In the preface to this would-be volume, Rousseau wrote that the Essay was originally meant to be included in the Discourse on Inequality, but was omitted because it "was too long and out of place".
In this text, Rousseau lays out a narrative of the beginnings of language, using a similar literary form as the Second Discourse.
The colder climates of the north, however, stripped language of its passionate characteristic, distorting it to the present rational form.
As the text was initially written in 1754, and was sent to the publisher in 1763, it appears safe to argue that the tensions between the Essay and the Second Discourse were intentional.
The third chapter of Jacques Derrida's Of Grammatology critiques and analyzes Rousseau's essay.