enquiring vs investigation

enquiring

noun
  • An instance of making an enquiry; an asking. 

adj
  • Curious, inquisitive or investigative. 

investigation

noun
  • The act of investigating; the process of inquiring into or following up; research, especially patient or thorough inquiry or examination 

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