inflexibleness vs solidity

inflexibleness

noun
  • The quality or state of being inflexible 

  • Obstinacy of will or temper; firmness of purpose that will not yield to importunity or persuasion; unbending pertinacity. 

solidity

noun
  • The state or quality of being solid. 

  • Moral firmness; validity; truth; certainty. 

  • The solid contents of a body; volume; amount of enclosed space. 

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