THE TELEGRAPH 325 



operators are needed at each end, six to send and six to re- 

 ceive; one line may thus employ twenty-four operators. 

 For this there must be a separate key for each sender and a 

 separate sounder for each receiver. 



High speed telegraphy. When it is desired to transmit 

 long messages for newspapers, the hand method of sending 

 would be too slow. For this purpose machines are used 

 which send messages with great rapidity. Several systems 

 are able to send 400 words per minute. In one system words 

 have been sent at rates varying from 1000 to 3000 words per 

 minute. This is much more rapid than even the telephone. 



The words of the message are first translated into the 

 Morse alphabet, and perforations are made by a machine 

 on a strip of paper to correspond to the dots and dashes of 

 the alphabet. This is done by a machine much like a type- 

 writer, each key of which makes the holes that correspond 

 to the dots and dashes for that letter. This strip of paper 

 is run through telegraphic instruments so arranged that the 

 signals are transmitted to the other end. 



Various means are used to receive these messages. One 

 of the most common is an electrochemical receiver. Paper 

 is covered with certain chemicals which are decomposed by 

 the electric current and leave markings on the paper. One 

 combination used is starch and potassium iodid. When 

 this salt is decomposed, the iodin is set free, and when it 

 comes in contact with the starch it produces a blue color. 

 Machines are now in use which reproduce the message in 

 typewritten form, ready for instant delivery and use. 

 This machine has made a record of 100 words a minute. 



Facsimile telegraphy. Devices are now used which make 

 it possible to transmit accurate copies of charts, diagrams, 

 pictures, and signatures over a telegraph line. This is called 

 facsimile telegraphy. If a person takes a pen in a telegraph 

 office and writes a message, it is possible to reproduce it so 

 accurately at the other end, that the handwriting may be 



