An Experimental Apparatus.

In 1920 radio was still in the experimental stage. Guglielmo Marconi invented wireless telegraphy in 1899. The wireless telegraph sent a series of dot and dash signals through space, using the same code invented in the 1840s by Samuel Morse. In 1906 an actual voice communication was transmitted, and wireless telephony was invented. Both forms of communication were commonly called "wireless," but in 1912 the U.S. Navy ordered that the terms radiotelegraphy and radiotelephony be employed instead. The American public rapidly accepted the change, but by 1920 the simple term radio had become the American name for the still experimental invention. The British, however, continued using the term wireless for most of the twentieth century.

Vacuum Tubes.

The earliest radios were crystal sets, difficult to tune and operate. During World War I, however, developments in vacuum tubes, devices similar to light bulbs and the ancestors of...