572 BELL SYSTEM TECHNICAL JOURNAL 



portional to r-\-t, r being the radius of the electrode and / the thickness 

 of the sample. Table V shows a series of measurements on one 

 sample with electrodes of several different sizes. In this table the 

 edge correction C has been taken as the difference between the capaci- 

 tances measured with and without a guard ring. This includes the 

 direct capacitance of the upper electrode to ground. It will be seen 



that while the value of is not exactly constant it varies much less 



/' + / 



than — . Hence if Ci is the edge correction for an electrode of radius 

 r 



ri the edge correction for an electrode of radius rz under similar con- 

 ditions would be approximately 



This, of course, applies only to the case of one large and one smaller 

 electrode. For the case of the equal electrodes t in the above ex- 

 pression probably should be multiplied by a constant of the order 

 of 0.4. 



