nightstick vs shillelagh

nightstick

noun
  • A long narrow pole-like club carried by police and security personnel, for use in self-defense. 

shillelagh

noun
  • A wooden (traditionally blackthorn (sloe) wood) club ending with a large knob. 

  • Any cudgel, whether or not of Irish origin. 

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