Breaking radio silence after some years …
This is a follow-up to the unresolved discussion in this old thread from late 2007. In which I took the opportunity to observe that the Paris Meridian (the N-S line that was originally used to define the metre) was oddly exactly visible as a lengthy narrow discolouration in the grass on the Google Maps images of Parc Montsouris, about a mile south of the Paris Observatory - at this location; the lawn in question is the large oval one in the NW corner of the park. (The anomaly is sort of arguably still visible in the current Google Maps imaging, but you have to know where to look. To see the clearest images of it, see the comments about Google Earth below. For the exact path of the meridian across the city, see this page.) Some useful observations were made in the thread by Antonius Block, but the mystery was not settled.
As mentioned at the time, expecting that any discolouration was most likely to be most visible on the ground during the summer, the vague plan was to look at the lawn in the summer of 2008. Well, life intervened and, one way or another, that plan fell through. After a period of regular trips to the city, I then didn’t find myself back in Paris until last week. Amongst other distractions, a swing past Parc Montsouris was in order.
To reiterate various basic points, I’ll note that there is a monument in the park - the Mire du Sud - that was erected to mark the meridian, but that this was subsequently moved a hundred feet or so to the east. The reason for putting this in the park in the first place was that the ridgetop at its southern edge, which now coincides with the Périphérique, meant that this was the southern extremity of the meridian directly observable from the Observatory. (There’s a matching Mire du Nord atop the northern horizon in Montmartre.)
Ignore Dan Brown completely, for reasons explained in the previous thread.
So what is visible on the grass on a day in late May in 2014? Conditions were less than ideal. It’s been a warm and wet spring in London and probably so in Paris as well. Furthermore, the weather was showery and it’d already rained in the park on the day that I visited. So the grass wasn’t dried out. Between prior research and the Arago medallions (see below), it was easy enough to get an exact alignment of the meridian across the lawn. And …
Nothing stood out. At all. Not from the bottom of the slope, not from the top, not from the side and especially not from close up. Now a look at the grass did reveal that it’s much rougher and less manicured than I’d remembered it from the last time I visited. There are even patchy holes in bits of it. It’s just that these don’t particularly align with the meridian.
There has however been incremental progress on other fronts. It’ll be useful to consider this in terms of the different hypotheses that were floated in 2007.
[ul]It seemed possible that some earlier landscaping in the park had included a path deliberately aligned with the (previously defined) meridian. The discolouration was then a form of archaeological “crop marks” tracing whatever the remains of this former path were still beneath the soil. This was my favoured guess at the time, but none of the subsequent evidence stacks up in its favour at all. Digging up old photos of the park does show that there have been significant changes over the years, but not in this area and none of them show any such path. Nor does it show up in old maps of the area - checking the layout of Parc Montsouris has now long been an automatic reaction of mine to any oldish map of Paris. Difficult to rule out entirely, but nope.[/ul]
[ul]“Medallion bagging”. Antonius’s suggestion back in 2007. There were a series of small markers embedded at intervals along the meridian across the city in 1994. (This was partly as a symbolic replacement for the statue of Arago, the 19th century astronomer and politician, that used to stand on the meridian immediately south of the Observatory, but which was destroyed for political reasons during the Occupation. The empty plinth survives.) The suggestion was thus that people were deliberately walking the meridian and this was creating an informal path across the grass. I’m no more convinced by this now than I was then, though there is at least one example of someone trying to find them all. A nice idea, granted. Yet even the guidebook on the line that I mentioned in 2007 seems to have quickly gone out of print and become a secondhand rarity. Not a significant activity. Furthermore, there are no medallions on the lawn itself: all the ones in the park are on the paths.
As an aside, the French collectively planted lots of trees in 2000 to trace the meridian as a gesture to mark the millennium, but this was only done outside of Paris. That does, however, lead to …[/ul]
[ul]The “millennium picnic” in 2000. To celebrate the occasion, the French also held a giant communal picnic along the meridian, all the way across the country, on Bastille Day in 2000. As previously mentioned, I happened to be in Paris on 14th July 2000 and duly saw the version of the picnic mounted in the centre of the city: tables arranged up boulevards that were very, very vaguely in the vicinity of the meridian. Nice as a gesture, but not especially rigorous. However, one advance since 2007 is that Google Earth now has “historical” imagery for the likes of central Paris. The very old layer they have is from 1949: no sign of the anomaly on the grass. (As an incidental observation, it’s commonplace to find good comprehensive series of aerial survey photos from this period, as wartime reconnaissance kit was turned to civilian use and used to cover not just military targets.) Then they have multiple layers for the period 2001 to the present. Now the anomaly comes and goes in these images, presumably partly as a result of seasonal changes and the like. But what really leaps out is that the line is most obvious in the 2001 image.[/ul]
Given the evidence to date, it’s impossible to be conclusive. In particular, I would like to see the equivalent of that 2001 image for some dates in the Nineties. But the suggestion that the anomaly is a result of the picnic in 2000 now seems distinctly plausible. A few hours of people eating and drinking at tables or blankets laid out across the lawn seem to have created a surprisingly narrow disturbance in the grass that was visible years later. The other most useful next step would be photos from the picnic, to judge how closely it followed the meridian in the park. Google Books throws up this image, which doesn’t really help, and that’s about it.
So no final resolution, but some progress.