202 



ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1908. 



The plan of the apparatus (fig. 5) will show how this compensation 

 takes place. Two selenium cells, Se^ and Se,, form two branches of a 

 Wlieatstone's bridge, the resistances, A and B, serving for the other 



two arms. A battery furnishes 

 the current through two op- 

 posite junctions of the bridge, 

 the line and the galvanometer 

 being connected to the two re- 

 maining junctions. The cell, 

 Se^, is placed in the sending 

 apparatus; it is exposed di- 

 rectly to the light transvers- 

 ing the picture which is to be 

 transmitted ; the cell, Se,, is 

 lighted by an auxiliary source, 

 obscured by the galvanometer, 

 ^, and the apparatus is so 

 devised that as Se^ receives 

 light, the equilibrium of the 

 bridge is broken ; but the gal- 

 vanometer, </, in deviating 

 uncovers more or less the 

 auxiliary beam so that Se, 

 becomes illuminated and tends 

 to reestablish the equilibrium. 

 The galvanometer of com- 

 pensation and the receiver, 

 G, receive the same current. 

 The difference between figures 

 2 and 5 is that, in the working 

 apparatus, the cell and the 

 compensating galvanometer 

 are both at the transmitting 

 station. 



The Korn system is the only 

 one which has been practically 

 tried with the transmitter sep- 

 arated from the receiver. In 

 the trials between Munich and 

 Berlin, during the year 1907, 

 the transmission of a jDicture loO by 240 millimeters, reduced to ap- 

 proximately 35 by 64 millimeters at the receiving station, was ac- 

 complished in six minutes. These trials were made over a double 

 telephone line and at night in order to avoid the disturbances pro- 

 duced by the neighboring lines. 



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