Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Telecommunication is the transmission of messages, over significant distances, for the purpose of communication. In earlier times, telecommunications involved the use of visual signals, such as smoke, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for example. In the modern age of electricity and electronics, telecommunications has typically involved the use of electric means such as the telegraph, the telephone, and the teletype, the use of microwave communications, the use of fiber optics and their associated electronics, and/or the use of the Internet. The first breakthrough into modern electrical telecommunications came with the development of the telegraph during the 1830s and 1840s. The use of these electrical means of communications exploded into use on all of the continents of the world during the 19th century, and these also connected the continents via cables on the floors of the ocean. These three systems of communications all required the use of conducting metal wires.