306 TRANSATLANTIC TELEPHONING. 



the dots and dashes begin to run together, and finally form a continuous 

 line. Tried on Dr. Pupin's artificial line without the coils, a few miles 

 was sufficient to render the record illegible. But on introducing the 

 coils, the dots and dashes became at once sharp and distinct, and several 

 messages could be transmitted at the same time over the same line, by 

 using different frequencies, and instruments each tuned to respond to 

 one of these frequencies. What an enormous advantage this would be 

 on an Atlantic cable! The maximum rate of transmission ever reached 

 on an Atlantic cable, and that only as a test, was 40 words per minute. 

 This multiplex transmission would carry this up to 1,500 words, or 

 many times more than is now possible with all the cables working to 

 their full capacity. 



Such is the invention which scientific study and mathematical analysis 

 has made possible. Most electrical engineers would have said that coils 

 of wire, of all things, should be kept out of a telephone line. They 

 are used in alternating current circuits to hold back the current. They 

 are called "choke coils. " They are often used to regulate the current 

 flow. But every electrical engineer knows that while the coil does 

 hold back the current, it does not, like a mere resistance, consume 

 power. Such current as goes through it. goes with little loss of 

 energy, and now that it lias been pointed out, it is easy to understand 

 that while a coil does hold back the current, it does not interfere with 

 the transmission of energy over the line, but, by diminishing the cur- 

 rent, diminishes in a greater ratio the loss on the line, and, above all, 

 serves to preserve the characteristics of the electric waves and so 

 delivers the energy to the receiver in the same form as when it came to 

 the line. 



