publication vs third class

publication

noun
  • An issue of printed or other matter, offered for sale or distribution. 

  • The act of publishing printed or other matter. 

  • The communication of information to the general public etc. 

third class

noun
  • A reduced-rate mail service for printed matter. 

  • The cheapest accommodation on a train or ship. 

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