heliograph vs radar

heliograph

noun
  • An instrument for measuring the intensity of sunlight. 

  • A heliogram. 

  • A device for photographing the sun. 

  • An apparatus for signalling by means of a moveable mirror which reflects flashes of sunlight. 

verb
  • To send a message by heliograph. 

  • To send a heliograph. 

radar

noun
  • A method of detecting distant objects and determining their position, velocity, or other characteristics by analysis of sent radio waves (usually microwaves) reflected from their surfaces 

  • A type of system using such a method, differentiated by platform, configuration, frequency, power, and other technical attributes. 

  • An installation of such a system or of the transmitting and receiving apparatus. 

  • A superior ability to detect something. 

verb
  • To scan with radar, or as if with radar. 

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