LOFT vs dripstone

LOFT

noun
  • loss of fluid test 

dripstone

noun
  • Stalactites and stalagmites collectively. 

  • A protective moulding over a door or window that allows rain to drip away from the structure. 

  • A water filter in which impurities are removed by running water through a porous stone. 

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