PHOTOTELEGRAPHY.* 



By Henri Armagnat, 

 Consulting engineer, expert for the Tribunal Civil de la Seine. 



The transmission of pictures to a distance by the electrical current 

 is not a new idea. It had its inception perhaps some thirty years 

 ago when electricity itself was developing, and even then furnished 

 ground for hopes which are to-day partially realized. The inven- 

 tion of the photophone by Graham Bell had made generally known 

 the sensitiveness to light of selenium, and its utilization for the trans- 

 mission of pictures was at once proposed by many. These attempts 

 were unsuccessful. Indeed, during the last thirty years no further 

 advance has been made in the direct reproduction at a distance of the 

 images of real animate objects. 



But if we restrict our problem to requiring electricity to send and 

 reproduce, point by point, an inanimate picture, we shall find several 

 interesting solutions, some of which have had practical trials and 

 require but little further development to be commercially practicable 

 whenever a demand for phototelegraphy grows. 



The transmission of pictures containing only blacks and whites 

 without any half-tones was tried in 1851 by Backwell, in 1855 by 

 Caselli, and finally by d'Arlincourt in 1872. All these inventors had 

 in view not the sending of a picture, but the transmission of writing. 

 Their purpose was to send autographs by means of the telegraph, 

 but they naturally could have reproduced equall}?^ well other pen 

 designs. As the phototelegraphy of to-day still embodies these early 

 ideas, it is really no innovation. 



In order to reproduce in B an image, A (fig. 1), it suffices to move 

 over A a style, «, so that it follows successively a series of verj^ close 

 parallel lines, while by some suitable means a second style, h, follows 

 upon the receiver, B, traces similar to those upon A, occupying at 

 each instant a position upon B similar to that which a has upon A. 



"Translated, by permission, from the Revue Scientifique, April 18, 1908; 

 fifth series, Vol. IX, No. 16, Paris, 1908. 



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