firmness vs infirmity

firmness

noun
  • security; steadfastness; good grip 

  • strictness; mental strength 

  • physical durability; rigidness (of material) 

infirmity

noun
  • feebleness, frailty or ailment, especially due to old age. 

  • a moral weakness or defect 

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