unimpressibility

His perfect self-possession and coolness, the _nil-admirari_ and _nil-agitari_ atmosphere which surrounded him, excited my admiration at first, till I discovered that it arose, not from the composure of a mind too deep-rooted to be swayed by external circumstances, but rather from a peculiar hardness and unimpressibility of temperament that kept him on the same level all the time.

The Atlantic Monthly, Volume 05, No. 30, April, 1860 Various

It was about this moment when Rübetsahl began to discover that he had mistaken the tall, gray-eyed girl with whom he was talking; that her coldness was rather a transparent purity like that of star-beams which seem cold to the hand but warm to the soul, and that her apparent unimpressibility was rather the veiled impressibility of an enthusiasm which was so strong that it feared itself.

Tiger-Lilies. A Novel. 1867

His perfect self-possession and coolness, the nil-admirari and nil-agitari atmosphere which surrounded him, excited my admiration at first, till I discovered that it arose, not from the composure of a mind too deep-rooted to be swayed by external circumstances, but rather from a peculiar hardness and unimpressibility of temperament that kept him on the same level all the time.

Found and Lost 1860

His perfect self-possession and coolness, the nil-admirari and nil-agitari atmosphere which surrounded him, excited my admiration at first, till I discovered that it arose, not from the composure of a mind too deep-rooted to be swayed by external circumstances, but rather from a peculiar hardness and unimpressibility of temperament that kept him on the same level all the time.

Found and Lost Anonymous 1860

a transparent purity like that of star-beams which seem cold to the hand but warm to the soul, and that her apparent unimpressibility was rather the veiled impressibility of an enthusiasm which was so strong that it feared itself.

Tiger-lilies 1867