flash in the pan vs momentary

flash in the pan

noun
  • A career notable for early success not followed by significant accomplishment. 

  • A transient occurrence with no long-term effect. 

momentary

adj
  • Lasting for only a moment. 

  • Ephemeral or relatively short-lived. 

  • Happening at every moment; perpetual. 

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