imperturbableness

a certain degree of mental repose -- or what may possibly be called imperturbableness -- is necessary to influence.

Lessons in Life A Series of Familiar Essays Timothy Titcomb

The poor, odious figment that baptism with the blood of Christ is the sole entrance to heaven, is rebuked by the sweet and awful imperturbableness with which the laws of being act, distributing the ingredients of hell or heaven to every one accordingly as his vices disobey or his virtues obey the will of God.

The Destiny of the Soul A Critical History of the Doctrine of a Future Life William Rounseville Alger 1863

I had nothing in my favour to balance this, but a sort of constitutional equanimity and imperturbableness of temper, which, if I was at any time silenced, made me not look like a captive to be dragged at the chariot-wheels of my adversary.

Thoughts on Man: His Nature, Productions, and Discoveries 1831

But happiness consists in imperturbableness of spirit, that is, in suspense of judgment; and as it is our duty to promote our own happiness, it is our duty to live without desire or fear, preference or abhorrence, love or hatred, in entire apathy, — a life of which Mohammed’s fabled coffin is the fittest symbol.

A Manual of Moral Philosophy 1852