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METHO'DS OF COMMUNICATION FOR FOREST PROTECTION 



transmitter two carbon disks are employed! between which is a quantity of carbon 

 granules. To one of these disks a light metal diaphragm is attached. This diaphragm 

 is caused to vibrate by the sound waves impinging upon it, thereby varying the pressure 



Pig. 73 Solid-back transmitter and transmitter arm 



Fig. 74 Details of the solid-back transmitter 



Line 



Trans. 



r// 



Fig. 75 Diagram of telephone circuit, second stage 



on the carbon granules between the two carbon disks. The transmitter is so wired that 

 these disks and the granules between them are in the battery circuit. The vary ing- 

 pressure, therefore, causes variations in the current which in passing through a receiver 

 reproduces the sounds of the voice. 



