feather one's nest vs richen

feather one's nest

verb
  • To achieve benefits, especially financial ones, by taking advantage of the opportunities with which one is presented; to amass a comfortable amount of personal wealth. 

richen

verb
  • To make or render rich or richer. 

  • To become rich or richer; become superior in quality, condition or effectiveness. 

  • To gain richness; become heightened or intensified in brilliancy. 

How often have the words feather one's nest and richen occurred in a corpus of books? (source: Google Ngram Viewer )