tropic vs turning circle

tropic

noun
  • Either of the two parallels of latitude 23°27′ north and south of the equator; the farthest points at which the sun can be directly overhead; the boundaries of the torrid zone or tropics. 

adj
  • Of, or relating to the tropics; tropical. 

  • Having the quality of indirectly inducing a biological or chemical change in a system or substrate. 

  • Pertaining to, involving, or of the nature of a trope or tropes. 

  • Hot and humid. 

turning circle

noun
  • The circular path formed by the wheel furthest from the centre of the turn when turning to the maximum extent. 

  • The path followed by a vessel’s center of gravity when it makes a complete turn of 360° with a consistent rudder angle. (FM 55-501) 

  • A place where a vehicle can turn and face in the opposite direction. 

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