firmness vs steadfastness

firmness

noun
  • strictness; mental strength 

  • security; steadfastness; good grip 

  • physical durability; rigidness (of material) 

steadfastness

noun
  • Loyalty in the face of trouble and difficulty. 

  • Steadfast resolution. 

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