pier glass vs speculum

pier glass

noun
  • A tall narrow mirror, usually set between two windows, above a pier table. 

speculum

noun
  • A mirror, especially one used in a telescope. 

  • A lookout place. 

  • A bright, lustrous patch of colour found on the wings of ducks and some other birds, usually situated on the distal portions of the secondary quills, and much more brilliant in the adult male than in the female. 

  • A medical instrument used during an examination to dilate an orifice. 

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