1) An instrument for photographing the Sun, consisting of a camera and a
specially adapted telescope.
2) A simple device using a mirror to reflect sunlight to a distant observer. By moving the
mirror, flashes of light can be used to send coded messages. The heliograph was a
highly effective instrument for instantaneous optical communication over 80km or
more in the 19th century.
3) Meteo.: An instrument which records the duration of sunshine and gives
a quantitative measure of the amount of sunshine.
→ helio-; + → -graph.