326 SCIENCE OF HOME AND COMMUNITY 



recognized. Thus it is possible for a person to telegraph 

 his signature to a check or other paper requiring a personal 

 signature. This is called the writing telegraph or telauto- 

 graph. 



By means of the printing telegraph, messages may be sent 

 so that they are received printed on a strip of paper. The 

 stock ticker, which is one form of this, is very widely used 

 among brokers. 



DEMONSTRATION 24 



Purpose. To show how a set of telegraph instruments work. 



Apparatus. Sounder, sender, relay, cells. 



Directions. Connect the parts of the telegraph instruments 

 including the relay, as shown in figure 132. Study each part 

 carefully to see how it works. Make a drawing showing the 

 connections. Try sending some of the letters of the Morse 

 alphabet. 



Wireless telegraphy. Use. If to-day a ship at sea is in 

 danger of sinking on account of some accident, the operator 

 of the -wireless telegraph sends out the S. O. S. signal, the 

 call for help. This travels in every direction for many miles, 

 and some ship is almost certain to receive the message and 

 will hasten then to the aid of the crippled ship. Thus many 

 lives have been saved, and the sea is now robbed of many of 

 its terrors by the wireless telegraph. 



Nearly all the ocean liners .are provided with wireless 

 telegraph instruments, so that people on board can keep in 

 communication with their friends on shore, and the business 

 man can still direct his affairs. Daily newspapers are pub- 

 lished on some of the larger boats, the news having been 

 received by wireless. 



History of wireless telegraph. The chief credit for the 

 development of wireless telegraphy is due to Marconi, who 

 was the first to develop a practical instrument. As is true 

 of all inventions, this was made possible only through the 



