allay vs spark off

allay

noun
  • Alleviation; abatement; check. 

verb
  • To make quiet or put at rest; to pacify or appease; to quell; to calm. 

  • To alleviate; to abate; to mitigate. 

spark off

verb
  • To initiate something by providing the necessary conditions. 

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