12 PHOTO-TELEGRAPHY 



time of transmission. A cartoon was in one 

 instance drawn by Mr. W. K. Haselden in Man- 

 chester and sent by him to the London office of 

 the Daily Mirror, but it was not so satisfactory as 

 the same sketch would have been had it been 

 photographed and then telegraphed to London ; 

 the pencil of the transmitter requires some prac- 

 tice to use it with comfort. 



A method more recently worked out for the 

 transmission of photographs is that of Charbonelle, 

 a French postal engineer, in which once again the 

 Caselli transmitter is employed, and a series of short 

 currents are transmitted which correspond to the 

 interruptions caused by the insulating lines of a 

 sketch or single -line screen half-tone photograph. 

 He has also endeavoured to transmit by a method 

 that has been put to the test by almost every 

 engineer who has paid any attention to the problem 

 of photo -telegraphy, namely, by causing the deposit 

 of silver (or other substance) in the image of a 

 photographic film to act as the means of varying 

 the current transmitted'. This was very carefully 

 investigated by the author in 1907, about a year 

 before the publication of Charbonelle's patent, but 

 although results of a kind were obtained, the idea 

 was abandoned owing to certain fundamental diffi- 

 culties which will probably never be overcome. 



In Fig. 2 is seen a diagrammatic representation 

 of a transverse section of the film of an ordinary 



