26th, the National Assembly approved the change and
the new measure project, that need the help of almost all the members
of the institution.
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The
new unit was called METRE (from the Greek metron, that
means "measure") and was parted in decimal fractions: the
decimetre (the tenth part of the metre), the centimetre (a hundreth
part of the metre) and the milimetre (a thousandth part of the metre).
In front of
the impossibility to measure a quarter part of the meridian, from
the North Pole to the equator, the answer was to measure a part
and to calculate the total value. The arch tried was the one between
Dunkerque, near the North sea, and Barcelona, in the Mediterranean
coast of the Iberian peninsule.
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Why
Barcelona?
The March 19th report
widely explains the convenience of placing the inferior end of the arch
in Barcelona. The most important reasons are scientific: to choose as
the basic meridian the one that passes by the observatory of Paris, repeteadly
measured in France, both ends were at the sea level, and the meridian
of Paris touched the sea in Barcelona. Barcelona, in addition, was far
enough of the Pyrenees in order that its high could not affect the direction
of the vertical. The mid point of the arch was placed near the parallel
45 if the measurement was inside France, what gave several advantages
in the final reckoning.
But, as some
important scientific said, those reasons were mere non-scientifical justifications.
The expected mistakes in such a complicated calculation prevented from
the pretended exactitude. There were other extra-scientific reasons behind.
As several journals said, this operative hided an attempt of the Sciences
Academy to show its validity as the real basic scientific entity in a
country where its dissolution was planned from a long time ago. Another
use of the measure of this arch was that to include Barcelona will give
internationality to the new measure, it would not be only French. Spain,
apart from England, was a really important nation in Europe, and its participation
would be determinant.
The decision
had been taken. March 30th, 1791, a dispossessed of power Louis XVI signed
the project of the Science Academy and encharged the topographers
Pierre
François André Méchain and Jean
Baptiste Joseph Delambre to
measure the meridian.
Delambre measured from Dunkerque to Rodez, and Méchain measured
the rest.
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The used technique
was the geodesical triangulation. They drew several triangles (its vertexs
were some of the mountains placed along the meridian) and calculated their
dimensions by measuring 2 basis (or lengths between 6 and 10 km), by using
the called "Academy toesa", the measure that had to be substituted
by the metre.
They had to
decide which mountains they had to use, climb to those mountains and measure
from there the angles made by the neighbour peaks. Méchain began
by the Spanish side. In April 22nd, 1792, Charles IV, king of Spain, accepted
the French proposal and appointed two civil mathematicians: José
Chaix, vice-director of the observatory of Madrid, and Juan de Peñalver,
together with the sailors José González, the captain of
the brig "Corzo", and Francisco Planes, Miguel Bueno and Miguel
Alvarez.

The
measurement in Catalonia
Méchain arrived
to Barcelona in July 10th, 1792. He and Gonzáled stablished the
work methodology. They chose the necessary mountains between Barcelona
and the Pyrenees that had to be the vertexs of the Catalan triangles and
discussed a new project that the Spanish members proposed to the French
astronomer: if the arch ended in Majorca instead of Barcelona, its mid
point was much more exactly on the parallel 45. To accept this proposal
meant to go down to the South, chose more mountains and draw new triangles,
and to go to Majorca to make an internal triangulation in the Balearic
islands.
This lengthening idea was proposed by the sailor and astronomer José
de Mendoza, who was in Paris and who went with the members of the Academy
who were preparing the new metrical system.
Méchain did not have the authorization for this enlargement when
he arrived to Spain. But he received it by letter of the French National
Convention by October 27th, 1792. Until then, France and Spain had approved
the triangles and began to measure them. Those triangles were in the peaks
of the Calmelles, Mare de Déu del Mont, Puigsacalm, Rocacorba,
Puig Rodó, Matagalls, Montserrat, Mont Mates, Vallvidrera, Santa
Creu de l'Olorde and Montjuïc, the most eastern point of the first
projects, in the outskirts of Barcelona, where Méchain arrived
by October 29th.

Castle of Montjuïc in Barcelona. (Photography by: J. M. Jerez)
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Méchain arrived
to Barcelona in July 10th, 1792. He and Gonzáled stablished the
work methodology. They chose the necessary mountains between Barcelona
and the Pyrenees that had to be the vertexs of the Catalan triangles and
discussed a new project that the Spanish members proposed to the French
astronomer: if the arch ended in Majorca instead of Barcelona, its mid
point was much more exactly on the parallel 45. To accept this proposal
meant to go down to the South, chose more mountains and draw new triangles,
and to go to Majorca to make an internal triangulation in the Balearic
islands.
This lengthening idea was proposed by the sailor and astronomer José
de Mendoza, who was in Paris and who went with the members of the Academy
who were preparing the new metrical system.
Méchain did not have the authorization for this enlargement when
he arrived to Spain. But he received it by letter of the French National
Convention by October 27th, 1792. Until then, France and Spain had approved
the triangles and began to measure them. Those triangles were in the peaks
of the Calmelles, Mare de Déu del Mont, Puigsacalm, Rocacorba,
Puig Rodó, Matagalls, Montserrat, Mont Mates, Vallvidrera, Santa
Creu de l'Olorde and Montjuïc, the most eastern point of the first
projects, in the outskirts of Barcelona, where Méchain arrived
by October 29th.
Méchain
began measuring the azimuth of one of the last triangles' side, and the
latitude of one point, in the moat of the castle of Montjuïc, the
eastern side of the arch. After those first measurements, he came back
with González, who was the virtual operations director in the Spanish
side, and with the rest of the scientifics to the northern stations in
order to finish the measure of the angles between the vertexs of the established
triangles.
Once all expeditionaries had come back, in Desember 1792, González
went to Majorca in his ship in order to decide which mountains had to
been used and to put light in them (a combination of mirrors and fire),
in order than Méchain could check if the measure was possible.
From the top of the Puig Major of Majorca, in Desember 16th, González
lighted a fire towards Montjuïc, a light that Méchain could
see with his telescope but not with the glasses to measure angles. Méchain
decided that, with his instruments, it was not possible the geodesical
union of the Balearic islands and the Catalan coast, in the north of Barcelona.
The astronomer finished all the operations of determining the latitude
of Montjuïc, and he prepared himself to go back to France.
But an unexpected event altered his plans. In January 21st, 1793, Louis
XVI was guillotined in Paris, and the war was going to start between France
and Spain. The General Captain of Catalonia allowed him to continue his
studies in Catalonia but he could not go near the border, in order than
his activities at the tops of the mountains could not be interpreted as
espionage.
Méchain could do nothing, so he diverted himself by doing several
astronomical observations, like the lunar eclipse of February 25th, 1793,
and by visiting several Catalan intellectuals. He sent one of his most
trustful collaborators, Tranchot (a geographical engineer) to the southern
mountains in order to look for a better place to unite with the Balearic
islands. It was during one of this visits to a doctor's house (maybe Francesc
Santpons i Roca), in order to wacth how a machine worked, that Méchain
suffered a serious accident that obliged him to rest in bed for five months.
The war against
France, declared in March 7th, went on; but Méchain got permission
to finish the border stations, but not to go back to France. Meanwhile,
Tranchot, risking his life, crossed the border in order to prepare the
French stations to connect all the triangulations.
In November 3rd, 1793, the last measurements in Catalonia finshed. In
this year, the provisional pattern was built, using incomplete data. Two
years later, in 1795, France took oficially the measure system based in
the metre.
Once back to Barcelona,
and in front of the impossibility to go back to his country nor having
access to the castle of Montjuïc (a militar area in war time), Méchain
entertain himself calculating the latitude of his balcony in the Fontana
d'Or, placed in the Escudellers street. By means of a small chain of geodesical
triangles, he tried to connect his balcony with his first observation
point in Montjuïc and try to check the lately determined latitude.
The discrepancy between both measures, about 3 seconds of arch, was not
notified by Méchain to the comission, and his decision was severely
criticized.
By the end of 1794,
the appointment of a new General Captain, much more favorable, allowed
Méchain to leave Catalonia towards Italy, from where he came back
to France. The astronomer stopped in Marseille, where he stayed for about
half a year because of several excuses. From there, and before going back
to Paris, deeply affected by revolution and terror, Méchain went
to the French side of the Pyrenees in order to finish the chain of triangles.
He spent almost three years in his measurements from the tops of the Puig
de Calmelles and the Puy de l'Estella, last Spanish stations and the first
French one, until Rodez. Finally, even Delambre had to travel to the south
in order to measure a comprovation base in Perpignan. Finally,
Méchain and Delambre met in Carcassone and, together, they came
back to Paris by the end of August, 1798, with several data of the measures
made between Barcelona and Dunkerque. In November, the delegations of
the countries that accepted Talleyrand's invitation met for the very first
time in order to help in the needed calculations in order to determine
the new metrical system. Among those delegates, there could be found Gabriel
Ciscar and Agustín de Pedrayes. For six months, those calculums
were made in order to mathematically determine the exact measure, as well
as measures for capacity and weight (litre and kilogramme). Finally, in
June 22nd, 1799, the representant of Holland, Van Swinden, read in front
of the rest of the delegates the final conclusions. After long sessions
and some not very justified decisions, they decided that a metre will
measure 3 feet, 11 lines and 296 thousandths of line, almost 0.32 milimetres
less than the one calculated in 1795. A French "toesa" will
measure 1, 9490366 metres.
An Act passed by Frimario
19th of the year 8 of the French Republic (Desember 10th, 1799), signed
by the French first consul, Napoleon Bonaparte established it with the
following lema "For all the people, for any time". The
definitive measure for the metre, and the new Metrical Decimal System
were born.

Verification
of the accuracy of the metre
In Van Swinden's report,
there cannot be seen than the Catalan operations have finished. According
to Méchain's plans to enlarge the measure until Cabrera, Van Swinden
said: "... We expect that more favourable circumstances allowed the
execution of what could not be done by now."
Those circumstances came in 1802. In the minutes of the Bureau des Longitudes,
the French organization in charge of astronomy and geodesics, in August
31st, 1802, there can be found the news that one of its members, not identified,
wants to continue the geodesical operations in Spain. Méchain,
who was capitain concierge (or responsible of the observatory of Paris)
by that time, was invited to give his opinion. In a report addressed to
the Home Secretary, there was the proposal of arriving to Ibiza, going
down by the Catalan mountains until Tortosa in order to find the points
from where it was possible to find this island. This proposal was justified
by the intention of being as much exact as possible. By the same time,
and although the reticences of other astronomers (who wanted a younger
man), Méchain asked to lead this expedition.
In October 13th, 1802, Méchain received the order to travel to
Barcelona and to the Balearic islands. He asked for the permission and
collaboration of the king of Spain. Once this permission was achieved,
Méchain prepared himself to travel to Barcelona. In May 1803, after
a pleasant trip, he arrived to Barcelona with three companions and was
ready to compliment the General Captain of Catalonia, the Count of Santa
Clara.
Observatory of
Paris, 18th century
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If his first trip
was full of favourable conditions, in this one everything was delays.
The General Captain did not received orders from Madrid; the promised
ship (under the orders of Enrile) was in Cartagena, and the good weather
for shipping was going by. Méchain, desperate, wrote to his ambassador
in Madrid to ask him if he could facilitate all the procedures. In August
17th, 1803, Méchain could observe from Tortosa a solar eclipse.
He climbed all the highest southern mountains in order if he could see
the Balearic islands.
He did not have enough means to go to the Balearic islands, so he began
a series of measurements of triangles during September and October 1803.
From the area of the Montsià, in south side of the river Ebro,
he went to Llaberia (north of Tortosa), Sant Joan (near Altafulla), the
Puig de la Morella (in the massif of the Garraf) and, finally, at the
top of Montserrat, an old station that allowed the connection of measurements
with the ones made in the last expedition.
Meanwhile, Enrile's ship, who was near Barcelona, was turn aside to Menorca
in a quarantine of the yellow fever. Méchain tried to get a new
ship, but he could not. Chaix, tired, came back to Madrid, and the French
astronomer accepted the help of a friar Mathematics professor from Barcelona,
called Agustí Canelles, as well as the help of a noble man from
Valencia, astronomer amateur, called Faust Vallés i Vega, 12th
Baron of the Pobla Tornesa and la Serra d'en Galceran.
Méchain
could do anything, so he decided to go to Valencia in order to know if,
from its mountains, it was much easier to see the Balearic islands. With
the Baron, they both climbed to one of the Baron's properties, the massif
of the Desert de les Palmes, in the north side of Castellón, from
where Ibiza can be seen. Méchain rested in the Baron's houses until
he got another ship. Méchain came back to Barcelona, and in January
8th, 1804, he shipped to Ibiza, where he arrived in January 15th.
When he climbed
to the Ibizan mountains, he confirmed the high dificulty to see the Catalan
coast. He had two options: on one hand, to link the Balearic islands through
Majorca in a big triangle based in Montsià, Desert de les Palmes
and Puig Major and, from there, draw an internal triangle in the islands;
on the other hand, to go by Ibiza, down the coast of Valencia until Cullera
and Dénia. When he climbed to the Puig Major, he finally decided
to proceed according to the first option.
But, answering
his requests, the Bureau des Longitudes ordered him to proceed
according to the second option.
Méchain,
exhausted, did not dare to contradict his partners of Paris, so he ship
to Valencia, where he arrived by the end of April 1804. He rested in the
Baron's house, measure several latitudes, and searched for the perfect
place in the Albufera to measure the base of the triangle. Later on, he
climbed to several other mountains trying to find the perfect place.
Once those stations
were decided, Méchain came back to Cullera in order to begin with
the measurements, but he discovered that from the highest place near the
village, it was really difficult to see Ibizan mountains. He began to
measure the coast crest, where he contracted the malaria because of the
mosquitos. In Espadan he fell ill, and he was descended to Castellón,
in the Baron's house, where Méchain died in the Baron's arms in
September 20th, 1804.
Méchain,
one of the most glorious French astronomer, is buried in the cemetery
of Castellón. A scientific trip, transformed in an impressive and
unlucky adventure, finished in this moment. His helpers went back to France
with most of the instruments and notes, leaving others if a reprisal was
possible.

Continuation
of Méchain's works
If, in 1802, it was quite interesting to check the metre's exactitude,
in 1806 this problem was irrelevant. The problems of the metre were more
of implementation than of exactitude. The scientific world had assimilated
that the Earth was not a perfect ellipse, that not all meridians are not
the same and that the legal metre was just the distance between two lines.
The scientific problem of those days was to measure correctly the arches
of the Earth. In this environment, Laplace, the most influent scientific
of France, directly asked to the Emperor Napoleon the continuation of
the measurements of Méchain in Catalonia in order to enlarge the
meridian of Paris
This proposal
was accepted, and the Emperor appointed Jean
Baptiste Biot, an important scientific, and
Jean François Dominique Aragó, from Estagel,
a young secretary of the observatory of Paris, who could speak Catalan,
in order to continue Méchain's works. In September 20th, 1806,
two years after Méchain's death, they arrived to Barcelona, together
with a Spanish Mathematician who was in Paris called José Rodríguez
González. They interviewed with the count of Santa Clara, they
received the necessary permissions and continued travelling to Tarragona
and Valencia.
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Mola de s'Esclop (926 m) serra de Tramuntana (Mallorca)
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Ruins of a hut
used by François Aragó at the top of the Mola de s'Esclop
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In Valencia, they
met José Chaix, reassigned to this operation, who, for about two
years, covered the southern Catalan mountains, as well as in Valencia
and in the Balearic islands, in another really interesting scientific
and human adventure that will be explained by Aragó, by the end
of his life, in this book "History of my Youth". They wanted
to enlarge the meridian of Paris from Barcelona to the island of Formentera
and to check that there was only 2 milimetres of difference with the previous
measure.
During the 19th
century, several countries implemented the new Metrical System, but few
of them adopted it in the real life. In Spain, the Metrical System was
legally implemented by the April 15th, 1848 Act, and was compulsory from
January 1860. But, although all those acts, almost everybody used the
same measure units as before.
For the second
half of the 19th century, both systems lived together and, slowly, mainly
because of education and of the unifying advantages of the new system,
it was definitively used in almost all fields.
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Barcelona, Montjuïc,
the Catalan, Valencian and Balearic mountains, and most of its most characteristic
places belong to the metre's history. For most of the Catalan people,
the only memory are the names of two streets: Meridian avenue and the
Parallel.

Information
about some of the Catalan collaborators of the French scientifics who
measure the meridian.
Canelles
i Carreres, Agustí
Ciscar i Ciscar, Gabriel
Chaix Isniel, Josep
de Martí i Franquès,
Antoni
Salvà
Campillo, Francesc
Santponç i
Roca, Francesc
Vallés i Vega,
Faust
Commemorative
acts of the measure of the meridian of Paris
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By
the foot of the geodesical vertex placed at the top of the Puigsacalm,
there is a commemorative plaque of the 200 anniversary of the measure. |
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In Ocata beach,
in El Masnou, in September 23rd, 2003, commemorative sign that places
the meridian of Paris in this point.
Also in September 23rd there was the presentation of the Green Meridian
route's guide there.
Photos: J.M. Jerez
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| In
the Torre del Rellotge, in the Pescadors harbour of La Barceloneta
(Barcelona) there is a commemorative plaque from 1999 of the 200 anniversary
of the measure. (Photography by: J. M. Jerez). |
Castle of Montjuïc (Barcelona)
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| There
is a commemorative plaque of the 200 anniversary of the measure in
the tower that was the base for the flag. (Photography by: J. M. Jerez).
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The work of Valérie Berjeron "La talla
mètrica de la natura" ("The metrical woodwork of
nature"), that links the lineal metre to its natural time.
In the north-eastern side of the moat of the castle, with a wonderful
view over the sea, around a concrete tower of 9 metres high, there
are three different kinds of trees: an ilex (Quercus suber), an apricot-tree
(Prunus armeniaca) and a white poplar (Populus alba bolleana). (Photography
by: J. M. Jerez).
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| In
the centre of the Plaça de les Glòries Catalanes there
is a memorial to the meridian, a work of the French sculptors François
Scali and Alain Domingo, that represent the most significative lengths
and highs of the meridian of Paris. (Photography by: J. M. Jerez). |
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In
the village of Vallfogona de Ripollès, there is a parade with
a monolith dedicated to the Green Meridian. (Photography by: J. M.
Jerez). |
Marks
of the route of the Green Meridian
Explicative soffit of the meridian placed in the south of the Serra
Cavallera.
(Photography by: Jordi Embodas)
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Vertical mark of the route.
(Photography by: J.M. Jerez)
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Horizontal mark
of the route. (Photography by: J.M. Jerez).
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Marks in stickers in urban places.
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Links
related with the meridian of Paris
The metre in Catalonia
http://www.uv.es/~ten/metro.htm
The metre in Barcelona
http://www.astrogea.org/ipa/galeria/bcnmetro/index.html
The Green Meridian
in France
http://www.icilacreuse.com/carte/meridien/
http://www.ville-rungis.fr/corps_merid.htm#paris
http://www.apgi.net/andouque/nouveaut.htm
http://www.ac-clermont.fr/actualit/pedago/2000france/piquenique.htm
http://www.chez.com/t3m/doc-douzet-meridien-zero.htm
http://saint.martin95.free.fr/lameridienneverte.html
http://smdsi.quartier-rural.org/meridiv/meridiv.html
http://perso.wanadoo.fr/arverne.03/huriel/meridienne.html
http://www.espace-ecoles.com/animation/info/la_meridienne_verte.htm
http://www.aude.pref.gouv.fr/actualite/act-br-meridienne.htm
http://www.obs-nice.fr/bijaoui/Arago/sld082.htm
http://gallica.bnf.fr/anthologie/notices/00414.htm
A metre of history
http://www.el-mundo.es/larevista/num184/textos/metro1.html
Department of Metrology
http://www.metrologia.csic.es/defmetro.HTML
Records of the
metre
http://www.culturaclasica.com/cultura/sistema_metrico.htm
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