Radio did not emerge as a full-blown mass medium until the 1920s, though the technology that made radio possible had been evolving for years. The telegraph—the precursor of radio technology—was invented in the 1840s. American inventor Samuel Morse developed the first practical system, sending electrical impulses from a transmitter through a cable to a reception point. Using what became known as Morse code—a series of dots and dashes that stood for letters in the alphabet—telegraph operators transmitted news and messages simply by interrupting the electrical current along a wire cable. By 1844, Morse had set up the first telegraph line between Washington, D.C., and Baltimore. By 1861, telegraph lines ran coast to coast. By 1866, the first transatlantic cable, capable of transmitting about six words a minute, ran between Newfoundland and Ireland along the ocean floor.

Although it was a revolutionary technology, the telegraph had its limitations. For instance, while it dispatched complicated language codes, it was unable to transmit the human voice. Moreover, ships at sea still had no contact with the rest of the world. As a result, navies could not find out that wars had ceased on land and often continued fighting for months. Commercial shipping interests also lacked an efficient way to coordinate and relay information from land and between ships. What was needed was a telegraph without the wires.

Popular Radio and the Origins of Broadcasting