ataraxy vs imperturbability

ataraxy

noun
  • State of psychological calm and tranquility, absence of discomfort, or metabolical inactivity. 

  • Ataraxia; freedom from mental disturbance; imperturbability, dogged indifference. 

imperturbability

noun
  • A state of calm, unruffled self-assurance; aplomb, composure. 

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