Heliograph

Technology

The heliograph is an advanced technology (though not a work of artifice) in use by the Realm and a handful of larger Threshold states, which conveys signals by way of flashes of sunlight reflected by huge mirrors mounted on tall towers. The flashes are produced by interrupting the beam with a shutter system.

Heliograph signals can reach out over a hundred miles in good weather, and a network can pass a missive from one side of the Blessed Isle to another in just two or three days in sunny weather. The beams are narrow, meaning the signals are undetectable outside a relatively narrow band, allowing two towers to communicate without broadcasting their signals to others. However, the system cannot be secured…. An observer within the line of the beam can record the flashes undetected by transmitter or receiver.

Some heliograph towers are equipped with mirror systems and lanterns to allow flashes to be directed at night, though the difficulty and fuel costs of this are extraordinary and so it is rarely used, the Realm employing it only for emergency Thousand Scales communiqués.

Cryptography

The system of flashes and pauses used by operators is not standardized across Creation... each operator has a different heliograph language, which mustr be understood by the receiver for communication to take place. The Realm uses a complex system of coded language, created and updated by the cryptographers of the Imperial Post. The code changes by month and involves complex formulas, with a codebreaker having first to decipher the words and syntax being spelled out by the flashes and THEN discern the meaning behind those words.

While one codebook might be stolen, a full set of all fifteen is unlikely to go missing, as each station keeps books in a steel vault and Post officials are trained to destroy their codebooks if a Post station seems likely to fall to hostile forces.

The Imperial Legions also maintain codebooks for Legion communications, as do various ministries and Great Houses. Messages they hand to the Imperial Post for sending are thus already coded before ever reaching the eyes of postal officials, decoded by the recipient after the Post delivers it.

Theology

Each heliograph system, when it is assembled, is blessed with prayers of thanks to the Unconquered Sun (carried out by Immaculate monks in the Realm) for His service in providing light that shines across Creation. Gods of communication and the heliograph technology itself are supportive of its use, gods of messengers and paper letters tend to oppose it, but the issue is largely ignored in Heaven where access to instant long-range communication is easy.