icicle vs watch glass

icicle

noun
  • A drooping, tapering shape of ice. 

watch glass

noun
  • A sandglass. 

  • An item of glass laboratory equipment consisting of a simple, slightly concave circle of glass. It is a general utility item, used to hold small samples, to evaporate liquids, to cover a beaker, and so on. 

  • The glass covering of the face of a watch. 

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