introspection vs meditation

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 

meditation

noun
  • A devotional exercise of, or leading to contemplation. 

  • A contemplative discourse, often on a religious or philosophical subject. 

  • Careful and thorough thought. 

  • A musical theme treated in a meditative manner. 

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