glimpse vs observation post

glimpse

noun
  • A brief look, glance, or peek. 

  • A sudden flash. 

  • A faint idea; an inkling. 

verb
  • To see or view briefly or incompletely. 

  • To appear by glimpses. 

observation post

noun
  • a lookout or vantage point 

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