COFFIN. 



EDGE CORRECTIONS IN CONDENSERS. 



429 



Looking at the plot, we notice the remarkable rapidity with which the 

 projecting edge acts as if it were an infinite plane. In fact, for all pur- 

 poses a projection of ten or twenty times the distance apart acts as 

 nearly as possible as an infinite plane, as far as the electricity on the 

 inside face is concerned. 



J. J. Thomson has found for the amount 

 of electricity on the side P Q the expres- 

 sion : 



(Ipq 



log 



2h 



CO- 



OO- 



By the method of electrical images it is 

 easily seen that for the case I, the expres- 

 sion is : 



00 . 



I 

 h 



I 



OD 



Ih 



11 



CO 



^-x^y 



CO 



This problem was also completely solved with the following coordinates 

 for the corners, where a S 1. The solution for the quantity of elec- 

 tricity on the smaller plate being 



CO 



t — CO 



— V ( h 



47rA [ 



+ 



ri — a 





+ 1 — log 



a + 



1i "^^ 



00 



This reduces to the correct expression for the 

 case a = 1 ; but to obtain that for a rectangu- 

 lar corner near an infinite plane it cannot be ap- 

 plied, hence the change to the above notation. 



t ~ a 



