By Zimmermann, in my French translation:
On a dit avec raison que les savants astreints à une existence solitaire, et occupés de graves travaux, ne peuvent avoir ni la gaieté d’esprit, ni l’élégance de manières, ni la vivacité d’entretien des personnes qui vivent habituellement dans le monde et qui en connaissent tous les usages.
It is clear that a man with habits so rare and so contrasting with those of ordinary men will show himself, by his own behavior, to be essentially different. The reclusive man, accustomed to silence and deep meditation, molds himself to find the agitation of common surroundings progressively inhospitable. It is natural that he completely loses that expansiveness, that sociability commonly referred to as “good manners”. These, by the way, can only cause him disgust and astonishment. It all boils down to a matter of habits: like it or not, these are what will define, over time, what a man is.