Any man or woman, in any age and under any circumstances, who will, can live the heroic life and exercise heroic influences.

It is of the essence of self-sacrifice, and therefore of heroism, that it should be voluntary; a work of supererogation, at least, towards society and man; an act to which the hero or heroine is not bound by duty, but which is above though not against duty.

Lecture on Heroism. 1872.