john vs thunderbox

john

noun
  • A device or place to urinate and defecate: now usually a toilet or lavatory, but also (dated) a chamber pot or outhouse. 

  • A male mule. 

  • A Western man traveling in East Asia. 

  • A prostitute's client. 

thunderbox

noun
  • Any lavatory or toilet, especially a rudimentary outdoor latrine or toilet, or an outhouse. 

  • A box of metal balls which is shaken to create a thunder sound effect. 

  • A chamber pot enclosed in a box; a portable commode. 

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