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BELL SYSTEM TECHNICAL JOURNAL 



duction takes place and that secondary conduction, in which the noise 

 mechanism lies, can take place between the surfaces which are not in 

 primary contact and are not separated by more than a certain increment 

 dx. Figure 14 is an attempt to picture a portion of the hypothetical 

 plane of contact between two carbon granules. 



Fig. 14 — A portion of the hypothetical plane of contact between two carbon 

 granules. The cross hatched circular areas are the coincidence areas through which 

 primary conduction takes place. The shaded areas, through which the secondary 

 electrical conduction takes place, are regions where the granule surfaces are not 

 separated by an interval larger than A.v. The area of each of these is independent of 

 the coincidence area it surrounds. 



The total number of hills in coincidence in a contact is given by 



Nc = i Nx dx = Const. I x" dx = Const. D"+\ 

 Jq Jq 



