Source : Webster's Revised Unabridged Dictionary (1913)

Heliograph \He"li*o*graph\, v. t.
   1. To telegraph, or signal, with a heliograph.

   2. To photograph by sunlight.

Heliograph \He"li*o*graph\, n. [Helio- + -graph.]ets>
   1. A picture taken by heliography; a photograph.

   2. An instrument for taking photographs of the sun.

   3. An apparatus for telegraphing by means of the sun's rays.
      See {Heliotrope}, 3.

Source : WordNet®

heliograph
     n : an apparatus for sending telegraphic messages by using a
         mirror to turn the sun's rays off and on
     v : signal by means of a mirror and the using the sun's rays