free space vs vacuity

free space

noun
  • vacuum; a space free of matter. 

  • Used other than figuratively or idiomatically: see free, space. 

vacuity

noun
  • Physical emptiness, an absence of matter; vacuum. 

  • Idleness; listlessness. 

  • Emptiness. 

  • An empty or inane remark or thing. 

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