helix vs incurvature

helix

noun
  • A curve on the surface of a cylinder or cone such that its angle to a plane perpendicular to the axis is constant; the three-dimensional curve seen in a screw or a spiral staircase. 

  • A small volute under the abacus of a Corinthian capital. 

  • The incurved rim of the external ear. 

  • An upside down midair 360° spin in playboating. 

verb
  • To form or cause to form a helix. 

incurvature

noun
  • curvature; curving 

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