TELEGRAPH 



5735 



TELEGRAPH 



is part of a letter combination is equal to two 

 dots. 



Sending Four Messages at One Time over One 

 Wire. One of the marvelous achievements in 

 telegraphy is that of sending a number of mes- 

 sages at one time over one wire. One electric 

 current can be made to convey four messages 



A B C D E F 



Call 



Finish 



THE CONTINENTAL CODE 

 Dots and dashes are employed to form the let- 

 ters. Spaces are used only to indicate the end of 

 one 'letter and the beginning of the next. 



at one time, two going in one direction and 

 two in the opposite direction, and the mes- 

 sages do not interfere with each other. To 

 send two messages at one time in opposite di- 

 rections the instruments must be so arranged 

 that the sounder is in the circuit but is not 

 affected by the sending instrument at the same 

 station. 



A telegraph system by means of which two 

 messages can be sent at one time is called a 

 duplex system. In the duplex system the mak- 

 ing and breaking of the circuit operates the 

 sounder, regardless of the direction in which 

 the current flows. In another system of duplex 

 telegraphy it is by changes in the direction of 

 the current that the signal is transmitted. When 

 these two systems are combined in one wire a 

 single current will transmit four messages at 

 one time, developing a quadruplex, or fourfold, 

 system. We may think of the fourfold system 

 as working in the following manner: 



There are two receivers and two sending in- 

 struments at each end of the line, all connected 

 to one line wire. They are so arranged that 

 the outgoing messages from station 1 do not 

 affect the receiving instruments at station 1. 



Messages sent from station 1 affect only the 

 sounders at station 2. A constant current is 

 flowing in the line, but the receiving instru- 

 ments are so arranged that none of them is 

 moved by this current unless a change is made 

 either in the direction or the strength of the 

 current. If the direction of the current is 

 changed at station 1, one sounder at station 2 

 responds with a click, but the other sounder at 

 station 2 is not affected. If the strength of the 

 current is changed at station 1 the second 

 sounder at station 2 responds. Thus two sig- 

 nals are sent at the same time from station 1 

 to station 2. In the same way and at the same 

 time two signals may be sent from station 2 to 

 station 1. 



Every telegraph line of importance is at least 

 arranged for duplex telegraphy and many are 

 quadruplexed. 



Use of the Dynamo. For long-distance teleg- 

 raphy dynamos are used to supply current to 

 the line. They occupy less space and are more 

 economical than batteries. A generating plant 

 sufficient to operate a thousand lines may be 

 installed in a small room. The lines may vary 

 in length from fifty to 500 miles. 



Batteries. When batteries are used for long- 

 distance work, storage' cells are always used. 

 The gravity, or Daniell, cell is used for local 

 circuits only, and even for local circuits stor- 

 age cells are frequently used. 



Telegraphing without Wires. See WIRELESS 

 TELEGRAPH. 



Submarine Telegraph. See CABLE, SUBMA- 

 RINE. 



Printing Telegraph. The printing telegraph 

 delivers the message in printed form on a tape 

 or in typewritten pages. The operator need 

 not know the Morse code. He operates a type- 

 writer keyboard as if he were typewriting a let- 

 ter. In some forms of printing telegraph a spe- 

 cial form of typewriter receives the message. 

 Each key of the receiving typewriter is con- 

 trolled by a small electromagnet. Each of 

 these electromagnets has its own combination 

 of electric impulses to which it responds and 

 which is sent over the line when the corre- 

 sponding key is depressed at the sending end. 

 Four messages, two in each direction, may be 

 sent at one time over the line by the printing 

 telegraph. The stock ticker is a form of print- 

 ing telegraph in which the messages are printed 

 on a tape. It is used in telegraphing market 

 quotations. 



High-Speed Telegraphy. An automatic de- 

 vice for operating the electrical contacts makes 



