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Joel Kovarsky wrote:
On 4/11/2010 3:00 AM, David Bradbury wrote:
So the question is- did De Fer, working at about the same time as the
Cassinis, under French royal patronage, and having access to the
Picard data, make use of it to define his League by reference to the
Earth's circumference? Perhaps measurement on the map itself, between
points which are likely to have been positioned with maximum
accuracy, can help provide an answer.
It is unlikely that a variable measure like a one-hour walking
distance would be standardized to the same level as the consistent
beat of a pendulum, although anything is possible. I may be wrong, but
do not think the one-hour walking distance scale appeared on the
Cassini maps of France. I believe the 1:86,400 scale of the 180 sheet
map published between 1798-1812 was still based on the old English
fathom (and not yet the pendulum swing):
http://www.informatics.org/france/maps.html .
The "lieue commune" is defined as "deux mille deux cens quatre vingt
deux toises" or as "vingt-cinq lieues au degré" in the "Nouveau
dictionnaire de l'Académie française," published in 1718, so clearly the
concepts which would lead to the precise definitions later used were
understood in academic circles by that time. Still, it would be best to
gather some hard evidence from maps of the era, unless somebody can
point us to where that has already been done.
David Bradbury
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