viola d'amore vs viola da gamba

viola d'amore

noun
  • A 7- or 6-stringed musical instrument similar to the treble viol, used chiefly in the Baroque period. 

viola da gamba

noun
  • Synonym of viol 

How often have the words viola d'amore and viola da gamba occurred in a corpus of books? (source: Google Ngram Viewer )