declination vs inclination

declination

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

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

  • A refusal. 

inclination

noun
  • The angle of intersection of a reference plane 

  • A tendency. 

  • A physical tilt or bend. 

  • A slant or slope. 

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