refer vs touch upon

refer

noun
  • A blurb on the front page of a newspaper issue or section that refers the reader to the full story inside the issue or section by listing its slug or headline and its page number. 

verb
  • To point to either a specific location in computer memory or to a specific object. 

  • To mention (something); to direct attention (to something) 

  • To submit to (another person or group) for consideration; to send or direct elsewhere. 

  • To make reference to; to be about; to relate to; to regard; to allude to. 

  • To place in or under by a mental or rational process; to assign to, as a class, a cause, source, a motive, reason, or ground of explanation. 

  • Required to resit an examination. 

  • To be referential to another element in a sentence. 

  • To direct the attention of (someone toward something) 

touch upon

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