Henri DUVEYRIER (1840-1892), traveler, explorer... - Lot 247 - Conan Belleville Hôtel d'Ainay

Lot 247
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Henri DUVEYRIER (1840-1892), traveler, explorer... - Lot 247 - Conan Belleville Hôtel d'Ainay
Henri DUVEYRIER (1840-1892), traveler, explorer and geographer. 4 autograph letters signed to the astronomer Ernest Mouchez. 10 pp. in-8. Sèvres, January 1888 - Nov. 1889. Interesting scientific correspondence, rectifying geographical maps from surveys made in North Africa. "For the latitude there are 36 circummeridian heights of the sun, taken on December 9-10 (16 heights) and December 15-16 (20 heights). For the longitude: a distance from the edge of the moon to the Epi of Virgo, framed by heights from the moon to the star. This observation is from December 9 [...]. Although there was only one lunar distance observed, it will give I hope a more exact longitude than the one we have: the angles were measured to the nearest 5'' [...]. In calculating my observations Mr. Oltramare found for the latitude [of Fez] 34°4'13'' N. or two minutes less than Ali Bey. And I can vouch for my observations to within a small fraction of a minute. This leads me to doubt the longitude given under the name of Ali Bey [...]. Do you accept the correction of the longitude of the mouth of the Ouâd Kis (western border of Algeria) indicated, after the fact, on the last prints of the marine chart n°3412 (from the Zafarines islands to the mouth of the Tafna) [...]. Finally, what approximation of accuracy would you give to the position of the mouth of the Moloûya? Has this point been recognized? My route from Tlemcen to Melika is shown on a projection, to the scale of my drawing (1/100,000°), and the coastline should be marked there as well [...]. To the west of the cape, at the bottom of the gulf formed by the promontory of the Three Forks, my route would place the sea a little further north than on map no. 1711. However, I raised my route step by step, and it falls well on the mouth of the Ouâd Kis and on Meliba. Perhaps the discrepancy that I notice to the west of Cape del Agua is the result of local magnetic attractions? But then the compasses of the lighthouse will have been subjected to them like mine [...]".
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