armonica vs glassichord

armonica

noun
  • A musical instrument made of blown-glass bowls mounted on a spindle turned originally by a foot pedal, and played with wetted fingers, producing an ethereal sound. Technically, it is a crystallophone. 

glassichord

noun
  • A 19th-century musical instrument made of glass plates that are struck by hammers or sticks. 

  • Synonym of glass harmonica 

  • Anything that produces a similarly pure continuous sound. 

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