A character code invented by Samuel Morse that is represented by the duration of a single tone. Written as dots, dashes and spaces, the first Morse code message was sent in 1844 over a newly constructed telegraph line between Baltimore and Washington. It was also used in World War II for signaling with flashes of light. A variation of Morse's original code was made by Friedrich Gerke in 1848, which evolved into the International Morse Code that is still in use.

The coding system was based on the frequency of letters used in the English language, E and T being the most frequent, hence one dot, one dash. The written system is dot and dash, but it is pronounced "dit" and "dah." Timing within the code is one dit between each dit and dah, three dits between letters and seven dits between words. See telegraph.

  International Morse Code

  A   .-       U   ..-    
  B   -...     V   ...-   
  C   -.-.     W   .--    
  D   -..      X   -..-   
  E   .        Y   -.--   
               Z   --..   
  F   ..-.
  G   --.      0   -----  
  H   ....     1   .----  
  I   ..       2   ..---  
  J   .---     3   ...--  
               4   ....-  
  K   -.-      5   .....  
  L   .-..     6   -....  
  M   --       7   --...  
  N   -.       8   ---..  
  O   ---      9   ----.  

  P   .--.     Period      .-.-.-
  Q   --.-     Comma       --..--
  R   .-.      ? Mark      ..--..
  S   ...      Hyphen      -....-
  T   -        Apostrophe  .----.
               Colon       ---...
  U   ..-      Quotation   .-..-.
  V   ...-     Slash       -..-.
  W   .--      @ sign      .--.-.
  X   -..-
  Y   -.--
  Z   --..