 Telegraphy, telegraphy is the long-distance transmission of textual or symbolic as opposed to verbal or audio messages without the physical exchange of an object bearing the message. Thus semaphore is the 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. Many methods are designed according to the limits of the signaling 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 led to the invention of electrical telegraphy. The advent of radio in the early 20th century brought about radio telegraphy 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.