dissertate vs preach

dissertate

verb
  • To make a dissertation; to discourse. 

  • To write one's dissertation. 

preach

verb
  • To proclaim by public discourse; to utter in a sermon or a formal religious harangue. 

  • To give a sermon. 

  • To advise or recommend earnestly. 

  • To teach or instruct by preaching; to inform by preaching. 

  • To give advice in an offensive or obtrusive manner. 

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