harbinger vs herald

harbinger

verb
  • To announce or precede; to be a harbinger of. 

noun
  • A person or thing that foreshadows or foretells the coming of someone or something. 

herald

verb
  • To proclaim or announce an event. 

  • To greet something with excitement; to hail. 

noun
  • A harbinger, giving signs of things to come. 

  • A handbill consisting of an advertisement. 

  • An official whose speciality is heraldry, especially one between the ranks of pursuivant and king-of-arms. 

  • A messenger, especially one bringing important news. 

  • A moth of the species Scoliopteryx libatrix. 

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