thermionic valve vs torch

thermionic valve

noun
  • An electronic device incorporating electrons from a glowing cathode inside an evacuated glass tube, functioning as a switch, amplifier etc. 

torch

noun
  • A portable light source powered by electricity; a flashlight. 

  • An arsonist. 

  • A stick with a flame on one end, used chiefly as a light source; a similarly shaped implement with a replaceable supply of flammable material. 

  • A blowtorch or oxy-gas torch. 

  • A torch drive ("a spacecraft engine which produces thrust by nuclear fusion"). 

verb
  • To set fire to, especially by use of a torch (flaming stick). 

  • To travel in a spacecraft propelled by a torch drive ("a spacecraft engine which produces thrust by nuclear fusion"). 

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