City of Phoenix
Lightning Line System
These are magical apparatus that tap into the Astral Plane and use Astral Filaments to transmit messages. Messages can be sent from one station to another, where they are transcribed to written form and then delivered to the recipient by hand. The messages are sent in a simple code that transmits well over the Astral Filaments.
Each station has an alchemical jar, which contains a tiny lightning elemental. The base of the jar has an Astral Filament that connects it to the Astral Plane, when the jar is tapped with a gold tuning hammer it causes the elemental to pulse in a certain way. This pulse then travels along the Astral Filament and is received at the destination station. Which station or stations receive the message is determined by rotating the alchemical jar on a compass like platform. All stations along that compass line will receive the message. Messages are usually sent with the intended destination as the first word, so that any other stations that might receive the message know it is not intended for them.
Messages sent in this manner can usually reach the recipient in a single day. Only relatively short messages can be sent in this manner, since to do otherwise would tie up the network of message stations unduly.
The contact of the gold hammer is what causes the elemental inside the jar to pulse, so the longer the hammer is in contact with the jar the longer the pulse.
All major cities in Mistabar have a Lightning Line Office, and many larger communities. They become more rare in rural areas, but the government has established a few in frontier and border communities to serve as an early warning in the case of disaster or border incursion by a hostile force.
This is obviously a form of telegraph system for purposes of mechanics