The German professor Carl Friedrich Gauss of the University of Göttingen developed and used a predecessor of the heliograph (the heliotrope) in 1821.^[1][9] His device directed a controlled beam of sunlight to a distant station to be used as a marker for geodetic survey work, and was suggested as a means of telegraphic communications.^[10] This is the first reliably documented heliographic device,^[11] despite much speculation about possible ancient incidents of sun-flash signalling, and the documented existence of other forms of ancient optical telegraphy.