In palm recognition a 3-dimensional image of the hand is collected and compared to the stored sample. Palm recognition devices are cumbersome artefacts (unlike fingerprint and iris recognition devices) but can absorb perform a great amount of identification acts in a short time. They are therefore preferably installed in situations where a large number of people is identified, as in airports.
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The Roman smoke signals network consisted of towers within visible range of each other and had a total length of about 4500 kilometers. It was used for military signaling.
For a similar telegraph network in ancient Greece see