bowls vs rugby ball

bowls

noun
  • A ball used in the game of bowls 

  • A precision sport where the goal is to roll biased balls (weighted on one side, and called bowls) closer to a smaller white ball (the jack or kitty) than one's opponent is able to do. 

rugby ball

noun
  • A spheroidal ball designed for the sport of rugby. 

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