1910] on the Telegraphy of Photographs^ Wireless and ly Wire. 855 



shifted off tlie slit, and light will be free to pass through it. Oscilla- 

 tions corresponding to the lines in a photograph or sketch could 

 therefore be utilised to cause shifting of the shutter in the manner I 

 have already described for Korn's telautograph, and a sensitive photo- 

 graphic film could be revolved on a drum behind the slit to receive 

 the picture. Such an apparatus is now in course of preparation, but 

 the amount of light that passes through the slit is extremely small, 

 owing to the fineness of the fibre. Mr. Sanger-Shepherd has there- 

 fore attached a minute shutter to the fibre, crossing the optic axis ; 

 this enables me to use a very much wider slit, and also to adopt the 

 alternative procedure for reception, which you will now see represented 

 in the diagram on the screen. 



For photographic reception the oscillation is passed into the 

 valve detector, and thence to the quartz fibre A B, which is stretched 

 across the field of the magnets (not shown), whose poles are bored 

 with a tunnel through which the beam of light is directed. When 

 the fibre is displaced light is enabled to pass through a fine slit W, 

 and so act on the photographic film. Where, however, the shutter 

 is attached to the fibre a much wider slit can be used, and then a 

 pair of narrow compensated selenium cells S S are placed behind the 

 slit W, a positive ]ens being interposed. When a signal corresponding 

 to a dot in the photograph (i.e. the traversal of a line by the stylus) 

 is received, the fibre shifts, light falls on the cells S S, and their 

 resistance is decreased sufficiently to enable the battery E to actuate 

 the relay R. This closes a local circuit, in which the telectrograph 

 receiver is included, and a mark appears on the paper. In this way 

 a visible record is obtained, which greatly facilitates the process. 



Wireless photo -telegraphy may eventually prove of more utility 

 than the closed-circuit methods, because it would bring America 

 within reach of this country, and would enable communication to be 

 made where telephone or telegraph lines did not exist. It is not 

 limited to photographs — banking signatures, sketches, maps, plans 

 and writing could be transmitted. But I would point out most 

 particularly that the work is as yet in the very earliest stages, and 

 that in giving you some account of it to-night I may be bringing 

 before your notice methods and systems on which a few years hence 

 you will look back with a smile — as curious merely from a historical 

 point of view. 



[T. T. B.] 



