come across vs stumble upon

come across

verb
  • To find, usually by accident. 

  • To produce what was desired; come up with the goods. 

  • To give an appearance or impression; to project a certain image. 

  • To change sides; to cross over to work for the opposition. 

  • Used other than figuratively or idiomatically: see come, across. 

stumble upon

verb
  • To discover or find something by accident. 

  • To meet somebody by chance. 

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