hark back vs regress

hark back

noun
  • 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). 

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

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

  • To call back (hounds); to recall. 

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

regress

noun
  • The act of passing back; passage back; return; retrogression. 

  • In property law, the right of a person (such as a lessee) to return to a property. 

  • The power or liberty of passing back. 

verb
  • To move backwards to an earlier stage; to devolve. 

  • To move from east to west. 

  • To perform a regression on an explanatory variable. 

  • To interrogate a person in a state of trance about forgotten elements of their past. 

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