SCIENCE IN THE INDUSTRIAL WORLD 



portant difference, that by means of the radiophone 

 the sound of his voice may be hurled miles instead of 

 feet. 



The sending instrument first used by Doctor De 

 Forest, and which may be taken as the model for suc- 

 ceeding instruments, consists of an ordinary micro- 

 phone transmitter, in which the various vibrations 

 caused by the voice affect the intensity of an electric 

 current. The ether is made to receive a continuous 

 chain of impulses caused by a rapidly vibrating arc 

 light DudelPs arc, as it is called. The oscillations of 

 this arc light are modified in accordance with the varia- 

 tions of the voice as it causes fluctuations of the micro- 

 phone current. These impulses affect the circuit of the 

 receiving apparatus, modify it, and the current so 

 modified passes through the filament of an incandescent 

 lamp, causing the light to vary in accordance with the 

 original vibrations. The variation of the light causes 

 constant changes in the conducting power of the air 

 remaining in the bulb. This rarefied gap in the lamp 

 is used in place of a wire for completing the circuit of a 

 telephone receiver, the varying current causing the re- 

 ceiver to emit sound waves just as the wire telephone 

 does. 



In some of the more recent instruments there is an 

 oscillating arrangement by means of which electrical 

 impulses are constantly sent out at a tremendous rate 

 of repetition. This causes a faint humming in the re- 

 ceivers, altogether too slight to be annoying to the lis- 

 tener. The vibrations of the voice cause lapses or breaks 

 in the oscillating impulses, this arrangement increasing 



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