assuage vs pour oil on troubled waters

assuage

verb
  • To pacify or soothe (someone). 

  • To lessen the intensity of, to mitigate or relieve (hunger, emotion, pain etc.). 

pour oil on troubled waters

verb
  • To calm, appease or quieten a person or situation. 

How often have the words assuage and pour oil on troubled waters occurred in a corpus of books? (source: Google Ngram Viewer )