ELECTRODE EFFECTS 563 



The complete series of measurements made on the samples dis- 

 cussed above was as follows : 



1. Grounded capacitance of L + N to M-fO. This includes the 

 stray capacitance of the upper electrode to ground and also 

 any fringing effect in the air around the edges of the sample. 



2. Direct capacitance of L + N to M+0. This eliminates the 

 stray capacitance to ground but includes the above fringing, 

 therefore, 2 minus 1 gives the stray capacitance of the 6" 

 square electrode to ground. 



3. Direct capacitance of L + N to ground using M+0 as a shield. 

 This should check 2 minus 1 above. 



4. Direct capacitance from L to M using N as a guard ring and 

 eliminating all fringing and ground capacitance. 



5. Direct capacitance from L to M+0 with N removed. This 

 includes the fringe effect from a small to a large electrode but 

 eliminates the capacitance of L to ground. Hence, 5 minus 4 

 gives the fringe effect. 



6. Grounded capacitance of L to M+0 with N removed. This 

 includes both fringe effect and capacitance of L to ground. 

 Hence, 6 minus 5 gives the capacitance of L to ground. 



7. Same as 6 with 43^" metal ring on top of foil L. 7 minus 6 

 gives the added capacitance due to the ring. 



8. Direct capacitance of L to ground using M+0 as shield. This 

 should check 6 minus 5 above. 



9. Direct capacitance of L to M with N and O removed. This 

 includes the fringe effect between equal electrodes but elimi- 

 nates the capacitance of L to ground. 



10. Grounded capacitance of L to M with N and O removed. 

 This includes the fringe effect and ground capacitance for equal 

 electrodes. 10 minus 9 equals capacitance of L to ground with 

 equal electrodes. 



11. Direct capacitance of L to ground using M as shield. This 

 should check 10 minus 9 above. 



The results of these measurements on a number of samples in- 

 cluding several thicknesses of phenol fibre, hard rubber and glass are 

 given in Table I. In all cases, the capacitance of the leads was 

 measured separately and deducted. The differences between readings 

 as indicated above, and the corresponding check readings are tabu- 

 lated in Table H. 



In using the results tabulated in Table II the directly measured 

 values of stray capacitance to ground (items 2, 6, 12) should be 



