second class vs third class

second class

noun
  • A class of postage with delivery times slower than first class. 

  • A class of travel, inferior to first class. 

  • The second-lowest rank in the Boy Scouts of America, between tenderfoot and first class. 

third class

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

  • The cheapest accommodation on a train or ship. 

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