1910] 071 the Telegraphy of Photographs, Wireless and ly Wire. 849 



The wireless apparatus for transmitting sketches, writing, or simple 

 photographic images over distances up to about fifty miles may 

 perhaps be looked upon as rather rudimentary, but I shall be able 

 to show from actual results that it is at any rate practicable, and it 

 is certainly more simple than any method based on later wireless 

 researches. 



I will first show you an experiment, for the simplicity of which 

 I must ask your pardon ; but it illustrates so clearly how easy it 

 really is to transmit a photograph by wireless under ideal conditions. 

 I have here a small electric lamp, coupled up with the local side of 

 a relay and battery, the relay being actuated by means of a coherer 

 detector. At the other side of the platform there is a Morse key, 

 which, when depressed, closes the primary circuit of an induction 

 coil, the secondary being coupled up in the usual way to give oscilla- 

 tions. When I press the key, and thereby send a signal, you see 

 that the lamp at once lights up. If the coherer be tapped the lamp 

 is extinguished, and another tap of the Morse key causes it to Hght 

 again. 



Now suppose that the taps of the Morse key were controlled by 

 the lines in a photograph or sketch, and that the light from the 

 lamp were concentrated on a revolving photographic film, and you 

 will see at once how a photograph could be transmitted by wireless 

 telegraphy. 



Such a process would be utterly impracticable commercially, but 

 my telectrographic system can be used with success in its place. A 

 line picture prepared in the way already described is attached to the 

 drum of the transmitter, and the intermittent current which is 

 ordinarily passed into the telephone line goes into an electromagnet, 

 M in Fig. 4, which then attracts a soft iron diaphragm attached to 

 brass springs, which are fixed to two rigid supports. Every time 

 current flows through the magnet coils this diaphragm is attracted 

 to it, and the platinum contacts P Q are brought together ; when 

 the current flows, and P Q are in contact, the primary circuit of a 

 transformer is closed, and the secondary having a spark gap and 

 being inductively coupled to the aerial and earth, a signal is trans- 

 mitted into space. Thus in the wireless transmitter the only 

 difference from ordinary telegraphy lies in the fact that the length 

 of the signals and theii* distance apart is regulated by the Hues 

 composing the sketch or photograph. 



When working with high voltages in the primary, such as 110, 

 arcing is liable to take place, and hence the distance between p and q 

 when not attracted must be considerable. This means that the 

 distance between the diaphragm clamps, s s in the figure, must be 

 short, and the German-silver spring of which the diaphragm is made 

 must be thick, these two conditions making the natural period of 

 vibration very short. I have, however, found that by interposing 

 a mercury motor-interrupter in the primary circuit, arcing is 



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