life raft vs pram

life raft

noun
  • A usually inflatable raft carried aboard a ship or airplane, used to save lives in case the vessel has to be abandoned in an emergency on the sea. 

pram

noun
  • A type of dinghy with a flat bow. 

  • A small vehicle, usually covered, in which a newborn baby is pushed around in a lying position. 

  • A flat-bottomed barge used on shallow shores to convey cargo to and from ships that cannot enter the harbour. 

  • A similar barge used as platform for cannons in shallow waters which seagoing warships cannot enter. 

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