Zeppelin vs weather balloon

Zeppelin

noun
  • A type of large dirigible rigid airship of the early 20th century, built by the German Luftschiffbau Zeppelin and designed to carry passengers or bombs. 

  • A rigid airship dirigible, not restricted to Germany nor the early 20th century. 

name
  • A German manufacturing company, famed for building the zeppelin airships. 

weather balloon

noun
  • a balloon that carries meteorological instruments aloft in order to measure, record and return data concerning atmospheric pressure, temperature and humidity 

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