linkman vs travelling salesman

linkman

noun
  • A man who acts as a link or connection. 

  • A presenter who provides the connecting verbiage between a number of separate items in a broadcast. 

  • A player who uses speed and dexterity to keep an attacking team's downfield progress fluid. 

  • An adult linkboy; one bearing a torch or light. 

travelling salesman

noun
  • A man who travels, often within a certain territory, soliciting orders or selling goods. 

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