dumbwaiter vs escalator

dumbwaiter

noun
  • A small elevator used to move food etc. from one floor of a building to another. 

escalator

noun
  • An escalator clause. 

  • A motor-driven mechanical device consisting of a continuous loop of steps that automatically conveys people from one floor to another. 

  • Anything that escalates. 

  • An upward or progressive course. 

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