158 future's 



upon the current transmitted through it. An 

 ordinary land-line that is strung on poles that 

 are high up from the ground has this effect re- 

 duced to a minimum, but the greater the num- 

 ber of wires clustered together on the same 

 poles the more difficult it becomes to send 

 rapid signals through any one of them. 



The instrument used for receiving cable 

 messages was devised by Sir William Thomp- 

 son, now Lord Kelvin. One form consists of 

 a very short and delicate galvanometer-needle 

 carrying a tiny mirror. This mirror is so re- 

 lated to a beam of light thrown upon it that it 

 reflects it upon a graduated screen at some dis- 

 tance away, so that its motions are magnified 

 many hundred times as it appears upon the 

 screen. An operator sits in a dark room with 

 his eye on the screen and his hand upon the 

 key of an ordinary Morse instrument. He 

 reads the signal at sight, and with his key 

 transmits it to a sounder, which may be in 

 another room, where it is read and copied by 

 another operator. Another form of receiving- 

 instrument carries, instead of the mirror, a 

 delicate capillary glass tube that feeds ink 

 from a reservoir, and by this means the move- 

 ments of the needle are recorded on a moving 

 strip of paper. The symbols (representing 

 letters) are formed by combinations of zigzag 

 lines, This instrument is the syphon-recorder, 



