Besterman indicates letter was probably written in France or Belgium, sometime in the spring or summer of 1748. --Cf. Besterman, v. 2, p. 199.
Part of a large collection of letters from Madame du Châtelet to the Marquis de Saint Lambert, Charles Augustin de Ferriol, comte d'Argental, the Marquise de Boufflers, the Duc de Richelieu and others. Items in the collection are described in separate records; see MA 2287 for more information.
Wondering why he is not visiting her while he can in all decency; saying that he loves her less; asking him to come at once if he loves her because she is feeling very ill.