406  Mr.  D.  Owen  on  the  Comparison  of  Electric 
effect  of  the  needle  is  inappreciable,  and  the  product  ^SXcl 
remains  constant.     This  may  be  seen  further  by  the  aid  of  a 
H2-.  2. 
i 
1       \                  ! 
Frequency               \ 
X  cList  apart             j    \ 
or"  platen.                        \ 
(frxd)                         \ 
i 
!      !      ! 
1 
1          i 
i          1 
J}y^lcmc&  apart  ofplales  i?L  cjuj. 
diagram  (fig.  3)  representing  the  lines  of  force  and  the  equi- 
potentials  near  the  needle  when  the  axis  of  the  latter  is 
along  the  direction  of  the  undisturbed  field. 
