introspection vs musing

introspection

noun
  • A looking inward; specifically, the act or process of self-examination, or inspection of one's own thoughts and feelings; the cognition which the mind has of its own acts and states 

musing

noun
  • thought, meditation, contemplation 

adj
  • Absorbed in thought; contemplative 

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