ball lightning vs fireball

ball lightning

noun
  • A short-lived glowing ball sometimes observed to float in the air and thought to consist of ionized gas associated with thunderstorms. 

fireball

noun
  • A ball of fire, especially one associated with an explosion. 

  • A charge made of a disc-shaped bomb shell, with four sets of flames, at the top, bottom and on either side. 

  • A class of sailing dinghy with a single trapeze and a symmetrical spinnaker, sailed by a crew of two. 

  • A ball filled with combustibles to be thrown among enemies. 

  • A meteor bright enough to cast shadows. 

  • A feisty, strong-willed person. 

verb
  • To attack with balls of fire. 

  • To explode in a ball of flame. 

  • To pitch the ball very fast. 

How often have the words ball lightning and fireball occurred in a corpus of books? (source: Google Ngram Viewer )