Hosts loved to detain the dry lawyer, when the light-hearted and the loose-tongued had already their foot on the threshold; they liked to sit a while in his unobtrusive company, practising for solitude, sobering their minds in the man's rich silence after the expense and strain of gaiety.
There are no more uses of "sobering" identified with this meaning, but check unspecified meaning below.
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These are sobering statistics that should leave all of us concerned.
She stopped laughing and said in a sober tone, ...
It was his custom of a Sunday, when this meal was over, to sit close by the fire, a volume of some dry divinity on his reading-desk, until the clock of the neighbouring church rang out the hour of twelve, when he would go soberly and gratefully to bed.
His past was fairly blameless; few men could read the rolls of their life with less apprehension; yet he was humbled to the dust by the many ill things he had done, and raised up again into a sober and fearful gratitude by the many that he had come so near to doing, yet avoided.
…had thus, from the first moment of his entrance, struck in me what I can only describe as a disgustful curiosity) was dressed in a fashion that would have made an ordinary person laughable; his clothes, that is to say, although they were of rich and sober fabric, were enormously too large for him in every measurement—the trousers hanging on his legs and rolled up to keep them from the ground, the waist of the coat below his haunches, and the collar sprawling wide upon his shoulders.