add. ·vt to photograph by sunlight.
2. heliograph ·noun a picture taken by heliography; a photograph.
3. heliograph ·noun an instrument for taking photographs of the sun.
4. heliograph ·add. ·vt to telegraph, or signal, with a heliograph.
5. heliograph ·noun an apparatus for telegraphing by means of the sun's rays. ·see heliotrope, 3.