ELECTRODE EFFECTS 



571 



upper electrode plus one-half of the width of the ring. If this equiva- 

 lent ring is of constant width for various sizes of electrodes, the edge 

 correction would be proportional to the radius of the electrode plus 

 a constant. As Fig. 5 shows that the correction in micro-microfarads 

 does not vary greatly with the thickness of the sample, the width of 



% 



i: 



5. 



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Fig. 5— Edge correction versus dielectric constant for samples 6 inches square with 



foil electrodes 



the above hypothetical ring must be approximately proportional 

 to the thickness of the sample. Computations for several samples 

 show that the width of this ring is of the order of twice the thickness 

 of the sample. Hence it appears that as a first approximation the 

 edge correction for various sizes of electrodes may be taken as pro- 



