ELECTRICAL CAPACITY OF PLANE PLATES 
219 
It is seen that in the case of rectangular plates equation (3) 
reduces to equation (1). 
The neglect of edge corrections in equations (1) and (3) is 
justified on the same grounds as the similar neglect in the well- 
known formula for parallel plates, C=S/4 ^ d. 
In equations (1) and (3) © may be expressed in terms of r and 
d, figure 34, where d the chord is taken equal to the arc. Arbi- 
trary selection of r will then fix the points on the plates between 
which d is measured. Take r=(r 1 +r 2 )/2 in equations (1) and 
(3) to express the mean distance between the non-parallel plates 
in the two cases. Suppose the equation for parallel plates to be 
applied to non-parallel plates. Equation (3) is applicable in 
the experiment, while the formula for the former case was used. 
Equating the capacities for the two cases, we obtain 
d e = k • d, (4) 
where d is the computed distance for parallel plates of a given 
capacity, d e is the correct mean value for the actual non-parallel 
plates having the same capacity, and k the correction factor. 
Thus, 
k=(r 1 +r 2 )/(r 8 -r 1 ) (Wi+Wg) • 
[(w 2 r 2 -w 1 r 1 )/(r 2 -r 1 ) * logCrg-rjHwg-Wi)] (5) 
In the experiment the value of k was not far from unity. 
