RECENT ADVANCES IN TELEGRAPHY. 



7.1 



on each side of W, it will not move that wheel, but it will move the 

 wheel X by destroying the balance which previously existed there. 

 But, if a similar extra volume be at the same time sent from B, the 

 pressure in that part of the circuit between IF and X will overcome 

 the opposing forces at each of the points, and both wheels will be 

 worked, each virtually by the distant reservoir and not by its own. 



If we substitute galvanic batteries for the reservoirs, wires for the 

 water-courses, and electricity for the water, this gives us the princi- 

 ple of the duplex telegraph, and it is obvious that no currents passing 

 one another in contrary directions are necessary to it. It will be well to 

 keep this in mind when we come to describe the quadruplex system. 



Following the duplex, the American Automatic system may be 

 said to have been perfected in 1873. The great rapidity with which 

 messages are transmitted and recorded by it is its principal advan- 

 tage, but it has others as requiring a smaller force of operators and 

 less specially skilled. The usual work of a Morse operator is acknowl- 

 edged to be about 1,500 words an hour, and European operators do 

 not average half as much ; but, by the automatic method, to receive 

 and print double that number of words per minute is an ordinary feat, 

 and as many as 7,000 words fourteen pages of this magazine have 

 been legibly recorded in that time. As every word contains, on an 

 average, five letters, and as each letter is represented by a varying 



Earth 



Local Battery 



Fio. 2. Morse Key a^d Eeoister. (Prom Deschanel.) 



number of dots and dashes, each formed by a separate discharge, the 

 circuit, it is calculated, must be "closed" and "broken," and the chem- 

 icals in the battery must cease and recommence their action 60,000 

 times per minute, in the ordinary working of the automatic system. 



