TELEGRAPHY. 



723 



word contains, on an average, five letters, and 

 as each letter is represented by a varying num- 

 ber of dots and dashes, each formed by a sepa- 

 rate discharge, the circuit, it is calculated, must 

 be " closed" and " broken" and the chemicals 

 in the battery must cease and recommence 

 their action 60,000 times per minute, in the 

 ordinary working of the automatic system. 



In every form of electric telegraph the sig- 

 nals are given by an intermittent flow of elec- 

 tricity. In the Morse system a " key," Fig. 3, 

 is used which, in its normal position, "breaks" 

 the circuit, but when depressed by the finger 

 of the operator allows the electricity to pass 

 through it on its mission. Arrived at the dis- 

 tant 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 different. 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 systems 

 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 oper- 

 ator with his key, and, the time occupied in 

 transmitting being so vastly less, the " auto- 

 matic " may claim to have rendered old-fash- 

 ioned telegraphy 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 arrangement does duty as a reg- 

 ister. 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 de- 

 composes the moisture of the paper into oxy- 

 gen and hydrogen, and oxidizes or rusts the 

 pen. A little of this oxide is rubbed off by the 

 quickly-moving paper, and enters into combi- 

 nation with the chemical still contained in it, 

 producing a stain in the form of a dot or dash 

 which corresponds with the holes punched in 

 the paper at the sending-station (Fig. 4). 

 Where three holes come together, both wheels 

 form a contact, and a dash is produced, because 

 the second wheel touches the cylinder while 



the first passes over the paper between the up- 

 per holes. 



The germ of the automatic system was con- 

 tained in the " Chemical Telegraph " invented 

 by Alexander Bain, a Scotchman, in 1846. Bain 

 was the first to use the perforated paper to 



FIG. 4. 



transmit and the chemically-prepared paper to 

 receive the message. But his invention, from 

 a practical point of view, bears about the same 

 relation to the American system that the 

 steam-engine, as known to the ancients, does 

 to that of James Watt. Bain's system im- 

 proved by the late Sir Charles Wheatstone and 

 known as Wheatstone's automatic system, is 

 employed to a limited extent in Great Britain ; 

 but, thus improved, its speed does not exceed 

 60 to 100 words a minute. 



The accompanying cut (Fig. 5) illustrates the 

 results of attempting high speed on the Bain 



00 O 



t 





FIG. 5. 



telegraph. Instead of recording themselves by 

 decided dots and dashes, the electric discharges 

 leave indistinct and elongated traces, which, 

 when the speed amounts to 300 words or over, 

 run into one another and make a continuous 

 line. This effect is due to the property which 

 all electrified bodies have of inducing electrici- 

 ty in neighboring bodies. The earth, reacting 

 on the line wire suspended above it, induces in 

 it what is called an extra current, both on 

 closing and breaking the circuit. On first 

 closing the circuit the extra current runs in the 

 contrary direction to the primary, and retards 

 and weakens its action, so that, if suffered to 

 record itself, it would do so by a mark like this : 

 mump the long after-part being 



caused partly by the accumulated electricity, 

 and partly by the second extra current which 



FIG. 6. 



is in the same direction with the primary one. 



In the American system this evil is made to 



cure itself. The inventor simply interposes 



