bass guitar vs euphonium

bass guitar

noun
  • A long-necked and solid-bodied stringed instrument (chordophone), tuned to produce bass or low notes, usually with a fretted fingerboard and four thick strings, and requiring the use of an amplifier. 

euphonium

noun
  • A valved brass instrument with conical tubing similar in appearance to a tuba but of higher pitch; a sax horn. 

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