but there's no way that a man of his era (c. 1700) would have referred to himself in the feminine gender: therefore, it is a quote from an earlier work, Which one?
That is a wrong prejudice, I'd say...
Men of that time were actually less confused by the clear distinction between grammatical gender and sex... than are our contemporaries.
French monarchs of this era commonly referred to themselves in the feminine gender, for example, not because they did feel they would be women or ladies, but because the subject of their sentence,
majesté is feminine, so every pronoun, adjective and participle of the sentence had to agree with it.
Men of that time were also referred in the feminine gender by their interlocutors. The Canadian Pierre du Calvet wrote to George III: «
Les nôtres ont depuis longtemps prononcé en faveur de Votre Majesté : Elle met sa gloire à être le père de ses sujets : Elle n’estime dans la royauté que le pouvoir qu’elle Lui donne de faire des heureux. La clémence, l’humanité, l’amour de la justice et des lois, toutes les vertus règnent avec Elle sur le trône. La reconnaissance publique se charge de transmettre à la postérité, le nom de Votre Majesté, avec tous les transports de l’admiration et de l’amour. »
