PHOTOTELEGEAPHY AEMAGNAT. 207 



the image; consequently the electro-magnet B receives a current 

 which is a function of this opacity. There is next interposed a de- 

 vice, destined apparently to accelerate the transmission, but whose 

 role seems somewhat problematical. 



Upon the drum C is wound in a helix a steel wire. Every point 

 of this wire passes consecutively under the electro-magnet B, which 

 produces a magnetism proportional to the intensity of the current. 

 This forms the telegraphone of Poulsen. If now O is caused to turn 

 before another magnet connected with the line, in the line there are 

 jDroduced currents which work a string-galvanometer T, which con- 

 trols the light striking the sensitive photographic receiving plate. 



"Wliat is the future of phototelegraphy? At present it would be 

 imprudent to make any prediction. Will a demand be felt for it? 

 Yes, to some extent, especially by the newspapers, which feel a greater 

 and greater need for the rapid transmission of information, often- 

 times in the form of photographs or sketches; by the police for the 

 transmission of the description of criminals, etc. But for all these 

 uses evidently the devices must receive many improvements. 



On the other hand, is it necessary to wait for the demand before 

 making or improving such apparatus? Evidently it is not, for in 

 that case it would be the organ creating the function. Besides we 

 should recall that these experiments are steps toward seeing at a dis- 

 tance, a problem which does not seem susceptible of direct solution 

 and which, proposed more than thirty years ago, has so far led only 

 to phototelegraphy. The latter may well, however, in its turn, lead 

 us to a solution of the original problem. 



