calmness vs self-possession

calmness

noun
  • The product of being calm. 

  • The state of being calm; tranquillity; silence. 

self-possession

noun
  • calmness and composure, especially when under stress 

  • confidence in one's own powers 

How often have the words calmness and self-possession occurred in a corpus of books? (source: Google Ngram Viewer )