ELECTRICAL APPLIANCES AND MACHINES 263 



sent the famous message, "What hath God wrought." 

 This was the first message sent over the wire from Wash- 

 ington to Baltimore. From that time telegraph systems 

 increased rapidly, until now a message can be sent around 

 the world in a few minutes. 



When the key, K (see illustration), in Pittsburgh is 

 closed the current flows over the line to Chicago. There 

 it passes through the electromagnet, M, and thence back 

 to Pittsburgh through the ground. The armature, A, 



SHOWING THE PRINCIPLE OF THE TELEGRAPH 



is held down by the magnet, M, as long as the key, K, 

 is kept closed. As soon as the current is broken by 

 releasing the key, K, the magnet, M, is demagnetized 

 and the armature, A, is pulled up by the spring, S. By 

 means of clockwork the tape, T, is drawn along at a 

 uniform rate beneath the pencil or pen held by the arma- 

 ture, A. A very short time of closing of the key, K, 

 produces a dot upon the tape; if the key is closed for a 

 longer time a dash will be produced. By this simple 

 method a message could be sent to Chicago without the 

 operator at Chicago being present at the time. 



Many- improvements have been made on the Morse 

 system so that now operators can call one another and 

 can take a message by sound, thus avoiding the necessity 

 of having the writing apparatus. A very short interval 

 of time between two clicks of the sounder is interpreted 

 as a dot, a longer interval is interpreted as a dash. 



