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A friend of mine, Rebecca Karo, is an art historian and also works as an archivist in Exeter, NH.  She wrote me with this question:

"The American Independence Museum in Exeter, NH, has a

letter from the Marquis de Condorcet to a royal minister

(I have to find out who) about acquiring 600 copies of

François Coudraye, 'Dissertation sur la manière de

déterminer les longitudes à la mer, couronnée par la

société des arts et métiers d'Utrecht,' 1783. He asked

the minister to also confer with Charles de Borda,

another interesting mariner/mathematician, about acquiring

the book. Condorcet wrote that the book was clear and

methodical and would be good for mariners who are unused

to calculating their position while at sea. The book is

small -- an octavo of 94 pages -- so it would be easy to

take on board!"

Charles de Borda's lunar-distance clearing method is described in the books of Cotter, and he is mentioned in connection with testing chronometers at sea in The Quest for Longitude (William J. H. Andrewes, ed.) and in The Marine Chronometer by Rupert T. Gould.

But I can find very little about François Coudraye, although a page in the French Wikipedia confirms that he wrote the 1783 dissertation on longitude at sea: https://fr.wikipedia.org/wiki/Fran%C3%A7ois-C%C3%A9lestin_de_Loynes_de_La_Coudraye . 

Does anyone here know anything more about François Coudraye (1743-1815) or his 94-page book?

Roger