268 



COMMUNICATION 



The invention of the telegraph. The use of elec- 

 tricity for communication had been thought of by 

 Franklin and later had been worked out in the labora- 

 tory by Joseph Henry in Albany, N.Y., about 1831. 

 In 1832, while returning to America by ship, Samuel 

 F. B. Morse, an artist and teacher, began to think of 

 the possibilities of using the electromagnet in com- 

 munication. Giving up a career in art, he devoted him- 

 self and all of a small fortune to perfecting a tele- 



E 

 I 

 M 



Q 

 U 

 Y 



B 

 F 



J 

 N 

 R 

 V 

 Z 



G 

 K 

 O 



S 



w 



1 



D 

 II 

 L 



P 

 T 

 X 



2 



FIG. 430. AMERICAN MORSE CODE 



graph. By 1843, working with Alfred Vail, Morse had 

 completed his invention and was ready to give it to 

 the world. He had worked out a code consisting of 

 "dot" and "dash" combinations to represent letters of 

 the alphabet which is still used in modern telegraphy. 



Morse secured a grant of $30,000 from the United 

 States in 1843 and at once set about the construction 

 of a telegraph line between Baltimore and Washing- 

 ton. On May 24, 1844, Morse sent these memorable 

 words, "What hath God wrought," from Washington 

 to Vail, seated forty miles away in Baltimore. From 

 this small beginning the telegraph has developed into 

 one of our most important devices for communica- 

 tion. 



What are the parts of a simple telegraph and how 

 are these parts connected into a telegraph circuit? 

 In one of the experiments which was performed in the 

 unit on electricity you worked with electromagnets. 

 How did the electromagnet act when electric cur- 

 rent was flowing through its coil ? What happened 

 when the current was turned off? The telegraph is 

 made of two devices, a key or sender and a sounder or 

 receiver. These are shown connected with a battery by 

 a wire in* Figure 431. The key is used to close and 

 open the electric circuit much as a switch. When the 



key is pressed down the circuit is completed and 

 current flows from the battery through the key and 

 sounder and back to the battery. When the key is 

 released it is pushed open by springs, thus breaking 

 the circuit and stopping the flow of current from the 



DRV 

 CELL 



FIG. 431. TELEGRAPH SOUNDER AND RECEIVER 



battery. The sounder is made of an electromagnet 

 over which is mounted an iron bar. The bar is pulled 

 down by the magnet when current flows through its 

 coils and is drawn back by a spring when the current 

 is not flowing. As the bar is drawn down it makes a 



\ 



FIG. 432. ONE-WAY TELEGRAPH BETWEEN ROOMS 



