Meanings of impressively solemn in English

Then he heard singing; and listening, never had human voices seemed to him so impressively solemn.

Only,"-herehis voice became impressively solemn,-"onlyyou mustn't ever tell how much you really did pay."

But," she added, and her voice was impressively solemn, "heaven help any one of us who gets in the path of the falls."

Dr. Smith declares the treatise to have been well and thoroughly argued, sometimes most impressively solemn, at others keenly sarcastic, and spirited and fearless throughout.