They found that telegraphic messages are transmitted by the use of three independent characters: short signals, or dots; long signals, or dashes; and dividing intervals or spaces between adjacent signals. Thus, a dot followed by a dash represents the letter a; a dash followed by three dots represents the letter b, while two dots, space, dot, represents the letter c, and so through the alphabet, which, according to the Morse code, is written like this: a, .-; b, -...; c, .. .; d, -..; e, .; and so on. Longer spaces or pauses divide the words, and longer dashes are also used in representing some of the letters. The dots and dashes are made by means of a key which opens and closes the electric circuit, and causes the sounders of all the other instruments connected with the wire to vibrate responsively. When an operator desires to send the letter a, he depresses his key for a short interval, then releases it, and, after an interval equally brief, depresses it again, holding it down three times as long before releasing it. All the other sounders repeat this dot and dash, and the listening operators recognize the letter a. Every word must be spelled out in this manner, letter by letter. As may well be believed, the boys found the sending and receiving of even the shortest words difficult and painful enough at first, but in a surprisingly short time certain combinations of sounds began to stand out, as it were, among their surroundings. The two combinations which first became familiar were - .... . and .- -. -.., representing respectively "the" and "and." Following this, came the curious combination of sounds, ..--.., which represents the period, one of the most difficult the learner has to master. Other combinations followed, until most of the shorter words began to assume the same individuality when heard over the wire that they have when seen by the eye. It was no longer necessary to listen to them letter by letter; the ear grasped them as a whole, just as the eye grasps the written word without separating it into the letters which compose it.