bass viol vs bull fiddle

bass viol

noun
  • A fretted, bowed, stringed musical instrument from the viola da gamba family. It occupies the bass range and is the lowest instrument in the family. Similar to (but smaller than) a cello. 

bull fiddle

noun
  • A double bass (lowest-pitched of instruments of violin family). 

How often have the words bass viol and bull fiddle occurred in a corpus of books? (source: Google Ngram Viewer )