foray vs incursion

foray

noun
  • A sudden or irregular incursion in border warfare; hence, any irregular incursion for war or spoils; a raid. 

  • A brief excursion or attempt, especially outside one's accustomed sphere. 

verb
  • To participate in a foray. 

  • To do or attempt something outside one's typical area of expertise. 

incursion

noun
  • An aggressive movement into somewhere; an invasion. 

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