1. An apparatus that uses a mirror or mirrors to reflect sunlight and transmit messages in Morse code over long distances.
Usage: historical military communication device; also called sun telegraph
2. A photograph made by the action of sunlight on a chemically treated surface.
Usage: archaic; early photography term

1. To send a message using a heliograph; to communicate by heliograph.
Usage: historical

Examples

• The military unit used a heliograph to send urgent messages across the desert.
• Before radio communication, soldiers relied on heliographs to transmit orders over vast distances.
• The heliograph operator positioned the mirror to catch the sun's rays at the correct angle.
• Early photographers experimented with heliographs to create images without a camera lens.
• They heliographed the coordinates to the distant battalion using Morse code.