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  Here is my translation from the Russian translation
of a page from the book of Bougainville, (Paris, 1671)..
He is talking about a fix
by Lunar distances with the error of about 3.5'.
(Which implies at most
10" error in the measurement of the distance itself).
This is with a Hadley octant made of wood:-)
Can someone verify the precision of his fix with a modern map
and comment this text?
(Don't forget he is using Paris meridan as zero!)
The cape of Vierges
is called Cabo de las Virgenes now.
It is near the entrance to the Magellan strait.
I cite:

"This fix, combined with bearings gives the following
coordinates for the cape of Vierges:
Lat. S 52d23' and Long. 71d25'20" West of Paris.
Because the cape of Vierges is an interesting point
for geography, I have to explain what made me believe
that its position was fixed by me with almost
absolute precision.

"On November 27, afternoon, Chevalier du Bouchage measured
eight Lunar distances whose averaging gave the
longitude of 65d0'30'' (West of Paris) at 1h43m26s of
real time; M. Verron on his side measured 5 lunar distances,
whose average gave our longitude at the same time as
64d57'. The weather was good and favorable for observations.
On 29-th at 3h57m35s of true time, M. Verron, by 5-fold
measurement of Lunar distances found the longitude as 67d49'30"
(West of Paris).

"Now, having found the place of the ship in view of cape Vierge,
and taking as a basis [for dead reckoning - A. E.]
the longitude determined
on November 27,
by averaging the results of observations of
Chevalier du Bouchage, and M. Verron, we will obtain that
the cape of Vierge is placed on the longitude 71d29'42" W of Paris.
Obserevations at the moment of determination by bearings
of position of cape Vierge would give the result of 38'47" more
to the West. However, I suppose that one has rather to take as a base
the observations of Nov. 27, because they were made several times,
by two observers who did not communicate with each other,
while their results differ only by 3'30", and seem so plausible
that it is hard to reject them.

"These observations were made using an English octant.
The method of determining longitude in sea
by way of Lunar distances to the Sun
or to Zodiac stars is known for many years.
Mr. de la Caille and  d'Apres, used this method in the sea,
also with the Hadley octant."

Alex.

   

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