conduit vs vacuum tube

conduit

noun
  • A duct or tube into which electrical cables may be pulled; a type of raceway. 

  • A pipe or channel for conveying water, etc. 

  • A means by which something is transmitted. 

  • An investment vehicle that issues short-term commercial paper to finance long-term off-balance sheet bank assets. 

vacuum tube

noun
  • A type of electron tube that controls electron current through vacuum between electrodes within a sealed container, usually of glass or metal and often designed to be easily installed in and removed from the equipment in which it is used. 

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