Source: Nouveau Systême de Musique Theorique (Paris: 1726)
Original text
Thomas Dent’s annotated extraction of the relevant passages

Compared to the concise and straightforward descriptions of D’Alembert and Rousseau, Rameau’s description of a “tempérament ordinaire” is lengthy and convoluted. Therefore, it is open to considerable interpretation in its precise details, and every modern author may well have his or her own vision, depending on their theoretical and musical, experience with other texts, temperament theory in general, etc. I present two versions here, one of my own as well one by Mark Lindley.

Rameau's mollified meantone Poletti

Rameau's mollified meantone Lindley