hark back vs turn back

hark back

verb
  • To return to where one has previously been; to retrace one's steps. 

  • To allude, return, or revert (to a subject previously mentioned, etc.); also, to evoke, or long or pine for (a past era or event). 

  • To call back (hounds); to recall. 

  • Of hounds: to retrace a course in order to pick up the lost scent of prey. 

noun
  • An act of hounds retracing a course in order to pick up the lost scent of prey. 

  • An act of alluding, returning, or reverting (to a subject previously mentioned, etc.); also, an act of evoking, or longing or pining for (a past era or event). 

turn back

verb
  • To reverse direction and retrace one's steps. 

  • To cause to reverse direction and retrace one's steps. 

  • To return to a previous state of being. 

  • To prevent or refuse to allow passage or progress. 

  • To adjust to a previous setting. 

  • To fold something back; to fold down. 

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