peroration vs swan song

peroration

noun
  • A discourse or rhetorical argument in general. 

  • The concluding section of a discourse, either written or oral, in which the orator or writer sums up and commends his topic to his audience, particularly as used in the technical sense of a component of ancient Roman oratorical delivery. 

swan song

noun
  • A final performance or accomplishment, especially one before retirement. 

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