incantation vs spells

incantation

noun
  • Any esoteric command or procedure. 

  • A formula of words used as above. 

  • The act or process of using formulas and/or usually rhyming words, sung or spoken, with occult ceremonies, for the purpose of raising spirits, producing enchantment, or creating other magical results. 

spells

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