222 APPLIED SCIENCE 



causing his own sounder and the one at the other end to click. 

 Because of the great resistance to the current, the electricity 

 by the time it reaches the end of the line is so feeble that 

 it is necessary to place in the local circuit a battery and a 

 second electromagnet, called a sounder. On the main line 

 there is another electromagnet, called a relay. This has a 

 greater resistance, due to its fine wire, than the sounder, 

 which has a small resistance. 



When the telegraph operator at one end of the line presses 

 on the key so as to close the circuit, the magnets at the other 

 end of the line become magnetic, the end of the lever is 

 attracted and drawn down by the magnets, the other. end 

 is pushed up and the steel point presses against the paper 

 and dents a line in it. This line is made so long as the key 

 is kept pressed down in the sending office. 



As soon, however, as the sending operator takes his fingers 

 from the key, the circuit is broken. The magnets in the 

 register at the receiving station then lose their power on the 

 lever, the end drops down, and a blank space is left on 

 the paper. When the operator in the sending station taps 

 on the key so as to close the circuit only for an instant, a dot 

 or very short line is made on the paper in the receiving station 

 as shown on the table below. By pressing on the key a little 

 longer time, or not at all, the operator can make dots, lines, 

 or blank spaces on the paper in the receiving station. By 

 putting together these lines and dots in different ways all 

 the letters of the alphabet may be made, so that any kind 

 of a message may be sent. 



The alphabetical application of the dot-and-dash code 

 invented by Morse was made in 1837 by Alfred Vail, though 

 it is universally known as the Morse alphabet. This alpha- 

 bet, which is used in the United States and Canada, and in 



