incontinence vs mercifulness

incontinence

noun
  • The inability of any of the physical organs to restrain discharges of their contents; involuntary discharge or evacuation (of urine or feces). 

mercifulness

noun
  • The state of being merciful; mercy. 

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