Harrow vs Slough

Harrow

name
  • A town in northwestern Greater London, England. 

  • A London borough of Greater London, England. 

  • A prestigious public school for boys in the town of Harrow. 

  • A surname originating as an occupation for a harrower. 

Slough

name
  • A town in east Berkshire, England (formerly Buckinghamshire), close to Heathrow Airport. 

  • A borough and unitary authority (Slough Borough Council) in Berkshire. 

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