ardor vs enthusiasm

ardor

noun
  • Spirit; enthusiasm; passion. 

  • Intense heat. 

  • Great warmth of feeling; fervor; passion. 

enthusiasm

noun
  • Intensity of feeling; excited interest or eagerness. 

  • Something in which one is keenly interested. 

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