dulcimer vs guqin

dulcimer

noun
  • A stringed instrument, with strings stretched across a sounding board, usually trapezoidal, played by plucking on the strings (traditionally with a quill) or by tapping on them (in the case of the hammer dulcimers). 

guqin

noun
  • A plucked zither-like stringed instrument (chordophone), traditionally featuring seven unfretted strings, originating in ancient China. 

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