Morse code most common letter in English, the letter "E", has the shortest code: a single dot. Because the Morse code elements are specified by proportion rather than specific time durations, the code is usually transmitted at the highest rate that the receiver is capable of decoding. The Morse code transmission rate ("speed") is specified in "groups per minute", commonly referred to as "words per minute". Morse code is usually transmitted by on-off keying of an information carrying medium such as electric current, radio waves, visible light or sound waves. The current or wave is present during time period of the dot
American Morse code US needing to be proficient in both codes since messages on transatlantic cables were in the international code, and incoming messages needed to be recoded and sent on in American Morse. An attempt in 1854 to make International Morse the standard within the US was rejected by the telegraph companies. Overhead wires, used for most land routes in the US, have nowhere near as big a problem with dispersion as undersea or underground cables and the companies had no wish to retrain their staff. In the late 1890s, radio communication—initially known as "wireless telegraphy"—was invented, and used Morse Code transmissions.