.irri.ic.irio.w or sr.irisric.u. methods 



47 



wide variation in tlu- ohsorxations, and to llu' fact thai tin- frc(|iK"nc" 

 histogram apfx-ars to be biniodal.' Methods of dcahni^' with such 

 distributions will he considered. 



Samples of carbon having different molecular surface .'•tructures 

 have ditTerent resistances. To put it in a still more practical way, 

 if the nuinufacluring process is not controlled within very narrow 

 limits, wide variations are produced in the molecular properties o\ 

 the carbon. The microphonic properties of these carbons are there- 

 fore ditTerent. One of the problems with which we have been con- 

 cerned is to determine the relationship existing between the physical 

 and chemical characteristics of the carbon and the resistance of the 

 material when measured under clifTerent conditions. We are obvi- 

 ously ilealing in this case with problems invoking the measurement 

 of physical (luantities which cannot be controlle<l e\en in the laliora- 



Fig. 2 



'If curves which touch the axis at + » and — » have more than one value 

 of the variable lor which the derivative of the frequency in respect to the 

 variable is equal to zero — the points being other than that for which the fre- 

 quency is zero — these curves are referred to as bimodal, trimodal, etc. The 

 modal value is the most probable one and is of particular interest in uni- 

 modal curves. 



