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OUR PHYSICAL WORLD 



ence in rates of vibration between the incoming wave and the 

 locally generated wave thus adjusted to any audible frequency so 

 that the signal may be easily heard in the telephone receiver. 

 The result produced is a succession of clear, whistling notes of 

 long and short duration, corresponding to dots and dashes. 



FIG. 126. The heterodyne. Diagram showing the use of the vacuum tube 

 as a generator of continuous waves: (p) plate in tube; (g) grid in tube; (/) fila- 

 ment in tube; (cf) the fixed condenser; (l a ) grid inductance; (/ 3 ) plate inductance; 

 (vc) variable condenser. 



The method employed to cause the vacuum valve to act as 

 a generator of continuous waves may be understood by refer- 

 ence to Figure 126. The inductive coupling between the plate 

 circuit and the grid circuit is shown at m. The inductive coils, 

 between which this coupling is made, are shown at 1 2 and / 3 , 

 and are commonly known as the grid inductance and the plate 

 inductance respectively. 



