invention vs masterwork

invention

noun
  • The capacity to invent. 

  • Something invented. 

  • The act of inventing. 

  • A small, self-contained composition, particularly those in J.S. Bach’s Two- and Three-part Inventions. 

masterwork

noun
  • A piece done to prove possession of skill sufficient to be ranked a master. 

  • A piece of quality, indicative of having been made by a master; a masterpiece. 

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