personification vs unknown quantity

personification

noun
  • A person, thing or name typifying a certain quality or idea; an embodiment or exemplification. 

  • An artistic representation of an abstract quality as a human 

  • A literary device in which an inanimate object or an idea is given human qualities. 

unknown quantity

noun
  • A person or thing whose nature or value is a mystery. 

  • Used other than figuratively or idiomatically: see unknown, quantity. 

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