On the influence of uniform singularity distributions
  Exact expressions for three-dimensional potential and force yield due to uniform singularity distributed on a finite at rectangular surface have been presented. The expressions, valid throughout the physical domain, have been found to be consistent with other expressions available as special cases of the same problem. Very accurate estimates of the capacitance of a unit square plate and a unit cube have been made using them. 
S. Mukhopadhyay, N. Majumdar