precation vs rogation

precation

noun
  • A prayer or act of praying; an earnest request. 

rogation

noun
  • A deeply serious and somber prayer or entreaty. 

  • The demand, by the consuls or tribunes, of a law to be passed by the people; a proposed law or decree. 

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