Firth vs Tarn

Firth

name
  • A village in Nebraska. 

  • A city and town in Idaho. 

  • A surname. 

  • A small village in north-east Mainland, Shetland Islands council area, Scotland (OS grid ref HU4473). 

Tarn

name
  • A river in southwestern France. 

  • A department of Occitanie, France; previously in Midi-Pyrénées (INSEE code 81). 

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