bass viol vs upright bass

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. 

upright bass

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

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