Irk vs Sow

Irk

name
  • A river in Greater Manchester, England, which joins the River Irwell in Manchester city centre. 

Sow

name
  • A river in Staffordshire, England, which joins the River Trent. 

  • A surname. 

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