placation vs propitiation

placation

noun
  • A process or act of placating; appeasement or an expression of appeasement. 

propitiation

noun
  • The act of propitiating; placation, atonement, similar to expiation but with the added concept of appeasement of anger. 

  • The death of Christ as a basis for the forgiveness of sin. 

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