investigation vs wringer

investigation

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

wringer

noun
  • One who wrings. 

  • A device for drying laundry consisting of two rollers between which the wet laundry is squeezed (or wrung); a mangle. 

  • Something that causes pain, hardship, or exertion; an ordeal. 

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