declination vs incline

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. 

incline

noun
  • A slope. 

  • A portal of a subway tunnel. 

verb
  • To bend or move (something) out of a given plane or direction, often the horizontal or vertical. 

  • To tend to do or believe something, or move or be moved in a certain direction, away from a point of view, attitude, etc. 

  • To slope. 

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