1A signalling device by which sunlight is reflected in flashes from a movable mirror.
1.1 A message sent by heliograph; a heliogram.
2A telescopic apparatus for photographing the sun.
3historical A type of early photographic engraving made using a sensitized silver plate and an asphalt or bitumen varnish.
1Send (a message) by heliograph.
2historical Take a heliographic photograph of.