bush telegraph vs rumor mill

bush telegraph

noun
  • A gossip network. 

  • A system used by undeveloped societies in remote regions for communication over long distances, such as drum sounds, word-of-mouth relay, or smoke signals. 

rumor mill

noun
  • A process in which a group or network of persons originate or promulgate gossip and other unsubstantiated claims. 

How often have the words bush telegraph and rumor mill occurred in a corpus of books? (source: Google Ngram Viewer )