A telegraph is a machine that is used for transmitting messages in the form of electrical impulses, which can be converted into data. A message sent this way is called a telegram or cablegram, while someone who operates a machine is known as a telegrapher. Telegraphy was a major mode of communication from the middle of the 1800s until well into the 1900s, before ultimately being supplanted by inventions like the telephone and the Internet.
The earliest version of the telegraph was developed in the late 1700s, primarily as a thought exercise. This early draft only existed on paper, but it laid the groundwork for various incarnations of the device that appeared in the early 1800s. With the development of the electromagnet, Samuel Morse and Alfred Vail were able to develop and patent a reliable electric system in 1837.
Morse is often credited with being the inventor of the telegraph, but this is not the case. Many other inventors had patented various versions of the machine before Morse, and history strongly suggests that Alfred Vail was the scientific brains of the operation. Morse popularized the device, however, and developed a workable, easily learned alphabet that could be transmitted using it.
Originally, the machines had to be connected through a series of wires in order to exchange messages. The operator would key a message in the Morse alphabet, and the receiving machine on the other side would register the message in the form of clicks made by one bar that struck another. By listening to the pattern of clicks, the receiving operator could hear the message and transcribe it before passing it on to the recipient.
In the late 1800s, wireless telegraphy began to emerge, and messages were transmitted over the radio waves. This marked a drastic change in the system, allowing people to rapidly transmit messages in areas without cables, and enabling things like ship-to-ship communication. Wireless telegraphy, or radiotelegraphy, also laid the groundwork for later methods of communication.
The telegraph is largely obsolete now. One famous company, Western Union, sent its last telegram in 2006, and many other companies have stopped offering telegram services because consumer demand has fallen radically. Telegrams are generally regarded as interesting curiosities, as is the peculiar language used in them. Because transmitting the signal is painstaking, operators developed their own shorthand to make transmission more rapid.