You searched for: “heliogram”
heliogram (s) (noun), heliograms (pl)
A communication transmitted on an apparatus for sending telegraphic messages by using a mirror to turn the sun's rays on and off or a signal by means of a mirror and while using the sun's rays.
This entry is located in the following units: gram-, -gram-, -gram, -grammatic, -grammatical, -grammatically, -gramme, -grammic + (page 10) helio-, heli- (page 2)