Telecommunications and Space Exploration

Abstract

Technically speaking, signals such as the train’s whistle, the blinking of a car’s beams,$\ldots$ are quantities, varying in time, to which an informative content is assigned. The signals of smoke by day and fire by night, used by American Indians in early colonial times, are just another example, common to ancient civilizations from China to Greece. In the play Agamemnon by the Greek dramatist Aeschylus, quantitative information can be found: Nine relay points on natural prominences covered a distance of 800 km, by means of beacons of fires, to bring to Queen Clytemnestra in Argos the news of the imminent homecoming—from the Trojan war—of her victorious husband and to prompt her desire for vengeance. It was more than a thousand years before Christ. These may be regarded as early forms of telegraphy, which means “to write far” from the Greek. In telegraphy a message, consisting of a set of words, is transmitted by ascribing to each letter a certain coded signal.