friar's lantern vs ignis fatuus

friar's lantern

noun

  • ignis fatuus; will o' the wisp 

ignis fatuus

noun

  • A will o' the wisp. 

  • A delusion, a false hope. 

How often have the words friar's lantern and ignis fatuus occurred in a corpus of books? (source: Google Ngram Viewer )