self-possession vs serenity

self-possession

noun
  • calmness and composure, especially when under stress 

  • confidence in one's own powers 

serenity

noun
  • The state of being serene; calmness; peacefulness. 

  • A lack of agitation or disturbance. 

  • A title given to a reigning prince or similar dignitary. 

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