slip away vs vanish into thin air

slip away

verb
  • To disappear; to elude one; to recede; to dwindle. 

  • To leave a place, or a gathering, without being noticed. 

  • To die peacefully. 

  • To pass quickly, almost unnoticed. 

vanish into thin air

verb
  • To disappear in a mysterious way. 

How often have the words slip away and vanish into thin air occurred in a corpus of books? (source: Google Ngram Viewer )