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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



rent for reproducing at the receiving station the image at tlie sending 

 station. 



We will not describe here the device used by Korn for making 

 manifest this image. He used the cathode rays produced by currents of 

 high frequency and a very sensitive galvanometer. This very ingen- 

 ious receiving device was, however, too delicate for ordinar}?^ practice 

 and is to-day replaced by a much simpler and rougher apparatus. 



The current sent by the transmitter passes through a string- 

 galvanometer, which is made to more or less obscure a window, «?, 

 through which a luminous pencil of rays, emanating from the lamp, 

 A;, and concentrated by the lens, /, enters the dark chamber which 

 holds the receiving cylinder, j. The latter turns upon its axis simi- 

 larly to the transmitting cylinder and is covered with a sensitive 

 photographic film. The lamp, h, and the lens, Z, are so placed as to 

 produce upon this film a ver}^ minute point of light ; the varying 

 I diaphragm carried by the string- 



V galvanometer renders the intensit}^ 



— ^ of this point of light proportional, 



or inversely proportional, to the 

 current coming over the line, and 

 consequently to the opacitj^ or 

 transparency of the corresponding 

 ])oint of the image we vrish to 

 reproduce. The impression upon 

 the film varies with regard to the 

 original image according to the 

 mode of disposition of the dia- 

 phragm so that it is possible to 

 obtain a positive or negative reproduction. It remains onl}^ to de- 

 velop the film to have the complete reproduction of the image sent 

 over the line. 



Figure 2 indicates the device used for the synchronism : The lever, 

 w, passes very close to the disk, ^', and stops that disk when n hits the 

 spur, ,io; as the movement from the electric motor is transmitted to 

 the cylinder through a friction clutch formed by the cone, h, and the 

 box, i, the motor continues to turn ; as soon as the transmitting vy\- 

 inder, «, comes to the proper point, the finger, /, will touch the spring, 

 (7, breaking the current which traverses the olectro-n)agnet, t; the 

 latter frees its armature, the lever, ?/, comes away from /, freeing the 

 cylinder which then resumes its rotation. The same course of events 

 recurs at each turn of the cylinder, correcting the small variations in 

 its speed, provided only that the receiving cylinder, j, turns a little 

 faster than the transmitter, a. 



Let us examine some further details of the apparatus. The seleni- 

 um cell is formed of a little slab of stone or slate, figure 3, upon which 



Fig. 3. — Selenium cell. 



