Tuesday, July 10, 2018

Telecommunication in ancient Greece

The Greek historian Polybius (c. 200 – c. 118 BC) documented two methods for communication at a distance -- telecommunication.

The first was an analog hydraulic system. The terminals consisted of identical vessels filled with water. The sender signaled the receiver with a torch when he was ready to transmit and they both let water out of their vessels until the end of transmission torch was raised. If the amount of water drained from both vessels was the same, the height of the water in the receiver designated the message.

This method was imprecise and could only transmit one of a number of pre-defined messages. The second, digital method could transmit any written message. It used a 5-bit representation of characters to send messages using torches. Messages were transmitted one character at a time by raising torches in two of five positions.

The operators had identical tablets showing the letters and the torch positions (1-5) designated the column and row of the letter being sent. If this tablet were used:

the message 22, 51, 13, 13, 45 would spell out ΗΕΛΛΩ.

Note that messages could be encrypted by changing the tablets.

(If you find this interesting, check out Claude Chappe's French telecommunication system).