RECENT ADVANCES IN TELEGRAPHY. 



75 



The germ of the automatic system, as we have described it, was 

 contained in the " Chemical Telegraph " invented by Alexander Bain, 

 a Scotchman, in 1846. Bain was the first to use the perforated paper 

 to 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 which the steam-engine as 

 known to the ancients does to that of James Watt. Bain's system, 

 improved by the late Sir Charles Wheatstone and known as Wheat- 

 stone'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. It is therefore proper to regard the American Au- 

 tomatic Telegraph as a distinct American invention. In its present 

 form, we owe it to Mr. Thomas A. Edison, of Newark, New Jersey. 



The accompanying cut (Fig. 4) illustrates the results of attempting 





OQpoo 



8 



o 



Fig. 4. 



high speed on the Bain 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 

 electricity 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 re- 

 tards and weakens its action, so that, if suffered to record itself, it 

 would do so by a mark Uke this : - the long after-part 



being caused partly by the accumulated electricity and partly by the 

 second extra current which is in the same direction with the primary 

 one. 



d n ft 



Fig. 5. 



By Mr. Edison's plan the evil is made to cure itself. He simply 

 interposes another wire with a coil, shown at A C JEJ, (Fig. 5). 

 This divides the current, one part of which is again subdivided on 



