atheling vs earl

atheling

noun
  • A prince, especially an Anglo-Saxon prince or royal heir. 

earl

noun
  • A British or Irish nobleman next in rank above a viscount and below a marquess; equivalent to a European count. A female using the style is termed a countess. 

  • Any of various nymphalid butterflies of the genus Tanaecia. Other butterflies in this genus are called counts and viscounts. 

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