preserve vs vary

preserve

verb
  • To maintain throughout; to keep intact. 

  • To save from decay by the use of some preservative substance, such as sugar or salt; to season and prepare (fruits, meat, etc.) for storage. 

  • To protect; to keep from harm or injury. 

noun
  • An activity with restricted access. 

  • A sweet spread made of any of a variety of fruits. 

  • A reservation, a nature preserve. 

vary

verb
  • Not to remain constant: to change with time or a similar parameter. 

  • To make of different kinds; to make different from one another; to diversity; to variegate. 

  • To embellish; to change fancifully; to present under new aspects, as of form, key, measure, etc. See variation. 

  • To be or act different from the usual. 

  • To institute a change in, from a current state; to modify. 

  • To change with time or a similar parameter. 

  • To display differences. 

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