sangfroid vs serenity

sangfroid

noun
  • Composure, self-possession or imperturbability especially when in a dangerous situation. 

serenity

noun
  • A lack of agitation or disturbance. 

  • The state of being serene; calmness; peacefulness. 

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

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