TELEGRAPHY OF PHOTOGRAPHS BAKER. 



271 



intercept a plan or written message were to have an exactly similar 

 instrument, with the same dimensions, screw threads, and so on, by 

 merely altering the rate of running by 5 or 10 per cent, according to 

 prearranged signals, the picture as received by the intercepting 

 party would be quite unintelligible and confused. 



We have already seen that in the telegraphy of a picture by any 

 system, accurate synchronizing of the sending and receiving appa- 

 ratus is essential. Where a metallic circuit links the transmitting 

 and receiving instruments together, the matter is an easy one, and 

 we have seen in what way it is effected. But when dealing with 

 Avireless work, the question of synchronism becomes more serious. 

 I have employed two methods, each of which appears to answer 



CHRO/VOMCTRIC SY/VCHROf/lSCR FOR WIRE. LESS APPARATUS. 



Fig. 8. 



satisfactorily, and as they are very important I will devote a few 

 moments to their description. 



The first method secures accurate synchronism independently of 

 any Avireless communication. You have already seen how, in the 

 ordinary telegraphic work, the receiving cylinder is driven rather 

 faster than the sending one, and when it finishes up a complete turn 

 too soon it is arrested until the sending cylinder has caught it up, 

 when the latter sends a reverse current, which is responsible for its 

 release. But in the wireless apparatus both sending and receiving 

 cylinders are driven too fast, so to speak — that is, they are made to 

 revolve in four and three-fourths seconds instead of a nominal five. 

 A check comes into play at the end of the revolution, and the cylinder 

 is stopped until the five seconds are completed, the motor working 



