effluvium vs natural gas

effluvium

noun
  • A gaseous or vaporous emission, especially a foul-smelling one. 

  • A condition causing the shedding of hair. 

natural gas

noun
  • A mixture of gaseous hydrocarbons associated with petroleum deposits; mostly methane with smaller amounts of ethane, propane and butane; principally used as a fuel. 

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