Other biometric technologies not specified here include ear recognition, signature dynamics, key stroke dynamics, vein pattern recognition, retinal scan, body odour recognition, and DNA recognition. These are technologies which are either in early stages of development or used in highly specialised and limited contexts.
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Claude Chappe built a fixed optical network between Paris and Lille. Covering a distance of about 240kms, it consisted of fifteen towers with semaphores.
Because this communication system was destined to practical military use, the transmitted messages were encoded. The messages were kept such secretly, even those who transmit them from tower to tower did not capture their meaning, they just transmitted codes they did not understand. Depending on weather conditions, messages could be sent at a speed of 2880 kms/hr at best.
Forerunners of Chappe's optical network are the
For more information on early communication networks see