interposition vs mediatorship

interposition

noun
  • The act of interposing, or the state of being interposed; a being, placing, or coming between; mediation. 

  • The thing interposed. 

mediatorship

noun
  • The office or character of a mediator. 

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