TELEGRAPHIC APPARATUS. 
2 59 
evanescent and momentary; whilst the recorder signals are 
permanently registered, and may be deciphered at leisure. The 
balance with the mirror requires a more complicated artificial 
line than with the recorder. 
Yet it has been found necessary to use the mirror on the 
United States Direct cable between Ireland and Nova Scotia. 
This is the longest cable that has yet been duplexed (2,423 
condensatcur 
de 
transmission 
Fig. 183. 
nautical miles), and it was the first Atlantic cable to which 
the duplex system was applied. The speed of transmission is 
100 letters per minute from each side, or in all about forty- 
five words per minute. Experience has shown that the duplex 
system practically doubles the capacity and commercial value 
of the cable ; and the Eastern Telegraph Go ., by the energy of 
its general manager, Sir James Anderson, found out as early as 
1876 the advantages of a system that, by increasing so much 
the number of words transmitted in a given time, augmented 
in the most satisfactory manner the earning powers. 
s 2 
