74 THE POPULAR SCIENCE MONTHLY. 



In every form of electric telegraph the signals are given by an in- 

 termittent now of electricity. In the Morse system a " key " is used 

 which, in its normal position, " breaks " the circuit, but when depressed 

 by the linger of the operator allows the electricity to pass through it 

 on its mission. Arrived at the distant station, it is converted, by 

 means of an electro-magnet, into mechanical motion, which is utilized 

 either to produce indentations in a moving slip of paper by means of 

 a style, or, more commonly, to give a series of taps, which the operator 

 understands, by an instrument called a " sounder." 



In the automatic system the means employed are altogether dif- 

 ferent. The message is, first of all, prepared by punching holes in a 

 narrow ribbon of paper. These perforations are so grouped as to 

 represent the dots and dashes of the telegraphic alphabet, and by 

 the punching-machine, which is very complicated, all that are required 

 to form a letter are punched at one stroke. In comparing the two sys- 

 tems this must not be lost sight of, as the time taken in punching 

 must, of course, be added to the time of transmission. The machine, 

 however, does its work more quickly than the Morse operator with 

 his key, and, the time occupied in transmitting being so vastly less, 

 the "automatic" may claim to have rendered old-fashioned telegra- 

 phy comparatively slow. 



After the perforated slip of paper has been prepared, it is taken to 

 the operator's table, where it is made to move forward rapidly be- 

 tween a metallic drum and a needle carrying two small steel wheels 

 which rest upon it. Drum and wheels form part of the circuit, which 

 is broken by the non-conducting paper interposed and closed when 

 the holes permit of the wheels and the metallic cylinder beneath 

 coming into contact. At -the receiving-station a very similar arrange- 

 ment does duty as a register. The paper slip is there saturated with 

 a certain chemical solution which renders its whole substance a good 

 conductor, and, instead of the wheels, there is an iron style or " pen." 

 When electricity arrives over the line, it decomposes the moisture of 

 the paper into oxygen and hydrogen, and oxidizes or rusts the pen. 



OO O O O op 



Fig. 3. 



A little of this oxide is rubbed off by the quickly-moving paper, and 

 enters into combination with the chemical still contained in it, pro- 

 ducing a stain in the form of a dot or dash which corresponds with 

 the holes punched in the paper at the sending-station. Where three 

 holes come together, both wheels form a contact, and a dash is pro- 

 duced, because the second wheel touches the cylinder while the first 

 passes over the paper between the upper holes. 



