leading-edge vs on the line

leading-edge

adj
  • Of or pertaining to the leading edge of an airfoil 

  • leading, latest or most up-to-date 

on the line

prep
  • At risk, as in a contest or enterprise. 

  • Currently calling on the telephone. 

  • On one of the lines marked on a playing field or court; (by extension) within bounds. 

  • On a level with the eye of the observer, as of a picture hung in on a wall. 

How often have the words leading-edge and on the line occurred in a corpus of books? (source: Google Ngram Viewer )