continual vs flash in the pan

continual

adj
  • Recurring in steady, rapid succession. 

  • Seemingly continuous; appearing to have no end or interruption. 

  • Forming a continuous series. 

flash in the pan

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

  • A transient occurrence with no long-term effect. 

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