declination vs plummeting

declination

noun
  • At a given point, the angle between magnetic north and true north. 

  • A refusal. 

  • At a given point, the angle between the line connecting this point with the geographical center of the earth and the equatorial plane. 

plummeting

noun
  • A violent or dramatic fall. 

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