"keen, collected calmness of despair. ..."
See in text (The Pit and the Pendulum)
The phrase “keen, collected calmness of despair” describes how, amid the terror, the narrator finds comfort in distress. He is so terrified, that death would almost be more welcome than continued torture. However, readers know that despite his wish to die, he will survive his torture, as the narrator lays out in the beginning of the story. The potential of death, nevertheless, creates an ominous, foreboding tone.