gravity bong vs meerschaum

gravity bong

noun
  • A homemade device used to smoke marijuana, consisting of a plastic jug with the bottom cut out and immersed in a vat of water, which is then raised to create a vacuum beneath its bowl of lit marijuana. 

  • Synonym of waterfall bong 

meerschaum

noun
  • A smoking-pipe made from meerschaum. 

  • A soft white mineral, chiefly used for smoking-pipes and cigar holders. 

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