8o PHOTO-TELEGRAPHY 



are the similar parts of the other instrument. One 

 wire of the telephone line is used in each case for 

 the return, the current flowing through the earth. 

 This method has not so far been practically tested, 

 but will doubtless be useful when a greater number 

 of photographs are transmitted. 



The question of the greatest possible length of 

 transmission by the telautograph is daily becoming 

 more important. In 1 908 an experiment was made 

 with Korn's selenium machines between Berlin and 

 London, the two lines Berlin -Paris and Paris - 

 London being joined at Paris by M. Chatenet, who 

 acted as " intermediary." This was necessary 

 owing to the impossibility of speaking clearly from 

 Berlin to London ; anything spoken had therefore 

 to be said to the Paris operator, who " passed it on " 

 to the Berlin operator, and vice versa. Then, 

 when the adjustments were made, the Paris 

 operator simply connected up the Berlin -Paris and 

 Paris -London lines on his switchboard. 



These experiments were, as already stated, 

 carried out with the selenium apparatus, and the 

 current received at London, about 0*25 milliampere, 

 was insufficient to work with. The stronger cur- 

 rent for the synchronising was sufficient to work 

 the relay, however, and as it is of the same mag- 

 nitude as the galvanometer current used in the 

 telautograph there is little doubt but that the latter 

 instrument could be worked effectually between 



