54 PHOTO-TELEGRAPHY 



current possible to work with, and we frequently 

 only received about half. The optical arrange- 

 ments could, of course, be easily modified to com- 

 pensate for this, but unless the tension in the 

 galvanometer strings was above a certain figure, 

 its action was uncertain. 



Induction from other lines was very marked at 

 certain times, and at first it was thought that this 

 was due to weather conditions. The observed 

 facts, however, showed this not to be the case ; 

 induction effects were chiefly due to line condi- 

 tions. The two systems of telegraphy, Morse and 

 Baudot, gave marked induction effects, and tele- 

 graphic experts declared they could actually read 

 Morse messages on some of the photographs. 

 Induction effects can be seen on looking at the 

 photograph shown in Fig. 26, where they cross 

 the photograph at regular intervals. 



The photographic image, as will have been 

 gathered, consists really of one long spiral line of 

 varying thickness and intensity, which becomes 

 resolved into parallel lines when the image is 

 changed from its cylindrical form and laid out flat. 

 The thickness of the line is increased by the in- 

 duction, hence the dots and dashes are graphically 

 represented in the received photograph. 



In the Baudot telegraphic system there is a 

 periodic current, and the stripes seen are at 

 regular intervals across the picture. These marks 



