doubt vs mirth

doubt

verb
  • To be undecided about; to lack confidence in; to disbelieve, to question. 

noun
  • Disbelief or uncertainty (about something); (countable) a particular instance of such disbelief or uncertainty. 

mirth

noun
  • The emotion usually following humour and accompanied by laughter; merriment; jollity; gaiety. 

  • That which causes merriment. 

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