Looking Around for Arago's Markers

photo: observatoire de paris

No iron, no wood; the Paris Observatory is locked
up tight behind iron today.

Walking the Meridian In Paris

Paris:- Saturday, 6. March 1999:- It is not often that I get to play in Paris on a Saturday, but school holidays in this past week make it a necessity today. The sky says very changeable - with variously colored clouds scooting over swiftly from the west.

The unfamiliar Porte d'Orléans has been picked as the spot for the rendez-vous with Allan Pangborn, and it turns out he has found the fall-back because the number one 'treffpunkt' on the corner of the place does turn out to be an office of La Poste instead of a café.

Allan is on the trail of the 'Arago' markers; the line of 135 little bronze disks set out along the Méridien de Paris - which is the world'sphoto: mire sud old zero longitude, but is now 2º20'14"* east of the new zero at Greenwich, set in 1884. France and Ireland didn't adopt the new 'zero' until 1911.

He has already found the 'mire nord' - or north bearing - up on Montmartre - just to the east of the Moulin de la Galette - and we are looking for the 'mire sud.'

With our noses to the ground looking for the small disks, we overlook the tall 'mire sud.'

As the sky threatens us with rain, sleet and bright winter sunlight in two-minutes intervals, we stroll east on the Boulevard Jourdan to the Cité Universitaire and the Parc Montsouris opposite it.

Inside the park, the France-Météo building is a very low affair, and we think it will be close to the line. There is one odd tower and one other medium-high monument, which we fail to notice. Allan thinks the 'Arago' markers are off the actual line and we have to hunt around quite a bit before we find we are nearly standing on one.

This first disk, like all the others, is about 10 to 15 centimetres in diametre, embedded in a paved path in the park. The soft, old bronzephoto: arago disk color does not make it stand out. Besides the name 'Arago' in raised engraving on it, there is also an 'N' and a 'S.'

Here is one of the pesky Arago things; close to my nose - too close to the camera.

This is a clue to finding the 'mire sud' and of course it turns out to be the sizeable monument we walked past without noticing. This may make us sound like some particularly blind detectives, but practically nothing in Paris is on any straight north-south, east-west axis, and there are few really straight streets. On a day with poor sun orientation, it is all the harder to figure out a compass direction.

The 'mire sud' is a stone pole about six metres high. It has 'mire sud' engraved in its stone with the date of 1806. It also has another inscription, which begins 'In the reign of...' and the rest has been removed, just like that particular person.

There is also a little marker on its east side, with the height: 76 M 754. This is 'mouse mountain' after all, and not the dizzy heights of Montmartre.

This is a good start: one 'Arago' disk and the 'mire sud.' We look at Allan's map, to see if we can follow the markers to the Observatory. It looks like there might be some SNCF rails in the way, so we have to guess how to skirt these and stay on the 'line.'

Going north through the Parc Montsouris we find a number of other markers. Even in a place with fairly open sight-lines, it is not easy. The last one within the park turns up about where Allan thinks it will be. I am hopeless at this sort of thing.

But out on the Avenue René Coty it is not so clear. Allan takes the middle divider strip and I take the east sidewalk. At intersections, we search both east and west streets a bit to see if any disks are hiding on the 'line,' but we don't find any.

The Rue de la Tombe Issoire sort of lines up with the 'mire sud' and the Paris Observatory so we go up it. After crossing the Boulevard Saint-Jacques, Allan finds one and then there are about three in the minuscule Place de l'Ile de Sein, which has a monument to Arago. On the other side of the boulevard of the same name, there is the observatory up on a slight rise.

All of its iron gates are padlocked and the signs say 'closed.' As we walk around its block Allan tells me about the telescope he built, from a kit for $18. He lucked into a professional glass grinder, who did the glass and the reflector, but had to stick with a cardboard tube for the barrel. It was 300-power he said, and he used it a lot.

At the observatory's front door off the Rue Cassini, we find its gates locked up tightly too. A sign says to see the gardien at 77. Avenue Denfert-Rochereau, so we walk around to there.

After getting through their gate which is worthy of the Santé prison we've just nearly passed on the Boulevard Arago, the watchmen turn out to be a jolly crew of two, willing to try out their English. It's impossible to stop them in fact.

About the Méridien de Paris they have nothing, know nothing. Their tip is to hit the observatory's library on Monday - it is open to the public all the time from 10:00 to 18:00 except on weekends.

There are tours to the observatory open to the public, but since the guides are a selection of the resident astronomers, you have to ask for a Saturdayphoto: arago monument reservation in writing. The address is below.

Although I am having a fine time looking for 'Arago' disks, I have to get other things done. Allan agrees to accompany me to Montparnasse, and on the way we take a short-cut through the Montparnasse Cemetery.

I don't know it well enough to wheel him past some of my favorite dead people, so I am concentrating on the shortest route.

This momument to Arago, stands on the meridian, just south of the Observatory.

By total chance - Allan's sharpshooter eyes! - we happen on the tomb of Le Verrier. It's inscription says something like, 'born someplace or other, 1811; died at the Observatory, 1877.' Died with his eyes glued to a 'scope.

Some time after Arago, Urbain Le Verrier was twice head of the observatory and is credited with 'Le Cercle Méridien' in 1834. He also discovered the planet Neptune for the first time, in 1846.

Here's how it started: Louis XIV asked Colbert to build an observatory. To plans drawn up by Claude Perrault, it was started on 21. June 1667 and completed in 1672. For scientific reasons the building contains no iron, and for fire safety reasons, contains no wood.

Each of its four sides, face directly north, south, east and west - probably the only building in Paris situated like this. Its south face lines up with north latitude 48º50'11"* and this is Paris' official latitude. The meridan cuts through the exact centre of the building on it north-south axis.

Inside there is a spiral staircase with 330 steps, which descends to the bottom at 27 metres underground. This is a place with constant temperature and air pressure. While the observatory used to be the world's time centre, it still sets France's official time; and its clock has been giving vocal time since 1933.

But back in 1669, Louis XIV had Colbert call on Jean-Dominique Cassini in Italy to run the observatory. He did this sophoto: tomb le verrier, montparnasse well, that its management stayed in the Cassini family for a long time; the last died at nearly 100 in 1845. The street in front of the main entrance is named after the Cassinis.

Of the other directors, six have had local streets named after them. They are, in order of birthdates starting in 1701, La Condamine, Méchain, Laplace, Delambre, Arago and Le Verrier.

Le Verrier's tomb in the Montparnasse Cemetery, not far from the Observatory.

Some time ago I mentioned that a tree was planted on the old meridian line at Saint-Martin-du-Terre last 25. November. Similar trees are to be planted along the meridian's 1,200 kilometre length between Dunkirk and Perpignan.

For Tuesday, 14. July 1999, a picnic has been planned to take place - on - the meridian; from one end to the other and maybe some of this picnic will take place in the grounds of the observatory in Paris.

This might be a big deal for the world's astronomers, so the thing to remember is that the Méridian de Paris' also runs through the centre of the Luxembourg Gardens and - who knows? - maybe for this one day everybody will be permitted to eat on the grass there. Let's hope so.

Observatoire de Paris - 61. Avenue de l'Observatoire, 75014 Paris. Métro: Denfert-Rochereau, Saint-Jacques or RER station Port Royal. Guided visits, by reservation only, on the first Saturdays on the month. Closed during school holidays. Info. Tel.: 01 40 51 22 21 and fax.: 33 1 43 54 18 04.

*Tech Note: for the degree sign, it is possible to set 48º50'11" for Windows and 48ö50'11" for Macs; but not for both systems at the same time.- The Geek.

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