Answer: heliograph

AnswerCrossword Clue
heliographan apparatus for signalling by means of a movable mirror which reflects flashes of sunshine / to signal by heliograph
heliographinstrument for photographing the sun, consisting of a camera and a specially adapted telescope
heliographdevice for signaling by means of a movable mirror that reflects beams of light, esp. sunlight, to a distance
heliographinstrument for recording the duration and intensity of sunshine
heliographto communicate by heliograph