Robert-Aglaé CAUCHOIX (1776-1845), optician, manufacturer of astronomical glasses, he worked with Jean-Baptiste Biot on polarization.
Autograph letter signed to the bishop of Cambrai. 2 pp. in-4. [Paris], November 20, 1811. Address on the back with postmark.
Beautiful and rare scientific letter. His occupations and "the new disposition of my workshops" did not allow him to communicate to him the curves "which succeeded me in the three-glass lenses with the flint glass of Mr d'Artigues []. I hope that this letter will arrive in time to find several unworked pieces, on which you can, if you deem it appropriate, apply the means I have used. The dimensions which served me in the objectives of 45 lines of diameter and 42 inches of focus with three glasses are these reduced for a focus =1000
Crown : 1st face towards the object +429 ; 2nd face +809
Flint : 3rd side towards the object -429 ; 4th side -519
Crown: 5th face towards the object +643; 6th face towards the eyepiece +643
The crown-glass is made of ice from Cherbourg or Tour-la-Ville.
He also gives the results for a 4 inch objective and 5 feet of focus. "These are the curvatures that have worked for me, and that I gave myself at the time. I told you that Mr. Biot was looking for more perfect ones, but he has not yet finished his work []".
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