magnifying glass vs speculum

magnifying glass

noun
  • An instrument made of convex glass, used to magnify. 

speculum

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

  • 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 mirror, especially one used in a telescope. 

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