Telegraphy is the long-distance transmission of textual (as opposed to verbal or audio) messages without the physical exchange of an object bearing the message. Thus semaphore is a method of telegraphy whereas pigeon post is not.
Telegraphy requires that the method used for encoding the message be known to both sender and receiver. Such methods are designed according to the limits of the signalling medium used. The use of smoke signals, beacons, reflected light signals, and flag semaphore signals are early examples. In the 19th century, the harnessing of electricity brought about the means to transmit signals via electrical telegraph.
The advent of radio in the early 1900s brought about radiotelegraphy and other forms of wireless telegraphy. In the Internet age, telegraphic means developed greatly in sophistication and ease of use, with natural language interfaces that hide the underlying code, allowing such technologies as electronic mail and instant messaging. Telegraphy systems operated in Europe from as early as 1792 in the form of semaphore lines, or optical telegraphs, that sent messages to a distant observer through line-of-sight signals. In 1837, American artist-turned-inventor Samuel F. B. Morse conducted the first successful experiment with an electrical recording telegraph.
The first UK public telegraph carrier, the Electric Telegraph Company, originated in 1846.